[Federal Register Volume 88, Number 46 (Thursday, March 9, 2023)]
[Proposed Rules]
[Pages 14536-14560]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-04680]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
[Docket No. FWS-R8-ES-2022-0165; FF09E21000 FXES1111090FEDR 234]
Endangered and Threatened Wildlife and Plants; Petition Finding
for Joshua Trees (Yucca brevifolia and Y. jaegeriana)
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Notification of finding.
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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), announce a
12-month finding on a petition to list Joshua trees (Yucca brevifolia
and Y. jaegeriana) as endangered or threatened species under the
Endangered Species Act of 1973, as amended (Act). After a thorough
review of the best available scientific and commercial information, we
find that listing Joshua trees as endangered or threatened species is
not warranted. However, we ask the public to submit to us any new
information that becomes available concerning the threats to the Joshua
trees or their habitat at any time.
DATES: The finding in this document was made on March 9, 2023.
ADDRESSES: This finding is available on the internet at https://www.regulations.gov under Docket No. FWS-R8-ES-2022-0165. Supporting
information that we developed for this finding, including the species
assessment form, species status assessment report, and peer review, are
available at https://www.regulations.gov under Docket No. FWS-R8-ES-
2022-0165 and on the Service's website at https://www.fws.gov/office/carlsbad-fish-and-wildlife/library. Supporting information is also
available for public inspection, by appointment, during normal business
hours at the U.S. Fish and Wildlife Service, Carlsbad Ecological
Services Field Office, 2177 Salk Avenue, Suite 250, Carlsbad, CA 92008.
Please submit any new information, materials, comments, or questions
concerning this finding to the person listed under FOR FURTHER
INFORMATION CONTACT.
FOR FURTHER INFORMATION CONTACT: Scott Sobiech, Field Supervisor, U.S.
Fish and Wildlife Service, Carlsbad Ecological Services Field Office,
2177 Salk Avenue, Suite 250, Carlsbad, CA 92008; telephone 760-431-
9440. Individuals in the United States who are deaf, deafblind, hard of
hearing, or have a speech disability may dial 711 (TTY, TDD, or
TeleBraille) to access telecommunications relay services. Individuals
outside the United States should use the relay services offered within
their country to make international calls to the point-of-contact in
the United States.
SUPPLEMENTARY INFORMATION:
Previous Federal Actions
On September 29, 2015, we received a petition from Taylor Jones
(representing WildEarth Guardians), requesting that Yucca brevifolia--
either as a full species (Y. brevifolia) or as two subspecies (Y. b.
brevifolia and Y. b. jaegeriana)--be listed as threatened and, if
applicable, critical habitat be designated. On September 14, 2016, we
published a 90-day finding in the Federal Register (81 FR 63160)
concluding that the petition presented substantial information
indicating that listing the Joshua tree may be warranted. On August 15,
2019, we published a 12-month finding (84 FR 41694) concluding that
listing either Y. brevifolia or Y. jaegeriana was not warranted. On
November 4, 2019, WildEarth Guardians filed a complaint in the Central
District of California challenging the analyses and listing decisions.
The court vacated and remanded the listing decisions back to the
Service (WildEarth Guardians v. Haaland, 2021 WL 4263831 (C.D. Cal.
September 20, 2021)), ordering us to reconsider whether the two species
of Joshua tree should be listed under the Act.
The Service has reassessed its August 2019 12-month finding and
revised the species status assessment (SSA) report. This document
complies with the September 20, 2021, court-ordered remand of the
August 2019 ``not warranted'' 12-month findings for the two species of
Joshua tree (Yucca brevifolia and Y. jaegeriana) and constitutes our
new 12-month findings on the September 29, 2015, petition to list the
Joshua tree species under the Act.
Supporting Documents
A species status assessment (SSA) team prepared an SSA report for
Joshua trees (Yucca brevifolia and Y. jaegeriana). The SSA team was
composed of Service biologists, in consultation with other species
experts. The SSA report and the information
[[Page 14537]]
reviewed represents compilations of the best scientific and commercial
data available for the species, including the impacts of past, present,
and projected future factors (both negative and beneficial) affecting
the species, that we used to make our determination of status for the
species.
In accordance with our joint policy on peer review published in the
Federal Register on July 1, 1994 (59 FR 34270), and our August 22,
2016, memorandum updating and clarifying the role of peer review of
listing actions under the Act, we sought the expert opinions of nine
appropriate specialists regarding the SSA report for the Joshua trees.
We received responses from five peer reviewers. We also coordinated
with the California Department of Fish and Wildlife, Nevada Department
of Wildlife, Arizona Department of Agriculture's Environmental Services
Division, and the Utah State Department of Natural Resources and
Natural Heritage Program during the development of the SSA report for
the Joshua trees.
Background
Species Information
In this discussion, we present an overview of the biological
information for Joshua trees (Yucca brevifolia and Y. jaegeriana). For
the purposes of this analysis, we discuss both species together using
the common name--Joshua tree(s)--when the discussion of information
pertains to both species. Literature or conclusions specific to a
single species are indicated by the species' scientific name, where
applicable.
Species Description
Joshua trees are long-lived plants that occur in desert regions of
the southwestern United States including portions of California,
Arizona, Nevada, and Utah, well beyond the Joshua Tree National Park in
California. Joshua trees are found throughout the Mojave, Great Basin,
and Sonoran Deserts. Joshua trees have generally been addressed in the
literature as a single species; however, recent references have
identified at least two varieties or subspecies (Yucca brevifolia var.
brevifolia and Y. b. var. jaegeriana). We consider the two entities to
be two distinct species, the western Joshua tree (Yucca brevifolia) and
eastern Joshua tree (Y. jaegeriana) based on expert analysis, and we
treat them as two separate, listable entities. The SSA report has
additional detailed descriptive information on Joshua trees (Y.
brevifolia and Y. jaegeriana) (Service 2023, entire).
Yucca brevifolia--Yucca brevifolia is a 16-40 feet (ft) (5-12
meters (m)) tall, evergreen, tree-like monocot. The leaves are between
7.5 and 14.6 inches (in) (19-37 centimeters (cm)) long and are
clustered in rosettes at the branch ends. Branching only occurs
following flowering events where one or more lateral shoots develop
from the base of the inflorescence (cluster of flowers) (McKelvey 1938,
p. 130; Simpson 1975, p. 32). The flowers on the inflorescence are
nearly spherical with short, wide petals that curve over the tip of the
pistil and occur in dense, heavy panicles. Tegeticula synthetica, a
species of yucca moth, pollinates the flowers; and the resulting seed
pods require mechanical action (e.g., a rodent) to open and for the
seeds to be dispersed. In addition to sexual reproduction, the species
can also reproduce asexually through basal resprouts, particularly when
under stress. Yucca brevifolia is long-lived (100 to several hundred
years old), with a generation time of 50 to 70 years.
Yucca jaegeriana--Yucca jaegeriana is a shorter (9-20 ft; 3-6 m),
evergreen, tree-like monocot. Yucca jaegeriana has shorter leaves (less
than 8.7 in (22 cm)) and shorter height to first branching at 2.3-3.3
ft (0.75-1.0 m) than Y. brevifolia, which results in a denser canopy
(see figure 3-1 in the SSA report; McKelvey 1938, p. 138; Service 2023,
p. 9). The flower is elongate with narrow petals that wrap around the
pistil forming a corolla tube. Tegeticula antithetica, a species of
yucca moth, pollinates the flowers. The variation in floral morphology,
specifically style length, between Y. brevifolia and Y. jaegeriana is
strongly correlated with the physical characteristics of its obligate
moth pollinator due to coevolution with Tegeticula antithetica having a
shorter ovipositor than the Y. brevifolia pollinator, T. synthetica
(see figure 3-1 in the SSA report; Godsoe et al. 2009, p. 820; Yoder et
al. 2013, p. 11; Service 2023, p. 9). The resulting seed pods require
mechanical action (e.g., a rodent) to open and for the seeds to be
dispersed. In addition to sexual reproduction, the species can also
reproduce asexually through basal resprouts, particularly when under
stress. Yucca jaegeriana is long-lived (100 to several hundred years
old), with a generation time of 50 to 70 years.
Hybrids--Hybrids occur in a smaller geographic area compared to the
rest of the range, toward Joshua trees' northern limit, where the
distribution of both species overlap, and are not reliably identifiable
from morphological characteristics alone (Smith 2022, pers. comm.). The
hybrid zone was not included in our assessment of viability for Yucca
brevifolia and Y. jaegeriana, although that zone confers additional
resiliency, redundancy, and representation to both species.
Taxonomy
Yucca brevifolia var. jaegeriana was determined to be a distinct
species based on morphological and pollinator differences (Lenz 2007,
p. 100) and restriction-site-associated DNA (RAD)-sequencing (Royer et
al. 2016, p. 1730). These analyses concluded that Y. b. var. jaegeriana
should be raised to specific rank (Lenz 2007, p. 97) and that it is
genetically distinct from Y. b. var. brevifolia (Royer et al. 2016, p.
1736). Additionally, Y. brevifolia diverged at least 5 million years
ago, possibly due to geographic separation by the Bouse Embayment (a
Pliocene Era chain of lakes) (Smith et al. 2008a, p. 2682). As
described above, the two taxa, and their obligate moth pollinators,
come into contact and plant hybridization occurs in the Tikaboo Valley,
Nevada, (Starr et al. 2013, p. 4; Royer et al. 2016, p. 136).
Based on these analyses (Lenz 2007, entire; Smith et al. 2008b,
entire; Royer et al. 2016, entire), and correspondence between the
Service and editors of the Jepson Manual (Wallace 2017, p. 2), we
consider Yucca brevifolia var. brevifolia and Y. b. var. jaegeriana to
be two distinct species, and we treat them as two separate listable
entities: Y. brevifolia and Y. jaegeriana, respectively. For additional
information on Joshua tree taxonomy, see section 3.2 of the SSA report
(Service 2023, p. 9).
Habitat/Life History
Joshua trees occur in desert regions of the southwestern United
States and are located on alluvial fans, plains, and bajadas throughout
the Mojave, Great Basin, and Sonoran Deserts. Joshua trees occur
throughout a wide range of vegetation communities between approximately
1,279 and 8,775 ft (390 and 2,675 m) elevation. Joshua trees are often
the tallest plants on the landscape where they occur but are not
typically dominant in terms of vegetation cover. Joshua trees are a
slow-growing desert plant. Because they do not have growth rings,
accurately determining the age of Joshua trees is difficult. The height
of a Joshua tree divided by an estimate of growth per year is used to
estimate age. Joshua trees can live for several hundred years, though a
more common lifespan is about 150 years, and have a generation time of
50 to 70 years. They can reproduce via several mechanisms, have unique
habitat and ecological needs, and can disperse through environmental
and biological means.
[[Page 14538]]
Joshua trees' life cycle includes seedling, established individual,
juvenile, and adult stages (see figure 3-2 in the SSA report (Service
2023, p. 11)).
The life history of both Yucca brevifolia and Y. jaegeriana relies
on a complex set of interactions between individual plants, yucca
moths, seed dispersers, herbivores/predators, and abiotic conditions
for successful reproduction and survival to a reproductively mature
adult (see figure 3-2 in the SSA report (Service 2023, p. 11)). Joshua
trees reproduce sexually through pollination and seed production as
well as asexually through vegetative growth (clones). The relative
contribution of sexual and asexual reproduction and whether the
proportion varies regionally is not known. The clonal growth strategy
likely increases persistence of individuals and populations when under
stress. Optimal reproduction and recruitment of Joshua trees requires a
convergence of events, including fertilization by its obligate
pollinators (Pellmyr and Segraves 2003, p. 721), seed dispersal and
caching by rodents (Vander Wall et al. 2006, p. 543; Waitman et al.
2012, p. 5), seedling emergence from a short-lived seed bank triggered
by isolated late-summer rainfall (Reynolds et al. 2012, p. 1652), and
exposure to cold temperatures that improve seedling and juvenile growth
and survival (Went 1957, p. 173). For additional information, see the
SSA report's section 3.4 (Service 2023, p. 10).
Historical and Current Range/Distribution
Historical Distribution--Joshua trees have occurred in southwestern
deserts for at least 6 million years (Smith et al. 2008a, p. 255),
persisting through several geologic time periods characterized by
variable climate conditions (temperature and precipitation patterns).
Joshua trees' historical distributions are based on a 2022 empirical
study conducted throughout the range of Yucca brevifolia and Y.
jaegeriana and we estimate 9,642,136 acres (ac) (3,903,699 hectares
(ha)) were occupied historically (see figure 4-1 in the SSA report;
Esque 2022b, pers. comm.). All areas where adult Joshua trees were
recorded are considered part of the historical range over an
approximate time period of 1900 to 1950, based on the lifespan of
Joshua trees and development trends in the region. Presence, absence,
and status (alive, dead, or ornamental) of adult Joshua trees were
assessed through aerial interpretation and ground truthing of aerial
imagery within quarter square kilometer (500 m by 500 m) grid cells.
This method could not be applied in the northern portion of the
species' range near Nellis Air Force Base in southern Nevada.
Therefore, for the species' range near Nellis Air Force Base, we rely
on the distribution from the 2018 Joshua tree SSA (Service 2018, p.
11), which provides the best available data for Joshua tree
distribution in this area.
Current Distribution--The current range of Joshua trees extends
from northwestern Arizona to southwestern Utah west to southern Nevada
and southeastern California (see figure 4-1 in the SSA report (Service
2023, p. 31)). Joshua trees are currently distributed over several
large discontinuous areas totaling 9,447,883 ac (3,825,054 ha) of a
much larger region. The refined distribution presented in the SSA
report is based on a 2022 USGS empirical study conducted throughout the
range of Yucca brevifolia and Y. jaegeriana (Esque 2022b, pers. comm.;
Service 2023, pp. 30-31). Very little of the historical range has been
lost; the current distribution of Joshua trees is reduced by
approximately 3 percent compared to the historical distribution. The
current distribution is less acreage than we reported in the previous
2019 SSA report (12,144,840 ac; 4,906,749 ha). The previous
distribution was based on the records and reports available at that
time (Service 2019, p. 14). Although our updated current distribution
is less than previously reported, it is not based on a loss of habitat;
rather it is an updated estimate of current distribution of the species
based on new, more accurate, information. Please see sections 4.1 and
4.2 of the SSA report for further information on Joshua trees'
historical and current distributions (Service 2023, pp. 30-31).
BILLING CODE 4333-15-P
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[GRAPHIC] [TIFF OMITTED] TP09MR23.014
BILLING CODE 4333-15-C
Species Ecological Needs
A species' biological condition should be evaluated relative to the
three conservation biology principles of resiliency, redundancy, and
representation (Shaffer and Stein 2000, pp. 306-311). Briefly,
resiliency describes the ability of the species to withstand
environmental and demographic stochasticity; redundancy describes the
ability of the species to withstand catastrophic events; and
representation describes the ability of
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the species to adapt over time to long-term changes in the environment.
In general, the more redundant, representative, and resilient a species
is, the more likely it is to sustain populations over time, even under
changing environmental conditions. Below we describe the population-
and species-level needs for Joshua trees that were used to evaluate
resiliency. These concepts will be discussed in more detail in the
Analytical Framework section below.
Population Needs
Joshua trees require that habitat and demographic needs are met for
population resiliency. Joshua trees rely on habitat elements that
include appropriate substrate, appropriate climatic conditions, yucca
moth pollinators, rodent seed-caches, nurse plants, and dispersal.
Appropriate climatic conditions include adequate amounts of annual
precipitation (4.7-16.9 in (11.8-42.9 cm)), summer monthly
precipitation in excess of 1.1 in (2.9 cm) in the months of July and
August, average summer temperatures based on the range experienced
historically (67 to 91 degrees Fahrenheit ([deg]F); 19.4 to 32.8
degrees Celsius ([deg]C)), and winter temperatures between 29 and 50
[deg]F (-1.7 and 10 [deg]C). To reproduce successfully, Joshua trees
need yucca moth pollinators, nurse plants, and seed-caching rodents.
The demographic needs that Joshua trees require are survival,
abundance, recruitment, and dispersal. Sufficient growth and survival
at all life stages is required for an individual to reach sexual
maturity and to maintain an abundant population. A diverse age
structure is important for withstanding variability in climate and the
pressures of threats such as drought, herbivory, and wildfire because
young age-classes are more susceptible to mortality during these events
than adults.
Joshua trees require populations of sufficient abundance to be
maintained over time with stable or increasing population growth.
Sufficient abundance is achieved through survival of young age classes
to adult, successful reproduction, and recruitment to support the next
generation. There must be adequate survival at all life stages to
support an abundant adult population. We currently lack a population
viability analysis and information on the abundance at each age class
required to maintain resiliency. Sufficient recruitment is necessary to
maintain the population over the long term. In particular, seed set
needs to be high enough to ensure future recruitment considering seed
predation and the low percentage of viable seed that germinate and
survive to reproduce. Dispersal of propagules is important for gene
flow to maintain appropriate levels of genetic variability. Dispersal
also allows for potential recolonization of sites following
disturbance. See chapter 5 of the SSA report for further information on
population needs (Service 2023, pp. 41-50).
The 2023 SSA report analyzes resiliency within six analysis units
including two populations of Yucca brevifolia (YUBR North and YUBR
South), three populations of Y. jaegeriana (YUJA North, YUJA East, and
YUJA Central), and a hybrid zone (described further in section 4.5 of
the SSA report (Service 2023, pp. 36-40)). With the exception of the
hybrid zone, we use these five analysis units to analyze both current
conditions and future conditions in this document and the SSA report
(Figure 1, Table 1).
Table 1--Summary of Analysis Units Used in the SSA Report
[This table appears in the SSA report as table 4-3; Service 2023, p. 37]
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Occupied habitat ac
Population (ha) Elevation range ft (m) Land ownership (%) *
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YUBR North........................... 2,129,113 (861,989).... 2,475-8,775 (754-2675). Federal: 97.6, State:
0.51, Private: 1.6.
YUBR South........................... 2,288,162 (926,381).... 1,922-7,640 (586-2,328) Federal: 52.3, State:
2.1, Private: 45.6.
YUJA North........................... 2,065,476 (836,225).... 1,540-7,961 (469-2,426) Federal: 98, State:
0.9, Private: 1.1.
YUJA Central......................... 2,089,163 (845,815).... 1,626-7,627 (495-2,325) Federal: 91, State:
1.9, Private: 7.9.
YUJA East............................ 754,821 (305,595)...... 1,279-5,067 (390-1,544) Federal: 59.8, State:
16.7, Private: 23.5.
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* Local ownership was less than 1 percent for all analysis units.
Species Needs
Species needs are an exploration of what influences redundancy and
representation for Joshua trees. This requires an examination of the
Joshua trees' evolutionary history and historical distribution to
understand how Joshua trees function across their range. To maintain
redundancy, numerous local Joshua tree populations need to be
distributed widely across the landscape with some degree of
connectivity to withstand catastrophic events. Finally, to maintain
representation, which is needed by the species to respond to changing
environmental conditions, genetic diversity must be maintained by
preserving populations that are morphologically, geographically, or
ecologically diverse. In general, Joshua trees need multiple, large,
sufficiently resilient populations distributed across the range of
ecological variability to have the redundancy and representation to
withstand catastrophic events and adapt to environmental change given
the trees' moderate adaptive capacity. See chapter 5 of the SSA report
for further information on population needs (Service 2023, pp. 41-50).
Regulatory and Analytical Framework
Under section 4(b)(3)(B) of the Act (16 U.S.C. 1531 et seq.), we
are required to make a finding whether or not a petitioned action is
warranted within 12 months after receiving any petition for which we
have determined contains substantial scientific or commercial
information indicating that the petitioned action may be warranted
(``12-month finding''). We must make a finding that the petitioned
action is: (1) Not warranted; (2) warranted; or (3) warranted but
precluded by pending proposals to determine whether any species is an
endangered species or a threatened species, and expeditious progress is
being made to add qualified species to the Lists of Endangered and
Threatened Wildlife and Plants. We must publish a notice of these 12-
month findings in the Federal Register.
Regulatory Framework
Section 4 of the Act (16 U.S.C. 1533) and the implementing
regulations in title 50 of the Code of Federal Regulations set forth
the procedures for determining whether a species is an
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endangered species or a threatened species, issuing protective
regulations for threatened species, and designating critical habitat
for endangered and threatened species. The Act defines an ``endangered
species'' as a species that is in danger of extinction throughout all
or a significant portion of its range, and a ``threatened species'' as
a species that is likely to become an endangered species within the
foreseeable future throughout all or a significant portion of its
range. The Act requires that we determine whether any species is an
endangered species or a threatened species because of any of the
following factors:
(A) The present or threatened destruction, modification, or
curtailment of its habitat or range;
(B) Overutilization for commercial, recreational, scientific, or
educational purposes;
(C) Disease or predation;
(D) The inadequacy of existing regulatory mechanisms; or
(E) Other natural or manmade factors affecting its continued
existence.
These factors represent broad categories of natural or human-caused
actions or conditions that could have an effect on a species' continued
existence. In evaluating these actions and conditions, we look for
those that may have a negative effect on individuals of the species, as
well as other actions or conditions that may ameliorate any negative
effects or may have positive effects.
We use the term ``threat'' to refer in general to actions or
conditions that are known to or are reasonably likely to negatively
affect individuals of a species. The term ``threat'' includes actions
or conditions that have a direct impact on individuals (direct
impacts), as well as those that affect individuals through alteration
of their habitat or required resources (stressors). The term ``threat''
may encompass--either together or separately--the source of the action
or condition or the action or condition itself.
However, the mere identification of any threat(s) does not
necessarily mean that the species meets the statutory definition of an
``endangered species'' or a ``threatened species.'' In determining
whether a species meets either definition, we must evaluate all
identified threats by considering the species' projected response and
the effects of the threats--in light of those actions and conditions
that will ameliorate the threats--on an individual, population, and
species level. We evaluate each threat and its projected effects on the
species, then analyze the cumulative effect of all of the threats on
the species as a whole. We also consider the cumulative effect of the
threats in light of those actions and conditions that will have
positive effects on the species, such as any existing regulatory
mechanisms or conservation efforts. The Secretary determines whether
the species meets the definition of an ``endangered species'' or a
``threatened species'' only after conducting this cumulative analysis
and describing the projected effect on the species now and in the
foreseeable future.
In conducting our evaluation of the five factors provided in
section 4(a)(1) of the Act to determine whether Yucca brevifolia or Y.
jaegeriana or both species meet the definition of an endangered species
or a threatened species, we considered and thoroughly evaluated the
best scientific and commercial information available regarding the
past, present, and future stressors and threats. We reviewed the
petition, information available in our files, and other available
published and unpublished information. Our evaluation may include
information from recognized experts; Federal, State, and Tribal
governments; academic institutions; foreign governments; private
entities; and other members of the public.
A thorough review of the taxonomy, life history, ecology, and
threats to Joshua trees is presented in the SSA report (Service 2023,
entire). Based on the SSA report and information reviewed, we developed
a species assessment form for the species that contains detailed
biological information, a thorough analysis of the listing factors, a
list of literature cited, and an explanation of why we determined that
the species do not meet the Act's definition of an endangered species
or a threatened species. This supporting information can be found on
the internet at https://www.regulations.gov under Docket No. FWS-R8-ES-
2022-0165. The following is an informational summary for the findings
in this document.
Analytical Framework
The SSA report documents the results of our comprehensive
biological review of the best scientific and commercial data regarding
the status of the species, including an assessment of the potential
threats to the species. The SSA report does not represent our decision
on whether the Joshua trees warrant listing as an endangered or
threatened species under the Act. However, it does provide the
scientific basis that informs our regulatory decisions, which involve
the further application of standards within the Act and its
implementing regulations and policies.
As discussed above, we used the three conservation biology
principles of resiliency, redundancy, and representation to assess the
Joshua trees' viability (Shaffer and Stein 2000, pp. 306-311). Briefly,
resiliency is the ability of the species to withstand environmental and
demographic stochasticity (for example, wet or dry, warm or cold
years), redundancy is the ability of the species to withstand
catastrophic events (for example, droughts, large pollution events),
and representation is the ability of the species to adapt to both near-
term and long-term changes in its physical and biological environment
(for example, climate conditions, pathogens). In general, species
viability will increase with increases in resiliency, redundancy, and
representation (Smith et al. 2018, p. 306). Using these principles, we
identified the species' ecological requirements for survival and
reproduction at the individual, population, and species levels, and
described the beneficial and risk factors influencing the species'
viability.
The SSA process can be categorized into three sequential stages.
During the first stage, we evaluated the individual species' life-
history needs. The next stage involved an assessment of the historical
and current condition of the species' demographics and habitat
characteristics, including an explanation of how the species arrived at
its current condition. The final stage of the SSA involved making
predictions about the species' responses to positive and negative
environmental and anthropogenic influences. Throughout these stages, we
used the best available information to characterize viability as the
ability of a species to sustain populations in the wild over time. The
SSA report for the Joshua trees (Yucca brevifolia and Yucca
jaegeriana), January 2023, Version 2, is a summary of the information
we have assembled and reviewed, and the following is a summary of the
key results and conclusions based on the SSA report and data evaluated.
For more detailed information, please refer to the full SSA report,
which can be found at Docket FWS-R8-ES-2022-0165 on https://www.regulations.gov and at https://www.fws.gov/office/carlsbad-fish-and-wildlife/library.
Foreseeable Future
The Act does not define the term ``foreseeable future,'' which
appears in the statutory definition of ``threatened species.'' Our
implementing regulations at 50 CFR 424.11(d) set forth a
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framework for evaluating the foreseeable future on a case-by-case
basis. The term ``foreseeable future'' extends only so far into the
future as we can reasonably determine that both the future threats and
the species' responses to those threats are likely. In other words, the
foreseeable future is the period of time in which we can make reliable
predictions. ``Reliable'' does not mean ``certain''; it means
sufficient to provide a reasonable degree of confidence in the
prediction. Thus, a prediction is reliable if it is reasonable to
depend on it when making decisions.
It is not always possible or necessary to define the foreseeable
future as a particular number of years. Analysis of the foreseeable
future uses the best scientific and commercial data available and
should consider the timeframes applicable to the relevant threats and
to the species' likely responses to those threats in view of its life-
history characteristics. Data that are typically relevant to assessing
the species' biological response include species-specific factors such
as lifespan, reproductive rates or productivity, certain behaviors, and
other demographic factors.
We considered time horizons at mid-century (2040-2069) and end of
century (2070-2100) for analyzing future conditions for Joshua trees.
In the SSA report, we developed two future scenarios (Scenario I and
Scenario II) to help us understand the plausible range of threats and
their potential impacts on the two Joshua tree species and their
habitat between now and the end of the century (2070-2099). The two
scenarios differ in the amount of projected future change in habitat
loss, invasive grasses, wildfire, and drought and increased
temperatures associated with climate change. Scenario I modeled future
conditions as a continuation of current threats under warmer climate
conditions, an approximate 5.4 [deg]F (3 [deg]C) increase (RCP 4.5) in
average temperature. Scenario II modeled an increase in threats under
much warmer climate conditions, an approximate 9 [deg]F (5 [deg]C)
increase (RCP 8.5) in average temperature. When applying the best
available information to a listing context in considering what the
foreseeable future for Joshua trees is, we considered that (1) the data
sources for invasive grass cover, climate change, wildfire, and
development provide reliable information without further extrapolation
for the time period 2050-2070; (2) the species' response to projected
climate change becomes more uncertain the further out we project
because we lack information on physiological thresholds; (3) the
forecasts for occupied habitat begin to diverge around 2050 due to the
differences in RCP projections (Hawkins 2013, entire; Bamzai-Dodson and
Rangwala 2019, pp. 31 and 32); and (4) the effects of wildfire at the
end of the century depend on where wildfires occur and the time between
fires. Upon subsequent review it was determined that although there are
climate projections available that project climatically favorable and
unfavorable areas through the end of century, climate change is the
only threat where we have reliable information for that time period.
The best available science for threats to Joshua trees and the species'
response to projected climate change and wildfire supported evaluating
future conditions out to 2040-2069 when we can reliably characterize
the species' response and status, which is a key element in determining
the foreseeable future. Beyond 50 years, human decisions that affect
global greenhouse gas (GHG) emissions and the species' response to
future conditions are a major source of uncertainty (Terando et al.
2020, pp. 14-15). Therefore, for our evaluation of future condition, we
rely on the same assumptions about the extent and magnitude of threats
projected over time in Scenarios I and II of the SSA report for the
primary threats and consider an earlier time period (2040-2069) along
the trajectory projected for Scenarios I and II. The data sources and
rationale that support this decision are summarized below.
Climate change and wildfire are the primary threats driving the
future condition of Joshua trees at 2040-2069, which is consistent with
the primary threats at the end of century in the SSA. Although all the
bioclimatic models project significant losses of climatically favorable
habitat, and increased temperatures and drought associated with climate
change are generally forecasted to have negative effects, the timing
and magnitude of the species' response to climate change are not well
established. The literature, in particular bioclimatic models, provide
information on the potential timing of future climate change without
sufficient empirical data on physiological thresholds to reasonably
forecast the magnitude of the species' response or future distribution
at the end of the century (Hampe 2004, entire; Pearson and Dawson 2004,
entire; Araujo and Townsend Peterson 2012, pp. 1527, 1528; Garcia et
al. 2016, pp. 65, 69-72). We consider the bioclimatic models to provide
an initial inference or working assumption about the potential effects
of climate change to the Joshua trees based on the limited, available
information about the two species' response to climate variables (Petru
and Tielborger 2008, pp. 717, 718, 723-726; Araujo and Townsend
Peterson 2012, pp. 1527, 1528; Franks et al. 2014, entire; Garcia et
al. 2016, pp. 65, 69-72; Thompson et al. 2023, pp. 1-7). We note that
our future projections (2040-2069) are generally consistent with the
limited available empirical information about Joshua trees' response to
drought and climate change, and the stable distribution of the two
species over the last 40 to 50 years under warmer climate conditions.
Therefore, given the uncertainty of the Joshua trees' response to
future climate conditions, we did not rely solely on the bioclimatic
model results for our 2040-2069 projections of Joshua trees'
distribution.
There is high uncertainty in the timing and magnitude of the
species' responses because information about physiological thresholds
for temperature and other physiological, phenotypic (change in form or
shape), and genetic responses that may confer tolerance, local
adaption, and adaptive capacity are unknown, and the potential exists
for climate refugia in topographically diverse areas. Also, the
demographic data are not sufficiently reliable to provide an
understanding of when Joshua tree individuals or populations may begin
to respond to the effects of climatically unfavorable conditions
identified in the bioclimatic models and how long adult trees may
persist in modeled climatically unfavorable conditions at the end of
century (Thomas 2022, pers. comm; Shafer et al. 2001, p. 207). There is
limited monitoring data available for a small area of the range of
Yucca brevifolia in Joshua Tree National Park (the park represents
approximately 18 percent of the entire range for YUBR). Because we do
not have historical context to evaluate the data, it is not clear
whether the site-specific declines noted are an indication of natural
population variability in this portion of the distribution or the early
effects of climate change. The best available science indicates that
both species are long-lived (150-300 years), adapted to hot and dry
conditions, and have been exposed to a range of environmental
conditions over thousands of years. Both species continue to occupy
most of their historical ranges, despite recent increases in
temperature on the order of 1.8 [deg]F (1 [deg]C) over the last 40 to
50 years (Figure 4-1 in Service 2023, p. 31). However, we also consider
the potential loss of occupied habitat in localized
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areas within the warmest and driest portions of the ranges of both
species. Also, the best available science does not provide information
on the population dynamics and environmental thresholds for the yucca
moth species, which are the pollinators for both Joshua tree species.
Therefore, we presumed that yucca moth populations will track Joshua
tree flowering, as has been experienced in the past, and the moth will
experience similar threat effects as described for the Joshua tree
including recent site-specific declines in Joshua tree National Park.
We note the high degree of uncertainty regarding these assumptions
about the Joshua trees' and the yucca moths' responses to climate
change which introduces uncertainty into our future projections of
species' status that we cannot quantify at this time; but we have used
the best available science in developing them, as the Act requires.
In addition, there is further uncertainty the further into the
future we project potential effects to both species because future
climate projections and the rate of warming and maximum exposure
temperatures varies depending on the global emission trajectory
evaluated (e.g., RCP 4.5 compared to RCP 8.5) (Knutti and
Sedl[aacute][ccaron]ek 2013, p. 370). At the end of the century, RCP
4.5 and 8.5 project an approximate 5.4 [deg]F (3 [deg]C) and 9 [deg]F
(5 [deg]C) increase in average temperature, respectively; and the
magnitude of this difference continues to increase through time.
Therefore, most of the difference between the present climate and the
climate at 2040-2069 and beyond will be determined by decisions made by
policymakers today and during the next few years (Terando et al., 2020,
p. 15). At this time, we have little clarity on what decisions will be
made by policymakers in the next few decades. Given the long lifespan
of Joshua trees, combined with uncertainty around future policy, we
determined the climate projections and the response of Joshua trees at
the end of century time horizon were too uncertain to make reasonable,
reliable predictions of future condition. The climate models used in
the SSA project increases in average summer temperatures of
approximately 3.6-5.4 [deg]F (2-3 [deg]C) in 2040-2069, depending on
the location within the Joshua trees' range (Wang et al. 2016,
unpaginated). This temperature range is slightly less than the future
climate condition projected in Scenario I of the SSA and within the
range of variability that Joshua trees have experienced and were
resilient to in the past. Therefore, we consider the mid-century (2040-
2069) climate projections to be more reliable than end of century
projections (Hawkins 2013, entire; Bamzai-Dodson and Rangwala 2019, pp.
31 and 32).
The data sources evaluated in the SSA also allow us to make more
reliable projections of the species' response to wildfire for the time
period 2040-2069. The wildfire models used in the SSA characterized
current wildfire risk as low to moderate and are considered reliable
until 2050-2070 (Klinger 2022, pers. comm). Longer term wildfire risk
is dependent on past fire trends, specifically, where and how
frequently fires occurred. The best available data provide a range of
acreage that may burn at the end of the century but do not inform where
those wildfires might occur or how frequently occupied habitat might
burn. Therefore, we can more confidently assess the threat of wildfire
through 2070, based on currently available models. For wildfire, we
project 12 to 18 percent of the current ranges of Joshua trees to be
the maximum extent of wildfire at the end of century and we are not
able to further refine these extents; but we project the maximum extent
to be less for the time period 2040-2069. Wildfire effects on Joshua
trees are well documented, and we project effects to be the same as
analyzed in the SSA and summarized in the threat section below.
When applying the best available information to develop a
reasonable and reliable projection of the Joshua trees' future
condition, the projections of occupied Joshua trees' habitats (i.e.,
future distribution) begin to diverge around 2050 based in large part
on RCP projections. As we mentioned earlier, after 2040-2069, there is
too much uncertainty in the amount of occupied habitat based on the
variability in plausible global emissions trajectories, wildfire risk,
and the two species' responses for us to make a reliable projection of
the Joshua trees' future condition. Although our SSA report used future
scenarios that provide a range of plausible conditions projected to the
end of century, we determined that projections within the 2070-2099
timeframe did not provide a reasonable basis to reliably predict the
impact of future threats and the species' response to them due to the
identified uncertainties. Regardless of how far into the future we
could extrapolate the expanding scope of the threats, our confidence is
greatest at 2040-2069, the period over which we can make reliable
predictions about threats and the species' response to those threats.
Summary of Biological Status and Threats
In the following discussions, we review the biological condition of
the species and their resources, and threats that influence the
species' current and future conditions, to assess the species' overall
viability and the risks to that viability. In this section, we
summarize the Joshua trees' future condition to 2069 when we can
reliably forecast threats and the species' response to those threats.
This is a shorter timeframe than we evaluated future scenarios in the
SSA report. Over the next 47 years (approximately one generation and
when trees can reproduce sexually), we can reliably characterize the
Joshua trees' viability where our confidence is greatest with respect
to the range of projected plausible threats and the species' response.
There are key areas of uncertainty, primarily regarding the two
species' response to projected future wildfire and climate conditions,
that do not allow us to reliably project the Joshua trees' status to
end of century, as discussed above and in the Finding.
Threats
In the Joshua tree SSA report, we identified the following threats
for both Yucca brevifolia and Y. jaegeriana: (1) Habitat loss and
degradation (from urbanization, military training, renewable energy,
grazing, and off highway vehicle (OHV) use) (Factor A); (2) invasive
grasses (Factor A); (3) increased risk of wildfire (Factor A); (4) seed
predation and herbivory (Factor C); and (5) changing climatic trends
(e.g., increased temperatures and longer more frequent drought periods)
(Factor A). Of these threats, we determined that the primary threats or
those threats which have the capacity to potentially drive any
population or status trends for the two species are the risk of
wildfire (Factor A), invasive grasses (Factor A), and climate effects
(increasing temperature, precipitation changes, drought) (Factor A)
summarized below both currently and for the foreseeable future (2040-
2069). Because the life history, habitat needs, demographic needs,
species needs, and general ecology of the two species are congruent, we
assumed the effects pathways and threat impacts are the same for both
species. Although habitat loss and degradation (from urbanization,
military training, renewable energy, grazing, and OHV use) (Factor A)
and seed predation and herbivory (Factor C) were identified as
potential threats in the SSA report that may impact individuals or
portions of the
[[Page 14544]]
population, the best available information indicates that these threats
have not negatively influenced population dynamics on a population- or
species-level scale now and are not projected to negatively influence
population dynamics in the foreseeable future.
Overutilization (Factor B), disease (Factor C), and small
population size (Factor E) were not identified as threats in the SSA
report. In appendix B of the SSA report, we examined the existing
regulatory mechanisms, regulations, and policies (Factor D) that affect
the species, including those that relate to climate change (Service
2023, pp. 152-161). We found that the regulatory mechanisms, such as
the Clean Air Act (42 U.S.C. 7401 et seq.), which regulates air
emissions from both stationary and mobile sources, and hazardous air
pollutants to protect public health, as well as California climate
policies that help to reduce GHG emissions through the State's Climate
Adaptation and Resiliency Program (funds projects that provide climate
adaptation and resilience on California's natural and working lands),
all contribute toward reduced GHG emissions in the United States. The
National Environmental Policy Act (NEPA; 42 U.S.C. 4321 et seq.) also
provides some protections for listed species that may be affected by
activities undertaken, authorized, or funded by Federal agencies, which
may result in the development of avoidance and mitigation measures for
the threats that affect special status species. For the purposes of
this document, the primary threats are the focus of the threats
discussion for the two species which are summarized below both
currently and for the foreseeable future (2040-2069). For a complete
description of all the threats and existing regulatory mechanisms,
refer to chapter 6 and appendix B of the SSA report (Service 2023, pp.
50-87, 152-161).
Habitat Loss and Degradation
The loss of habitat and degradation by urbanization, military
training, renewable energy development, grazing, and OHV use are
occurring in varying degrees across the range of the Joshua trees and
are currently considered a low magnitude threat. The higher severity
impacts of urbanization, military training, and renewable energy
development are localized and have a limited scope in terms of acreage
of impacts and the analysis units where they occur. The YUBR South
analysis unit is most affected by habitat loss and degradation both now
and in the future due to its proximity to larger, metropolitan centers
with increased development and edge effects, along with the amount of
the analysis unit that is privately owned (45.6 percent), designated
for renewable energy development, and subject to military training.
Privately owned landownership is low (7 percent) throughout the range
of Yucca jaegeriana and is highest in YUJA East (23.5 percent). No
information was available to categorize the threat of renewable energy
development in Arizona, Nevada, and Utah. Grazing and OHV use are more
widespread, but the intensity of the impacts is currently low and
diffuse; and impacts are projected to remain low and diffuse in the
future.
The best available information indicates that substantial habitat
loss due to development, military training, or renewable energy
development is unlikely in the foreseeable future. Habitat loss due to
development was projected for 2060 based on the average of two models
available through the Integrated Climate and Land Use Scenarios (ICLUS)
database for RCP 4.5 and 8.5 (Environmental Protection Agency 2015) to
be less than 8 percent of the current distribution of Yucca brevifolia
and less than one percent of the distribution of Y. jaegeriana. In
addition, estimates include 2040-2069 projections for renewable energy
development in California for Y. brevifolia (approximately 100,000 ac;
40,469 ha), based on the acreage of current and permitted projects that
is forecasted to be approximately half the development projected for
the end of century (Service 2023, pp. 53). However, we lacked
sufficient information to project renewable energy development outside
of California. Habitat loss is forecasted to be a low-magnitude threat
in the future.
In addition, impacts to Joshua trees are avoided, minimized, or
mitigated on Federal lands and within several jurisdictions in
California to varying degrees as discussed in appendix B and section
6.1.6 of the SSA report (Service 2023, pp. 57, 152-161). We anticipate
that these measures and regulations will continue to address potential
losses in that region now and in the future, particularly on military
and federally managed lands, which currently account for 74 percent of
the current distribution of Yucca brevifolia and 89 percent of the
distribution of Y. jaegeriana (Table 4-1 in Service 2023, p. 33).
However, in Arizona, Nevada, and Utah, there are fewer regulatory
protections in place on private land, though private land in these
states represents a small percentage of the species' range. Overall,
these effects are localized and constitute a small portion of the
range, such that they are not likely to have a population- or species-
level impact. Therefore, there is no indication that current or future
effects (2040-2069) resulting from habitat loss and degradation by
urbanization, military training, renewable energy development, grazing,
or OHV use, or a combination of these, would significantly reduce the
redundancy, representation, or resiliency of Y. brevifolia or Y.
jaegeriana. See chapter 6 of the SSA report for more detailed
information (Service 2023, pp. 50-87).
Wildfire
Wildfires are not historically a common occurrence in the desert
regions of the southwestern United States. Due to the low,
discontinuous vegetative cover and fuel loads, wildfires are typically
infrequent and small in size (Brooks and Matchett 2006, p. 148). Fire
return intervals of greater than 100 years or more were estimated for
Artemisia tridentata (Great Basin sagebrush) plant communities in the
Southwest, and similar historical return intervals or longer are
presumed for the range of Joshua trees (Mensing et al. 2006, p. 75). As
a result, native scrub vegetation communities in the desert Southwest,
including Joshua trees, have not evolved with wildfire and are
generally considered to not be well-adapted to fire (Abella 2010, p.
1249). Wildfires may cause numerous potential direct and indirect
effects on Joshua trees and the associated plant community, including
immediate mortality, reduced survivorship over time, loss of nurse
plants, reduced native cover, lower native plant diversity, damage to
the protective bark-like periderm, mortality of the seed bank, and
potential disruption of the pollinator and rodent communities. Joshua
trees' habitat is estimated to require approximately 100 years to reach
densities, cover and stature similar to pre-burn conditions, though
nurse plant cover and the understory may attain pre-burn conditions in
as little as a few years to several decades depending on whether the
root crown survives (Minnich 1995, p. 104). Wildfires also promote
colonization by invasive grasses, discussed further below.
The magnitude of the impact varies with the size, severity, and
frequency of wildfires; amount of invasive grass cover; and weather
conditions both during and after the event (DeFalco et al. 2010,
entire; Barrios et al. 2017, entire; Klinger et al. 2019, p. 10).
Joshua tree mortality can be high following wildfire (64 to 95 percent)
with increased impacts to young age-classes
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and when wildfires were followed by drought conditions (Minnich 1995,
p. 102; DeFalco et al. 2010, p. 246). Habitat recovery is similarly
impacted by subsequent climate conditions and may take 100 years to
reach densities, cover, and stature similar to pre-burn conditions
(Minnich 1995, p. 104), though habitat recovery may be sooner in low
severity wildfires where individual trees persist and can reproduce
(flower and resprout) under appropriate climate conditions. Joshua
trees also may respond to wildfire by producing resprouts from the
trunk or from the primary roots (Minnich 1995, p. 102; Barrios et al.
2017, p. 103; St. Clair et al. 2022, p. 4). Resprouting requires the
tree or root system to be viable post-fire. Resprouting is more
frequent in areas with a high proportion of surviving trees and
decreases with increasing burn severity (Minnich 1995, p. 103).
Resprouting and the clonal growth strategy increases persistence of the
individual under stress, such as wildfire (Rowlands 1978, p. 50;
Harrower and Gilbert 2021, p. 11; Esque 2022a, pers. comm.), and
facilitates the ability of Joshua trees to continue to occupy habitat
even when the main stem has died. Also, within the burn perimeter,
small patches with trees, nurse plants, and a seedbank may persist to
facilitate recovery of the species and its habitat post-fire (Klinger
2022, pers. comm.).
The wildfire risk and potential impacts to Joshua trees were
characterized based on low (less than 4,000 ft; 1,200 m), middle
(4,000-6,000 ft; 1,200-1,800 m) or high (greater than 6,000 ft; 1,800
m) elevation plant communities (see table 6-1 and appendix D in the SSA
report (Service 2023, pp. 67, 165; Klinger et al. 2019, entire)). Low
elevations tend to have low severity fires due to low vegetative cover.
In areas subject to low severity fire, adult Joshua trees have a lower
probability of dying from direct mortality, and trees may avoid being
burned due to their taller stature, particularly for Yucca brevifolia.
However, repeated low severity events promoted by invasive grasses
contribute to increased charring over time that can increase the risk
of mortality, particularly to young plants that are more vulnerable to
fire. Middle elevation vegetation communities are correlated with
increasing fires, acres burned, and the invasive grass-wildfire cycle
(Brooks and Matchett 2006, pp. 153, 155). The invasive grass-fire cycle
is well documented in the literature as a positive feedback loop, and
invasive grasses alter the fire regime in several ways (discussed
further in section 6.3 of the SSA report (Service 2023, pp. 60-70)).
Middle elevations typically have a higher fuel load, with sufficient
native vegetative cover to carry fires; therefore, wildfires can be
more severe and are often associated with increased invasive grass
cover. Moderate severity burns may result in adult mortality and are
projected to char trees, including singeing the crown, which may
contribute to increased mortality and decreased tree densities over
time. In moderate severity burns, nurse plants may be burned and die,
and the Joshua tree and nurse plant seedbank may also be negatively
impacted. Though fires are less frequent in high-elevation vegetation
communities with heavier fuels, when they do occur, wildfires tend to
have higher severity and can result in direct tree mortality or alter
the subsequent vegetation composition and cover. However, most Joshua
trees occur in low and middle elevation vegetation communities that are
unlikely to experience high severity burns.
Based on the wildfire history and modeled wildfire risk, increased
wildfires are an imminent, low-to-moderate magnitude threat currently
and in the foreseeable future (2040-2069). Since 1960, only 9 percent
of the total acreage across the range of Joshua trees has burned,
including 24 percent of the YUJA North analysis unit. We project
recovery of the species and habitat to take up to 100 years in areas
that do not have an altered invasive grass-wildfire cycle. The modeled
risk of wildfires and the modeled wildfire regimes are estimated for
current and future conditions through approximately 2070 (Klinger et
al. 2021, entire). We project that the acreage of the range of both
species of Joshua tree that will burn in 2040-2069 will be less than
our end of century projections of 12 to 18 percent of the range of both
species of Joshua tree; this estimate is based on a moderate increase
in the acreage that has burned in the last 50 years (9 percent on
average), and wildfires are more likely to occur in areas that have
previously burned (Klinger 2022, pers. comm.). Although the risk of
wildfires was modeled, there is uncertainty in where wildfires will
occur, how the fire return interval will be affected, and how often
high frequency fires will occur; although increased impacts from
wildfire are projected for middle- and high-elevation plant
communities. We project the potential for tree mortality, reduced tree
densities, and limited recruitment following wildfires, while the
habitat recovers. Post-fire habitat recovery may occur more quickly in
more mesic areas; but the time required for recovery may be extended
beyond 100 years due to drought conditions.
Overall, there is limited evidence of the invasive grass-wildfire
cycle currently but it is most prevalent in the northern portion of the
range of Yucca jaegeriana. Yucca jaegeriana is also at higher risk of
wildfires due to a high proportion of the analysis units with estimated
high ignition probability, fire frequency, and burn severity. Areas of
predicted high burn severity occur near predicted high frequency
wildfire areas, increasing the probability of large wildfire events
that could impact Joshua trees. Wildfire is a low magnitude threat in
YUJA East because this area is at low elevation with lower vegetative
cover and a low probability of natural ignitions.
The risk of wildfires is a low to moderate threat throughout the
range of Yucca brevifolia and lower than for Y. jaegeriana. YUBR North
is at moderate risk for a moderate- to high-severity fire that could
alter the vegetation composition and cover in areas adjacent to higher
invasive grass cover. The probability of natural ignition is lower in
this analysis unit, but there are population centers and high areas of
visitation that are likely to increase human-caused ignitions. YUBR
South is also considered to be at moderate risk. Approximately 9
percent of the analysis unit has burned in the last 50 years, but most
of the analysis unit is at low elevation with wildfire risk
characterized by low frequency and severity. Ignition sources may be
higher than predicted in the models due to the high frequency of
wildfires along the urban-wildland interface consistent with
correlations between increasing human population density and fire
ignitions (Keely and Fotheringham 2001, p. 1541).
Under projected future climate conditions, areas previously burned
have a high probability of being colonized by invasive grasses,
particularly cheat grass in the north and northeast, and the elevation
limit of the distribution of invasive grasses may increase with
increasing temperatures and the potential for increased fire frequency.
We forecast vegetation cover to decrease at lower elevations over time
with extended droughts and increased fire frequency in previously
burned areas, particularly to the east and northeast, though extreme
rainfall events have the potential to reestablish high invasive grass
cover. Overall, we project there to be a high probability of large,
infrequent, high severity wildfires at middle and high elevations in
areas
[[Page 14546]]
that have not burned, and lower potential and frequency of wildfires at
low elevations. Small patches of unburned habitat may remain within
burned areas at middle- and high-elevation zones due to topographic
heterogeneity and hydrological refugia.
We are not able to accurately predict areas that will burn in the
future; however, we project areas that burn once at low to moderate
severity may recover slowly (up to 100 years post-burn) and continue to
support Joshua trees. We project high severity fires and areas that
burn repeatedly are not likely to support the species in the future
(Klinger 2022, pers. comm.). Both species occur mostly on Federal lands
and existing regulatory mechanisms include BMPs to help protect against
wildfire (see Conservation Measures and Existing Regulatory Mechanisms,
below, and appendix B of the SSA report (Service 2023, pp. 152-161)).
After examining the extent and impact of the risk of wildfire, we
project that wildfire conditions in 2040-2069 will be similar or
slightly increased relative to current conditions. We determined that
while this threat could occur throughout the range, our projections
indicate less than 12 to 18 percent of the ranges of the Joshua trees
may be at risk of burning by 2040-2069, including areas that have
burned previously. Due to the limited portions of the ranges that are
anticipated to burn and fire suppression efforts that are implemented
on Federal lands, the threat of wildfire would be unlikely to impact
either of the two species at a population- or species-level scale. The
threat of wildfire does not have the projected extent to drive any
declines in status trends for the two species during our evaluation
period. As a result, there is no indication that the current or future
effects of wildfire would significantly reduce the redundancy,
representation, or resiliency of Yucca brevifolia or Y. jaegeriana. See
chapter 6 of the SSA report for more detailed information (Service
2023, pp. 50-87).
Invasive Annual Grasses
Nonnative plant species, particularly invasive grasses spread by
humans and anthropogenic disturbance, have the potential to
substantially degrade desert habitats and affect the frequency of fire.
The potential effects to Joshua trees include competition,
perturbations in the natural disturbance and fire regime, plant
community composition, vegetation structure, and a microclimate shift
(Gordon 1998, p. 976). The severity of the nonnative plant invasion is
dependent on the influence of local site factors including soil type,
elevation, and disturbance history (Chambers 2000, pp. 1403-1412;
Gelbard and Belnap 2003, p. 429; Chambers et al. 2007, entire; Davies
2008, pp. 113-114; Chambers et al. 2013, entire; Davies and Hulet,
2014, pp. 1-2). Disturbed soils provide additional safe sites for weed
establishment, and the removal of the existing vegetation alleviates
resource competition and promotes the successful invasion of weeds
(Case 1990, pp. 9610, 9613-9614; Masters and Sheley 2001, p. 505; Novak
and Mack 2001, p. 115; Leonard 2007, pp. iii, 61-62; Hornbeck et al.
2019, entire). Once established, invasive grass cover can increase
rapidly in response to rainfall, particularly periods of high winter
precipitation typical of El Ni[ntilde]o oscillation events and
following wildfire (Brooks and Machett 2006, p. 149). In the future,
invasive grasses have the potential to expand their competitive edge
over native species and benefit under conditions of drought, increased
carbon dioxide concentration, extreme precipitation events, and
atmospheric nitrogen (Archer and Predick 2008, p. 25). As a result,
invasive grasses are projected to increase in the future, particularly
in disturbed or burned areas, although they may be constrained by
extended drought, with the potential to shift toward longer fire return
intervals in the most arid areas of the Mojave Desert (Comer et al.
2013, p. 7).
There are no published studies on the competitive effects of
nonnative plant species to the germination, growth, and reproduction of
the Joshua trees; however, we project competitive effects to increase
with increasing nonnative plant cover and seedlings to be the most
vulnerable life stage if they share the same root niche space and their
soil water needs are high at a time of active nonnative plant growth
and reproduction (Schwinning and Kelly 2013, pp. 888, 894; Craine and
Dybzinksi 2013, pp. 837, 839; Gioria and Osborne 2014, pp. 5-6). The
largest, potential negative effect of nonnative invasive grasses to the
Joshua trees is their contribution to wildfire risk and an altered
wildfire regime (see Wildfire, above; Brooks and Matchett 2006, p. 149;
Service 2023, pp. 60-70).
We evaluated the potential for nonnative plant species to
contribute to the risk of wildfire and an altered fire regime within
Joshua trees' habitat based on information on the abundance (in terms
of percent cover) of invasive grasses including cheatgrass (Bromus
tectorum), red brome (Bromus rubens), and other invasive grasses).
Currently, invasive grasses are present in approximately half of the
Joshua trees' habitat. We categorized 37 percent (3,539,813 ac;
1,432,511 ha) of the range as low abundance (based on the threshold of
less than 15 percent cover of invasive grasses) and 12 percent
(1,176,966 ac; 476,301 ha) of the range as high abundance (greater than
15 percent cover), based on the Bureau of Land Management (BLM) Rapid
Ecological Assessment (REA) models of potential invasive grass cover
for 2025 (Comer et al. 2013, p. 10). We defined these categories based
on several studies; although low levels of invasive grasses may
increase the risk of fire (Comer et al. 2013, p. 78), higher cover is
needed to sustain wildfires and alter the natural fire regime
consistent with our high abundance category (Link et al. 2006, pp. 114,
116). YUJA North has the greatest proportion of habitat characterized
as high abundance (30 percent), followed by YUBR North (15 percent).
Areas of high abundance of invasive grass cover tend to occur along the
interface between the Mojave and Central Basin and Range ecoregions
near the northern limit of Yucca brevifolia and Y. jaegeriana
distribution and represent 7 percent of the ranges of Joshua trees (see
figure 6-2 in the SSA report (Service 2023, p. 62)). Throughout the
range of Joshua trees, high abundance areas are located in recently
burned areas and along the urban-wildland interface (Comer et al. 2013,
p. 79).
Although invasive grasses are highly pervasive and beyond the
ability of any agency to eradicate, they and other nonnative plant
species are managed on Federal and State lands to varying degrees. In
particular, more than half of the distribution of Joshua trees occurs
on BLM land (54 percent). BLM has best management practices (BMPs) for
invasive and nonnative species that focus on the prevention of further
spread and/or establishment of these species (BLM 2008, pp. 76-77).
BMPs should be considered and applied where applicable to promote
healthy, functioning native plant communities, or to meet regulatory
requirements. BMPs include inventorying weed infestations, prioritizing
treatment areas, minimizing soil disturbance, and cleaning vehicles and
equipment (BLM 2008, pp. 76-77).
Invasive grasses are a low to moderate, pervasive, ongoing threat
that affects approximately half of the range of Joshua trees to some
degree. The severity ranges from low to moderate depending on the cover
and is highest in YUJA North and YUBR North. In the future (2040-2069),
invasive grasses are projected to expand their competitive edge over
native species and are likely to benefit under conditions of drought,
[[Page 14547]]
increased carbon dioxide concentration, extreme precipitation events,
and atmospheric nitrogen (Archer and Predick 2008, p. 25). As a result,
we predict that the threat of invasive grasses will increase, although
extended droughts have also been hypothesized to result in decreased
biomass and the potential to shift toward longer fire return intervals
in the most arid areas of the Mojave Desert (Comer et al. 2013, p. 7).
Using the BLM REA models described above, as well as modeled future
invasiveness from the same publication, minor increases in invasive
grass cover are projected for 2040-2069. Low invasive grass cover
increased by approximately 5 percent as areas with no previous invasive
grass cover become invaded; and the acreage at high risk increased by 1
percent to 13 percent of the range of Joshua trees.
After examining the extent and rangewide impact of invasive grasses
on Joshua tree, we determined that invasive grasses are a low magnitude
threat. Projected impacts are low throughout approximately 80 percent
of the Joshua trees' range where invasive grasses are not present or
occur in low abundance currently and are projected to remain at low
abundance in the future. A smaller portion of the range (approximately
12 to 13 percent) currently has or is projected to have a higher
abundance of invasive grass and moderate degree of threat affecting
these localized areas, particularly to the north and northeast in
burned habitat and along the urban interface. The effect of invasive
grasses on competition, soil moisture, and vegetation community
composition and structure is not currently influencing population- or
species-level dynamics, and we do not project effects to increase in
the future in unburned, intact habitat. This threat individually is
unlikely to drive any declines in status trends for either species in
the future except in developed or burned habitat. The contribution of
invasive grasses to the increased risk of wildfire is discussed above.
As a result, there is no indication that the current or future effects
of invasive grasses associated with competition with Joshua trees or
potential effects on habitat structure would significantly reduce the
redundancy, representation, or resiliency of Yucca brevifolia or Y.
jaegeriana. See chapter 6 of the SSA report for more detailed
information (Service 2023, pp. 50-87).
Climate Change
Temperatures have been increasing in the desert southwest for
decades; since 1950, the region experienced hotter temperatures than in
any period during the past 600 years (Garfin et al. 2014, p. 464).
Current summer temperatures (1991-2010) have increased by approximately
1[deg]C relative to historical temperatures (1961-1990) (figure 6-5 in
Service 2023, p. 72; Wang et al. 2016, unpaginated). The southwestern
United States is projected to be affected particularly severely by
prolonged drought, fewer frost days, warmer temperatures, greater water
demand by plants, and an increase in extreme weather events (Archer and
Predick 2008, pp. 23-24; Cook et al. 2015, entire; Jepson et al. 2016,
p. 49). For Yucca brevifolia and Y. jaegeriana, the main threats
associated with the current and future effects of climate change are
temperature increases (increasing maximum summer temperatures and
increasing minimum winter temperatures), changes in summer and winter
precipitation, and prolonged drought that contribute to increased
drought stress. Climate models forecast an increase in the variability
of precipitation, including the potential of high precipitation events
generally tied to El Ni[ntilde]o-Southern Oscillation and the potential
increase of prolonged drought conditions in the intervening period.
Increasing temperatures may increase moisture stress on adults,
potentially limit flowering at lower elevations, and may limit seedling
survival and establishment. The most dramatic temperature increases are
predicted to occur along the southern edge of the two species' ranges,
at lower latitudes and elevations such as in YUJA East, which is warmer
on average than the rest of the analysis units. Similarly, YUBR South
is currently experiencing higher moisture stress in areas with recent,
localized observations (from a 12-year period) of reduced recruitment
and survival, though we lack historical data to confirm a declining
trend. YUJA East is already experiencing the warmest cold season
temperatures under current conditions within its range (see section
5.1.5 in the SSA report (Service 2023, p. 44)) and is projected to be
warmer in the future, potentially resulting in reduced seedling growth
and establishment (see figure 6-5 in the SSA report (Service 2023, p.
72)). Overall, the pattern of increasing drought stress is likely to
occur across all analysis units to varying degrees depending on
elevation and latitude. Forecasted changes in climate conditions also
have the potential to influence or exacerbate other threats such as
increased risk of wildfire. See chapter 6 of the SSA report for more
detailed information (Service 2023, pp. 70-80).
We evaluated current and projected changes in climatic parameters
averaged across 13 general circulation models from the Climate Model
Intercomparison Project 6 (CMIP6) (Mahoney et al. 2003, entire)
compiled using the ClimateNA tool (version 7.21, https://climatena.ca/)
(Wang et al. 2016, entire). We also evaluated six Joshua tree-specific
bioclimatic models that forecast the degree to which the current
species' range will contain the same climate conditions for both
species in the future (2040-2069) or where parts of the species' ranges
will not support current climatic conditions, referred to as
climatically unfavorable throughout the rest of the document (Shafer et
al. 2001, entire; Dole et al. 2003, entire; Cole et al. 2011, entire;
Thomas et al. 2012, entire; Barrows and Murphy-Mariscal 2012, entire;
Sweet et al. 2019, entire). We did not thoroughly address these models
in the 2018 Joshua tree SSA report because earlier models used coarse-
scale climate data and the most recent model, using smaller-scale
climate data, was limited to a relatively small portion of the Joshua
trees' range and, at the time, we determined that the data could not be
extrapolated to the entire range due to the lack of demographic data.
Since our last review, additional bioclimatic models were evaluated
that support the earlier models. However, two of these models used
finer-scale data and identified the potential for climate refugia in
topographically diverse habitat that does not appear to have been
captured in the coarse-scale climate models. We evaluate the combined
results of these bioclimatic models below (see also table 6-3 of the
SSA report (Service 2023 p. 82)).
There is consistency across the bioclimatic models that the
southern portion of the ranges of both species and lower elevation
habitat areas may not support current climate conditions for Joshua
trees in the future. The models forecast that 66 to 88.6 percent of the
current range will be climatically unfavorable, meaning different than
the current climate conditions that Joshua trees occupy, in 2040-2069.
However, these models do not include estimates of Joshua trees' future
distribution and the best available science does not provide
physiological temperature thresholds to inform the timing and magnitude
of the species' response and when species viability may be affected, as
we discussed earlier (see Foreseeable Future, above), though we
acknowledge the potential for long-term negative effects to both
species. The best available science indicates that both
[[Page 14548]]
species are long-lived (150-300 years), adapted to hot and dry desert
conditions, and have been exposed to extreme and variable climate
conditions over thousands of years. Also, individual adult trees have
experienced a range of environmental conditions over the typical
lifespan of 100 to several hundred years. Both species also continue to
occupy most of their historical ranges, despite recent increases
(approximately 1.8 [deg]F (1 [deg]C)) in average summer temperatures
over the last 40 to 50 years (Figure 4-1 in Service 2023, p. 31).
Joshua trees are projected to experience increases in average
summer temperature of approximately 3.6-5.4 [deg]F (2-3 [deg]C) by
2040-2069, depending on the location (Wang et al. 2016, unpaginated).
These temperature ranges are anticipated to be within the range of
variability that Joshua trees have experienced in the recent past.
Therefore, we consider that the majority (approximately 90 percent) of
the current range of both species will continue to be occupied and
viable in 2040-2069 and acknowledge the potential for the localized
loss of occupied habitat in the warmest and driest portions of the
ranges of both species. In the last decade several masting events
(large flowering events where the majority of trees within a region
flower) were recorded despite recent temperature increases, even at the
southern limit of their distribution (Service 2023, p. 79); and we
project masting events to continue to occur throughout the majority of
the ranges of both species. Modeled climatically unfavorable areas,
areas projected to experience warmer and drier climate conditions than
current climate conditions, may have reduced ability to support species
needs with the potential for reduced growth, lower recruitment,
increased predation, and tree mortality that may contribute to
localized losses at low elevations and latitudes. We cannot reliably
assess or characterize the degree of reduction in these demographic
parameters; but we do assume and project that recruitment will be
reduced throughout portions of the currently occupied habitat modeled
as climatically unfavorable in 2040-2069 (66-88.6 percent) based on a
projected increase of approximately 3.6-5.4 [deg]F (2-3 [deg]C)(Barrows
and Murphy-Mariscal 2012, entire; Thomas et al. 2012, entire). We
project recruitment will be reduced relative to current conditions; we
assumed no to low recruitment for the warmest and driest portions of
the range and an increasing reliance on clonal growth to support
occupancy and viability.
The potential effects of increasing temperatures and drought on
Joshua trees' habitat are complex and are dependent on the direct
effects of future climatic conditions described above, as well as the
strength and magnitude of the interaction with their specialist
pollinators, the yucca moths, and rodent seed dispersers. In the last
decade several mast flowering events were recorded despite recent
temperature increases, even at the southern limit of their distribution
(Service 2023, p. 79), though there is a limited understanding of yucca
moth abundance during these events. Overall, the best available science
does not include information on the population dynamics and
environmental thresholds for the yucca moth species rangewide.
Therefore, we presumed that yucca moth populations will track Joshua
tree flowering, as has been experienced in the past, and will
experience similar threat effects as described for the Joshua tree. We
note that there is a high degree of uncertainty regarding these
assumptions which limits our ability to reliably project the Joshua
trees' future condition beyond 2040-2069. Prolonged drought conditions
may increase seed predation and herbivory as water and food resources
are limited; and we project that drought and drought-exacerbated seed
predation and herbivory may increase in the future. Currently there is
evidence of localized effects of predation and herbivory; but the best
available science does not support the potential for population- or
species- level effects currently or in the future. Prolonged droughts
may have the potential to reduce rodent populations due to limited
availability of water and food resources, but we have no reliable means
to evaluate future climate effects to the suite of rodents that forage
on Joshua trees nor future changes in seed dispersal. Recent mast
flowering events in the last decade appeared to satiate rodent
populations (Service 2023, p. 79); but any projections that we would
develop about the future predation and herbivory effects to Joshua
trees or future seed dispersal would be speculative.
The existing regulatory mechanisms in place help protect habitat
and provide protective measures for Joshua trees; however, few
regulations specifically address the threat of climate change (see
appendix B of the SSA report (Service 2023, pp. 152-161)). Therefore,
while existing regulatory mechanisms and current conservation efforts
may contribute to reduced GHG emissions in the United States, impacts
from climate change are forecasted to increase in the future.
The cumulative effects of climate change are complex and ongoing.
Currently, climate change is a low-to-moderate magnitude threat with
primarily localized effects on individual Joshua trees and portions of
populations; there is no indication that climate change is currently
reducing redundancy, representation, and resiliency of the Joshua
trees. There is the potential for higher magnitude effects in the
future, particularly for habitat at low elevation and latitudes along
the southern edge of the Joshua trees' ranges. Based on the best
available science we project that Joshua trees will still occupy and
maintain viability in the majority of the species' current distribution
in 2040-2069. Therefore, we project climate change over this time
period to be a low to moderate magnitude threat in the foreseeable
future with the greatest impacts at lower latitudes and elevations.
Forecasted reductions in recruitment may decrease resiliency in
portions of populations but there is no indication that climate change
will result in a reduction in redundancy and representation that would
impact the viability of the species through the years 2040-2069.
Summary of Threats
We evaluated the current threat of habitat loss and degradation,
invasive grasses, increased risk of wildfire, climate change, and
predation and herbivory within the distribution of Joshua trees,
including how threats varied by analysis unit (see table 6-4 of the SSA
report (Service 2023, p. 86)). Habitat loss and degradation is
generally focused in localized areas within the range of Joshua trees
and is currently considered a low magnitude threat overall and across
each of the analysis units, despite the intensity of impacts being
potentially severe in some localized areas. In the future, we project
the threat of habitat loss and degradation to increase, but the effects
will continue to be localized.
We consider invasive grasses to have a low-to-moderate potential
threat to degrade habitat; moderate potential threat was defined in
analysis units with approximately 12 to 13 percent of the area with
high invasive grass abundance. Our analysis indicated that there is
evidence of an invasive grass-wildfire cycle currently in the northern
range of Yucca jaegeriana. Wildfire models estimate an increase in the
frequency of wildfires to the northeast and high likelihood of more
severe fires at northern latitudes and higher elevations, although the
area anticipated
[[Page 14549]]
to burn is likely to be less than 12 to 18 percent (including areas
previously burned). Current climate conditions are warmer than
historical climate conditions and warmer climate conditions may be
increasing drought stress at lower elevations. It is not clear from the
limited monitoring data (from a 12-year period) if YUBR South, the
southernmost and warmest analysis unit, is experiencing a declining
trend caused by climatic conditions or if it is experiencing a natural
fluctuation in population. We do not have information on the effect of
warmer climate conditions and the current mega-drought in the rest of
the species' range; but masting reproductive events continue to occur
several times a decade, even in the southern portion of the ranges of
both Joshua tree species. Therefore, we consider climate change a low-
to-moderate threat. Predation and herbivory are considered a low-to-
moderate potential threat across the species' range. Several
regulations, planning documents, and management plans in place help
ameliorate the magnitude of these threats on Joshua trees and are
further described in appendix B of the SSA report (Service 2023, pp.
152-161). Cumulatively, these threats are not projected to result in
population- or species-level declines by 2040-2069, because the
majority of the range of both species is projected to remain occupied
and viable (Service 2023, figure 6-5, p. 87; Wang et al. 2016,
unpaginated).
Table 2--Summary of the Current and Future (2040-2069) Magnitude of the Threats * to Joshua Tree Based on the Scope, Intensity, Likelihood, and
Immediacy
[Service 2023, p. 51]. [This table appears in the SSA report as table 6-5 (p. 87)]
--------------------------------------------------------------------------------------------------------------------------------------------------------
Habitat loss and Predation and
Population/analysis unit degradation Invasive grasses Risk of wildfires Climate change herbivory
--------------------------------------------------------------------------------------------------------------------------------------------------------
Yucca brevifolia
--------------------------------------------------------------------------------------------------------------------------------------------------------
YUBR North........................ Low....................... Low to Moderate...... Moderate............. Low to Moderate..... Low.
YUBR South........................ Low +..................... Low.................. Moderate +........... Moderate +.......... Low to Moderate +.
YUBR Summary...................... Low....................... Low to Moderate...... Low to Moderate...... Low to Moderate..... Low to Moderate.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Yucca jaegeriana
--------------------------------------------------------------------------------------------------------------------------------------------------------
YUJA North........................ Low....................... Moderate +........... Moderate to High +... Low to Moderate..... Low.
YUJA Central...................... Low....................... Low.................. Moderate to High..... Low to Moderate..... Low.
YUJA East......................... Low....................... Low.................. Low.................. Low to Moderate..... Low.
YUJA Summary...................... Low....................... Low to Moderate...... Moderate............. Low to Moderate..... Low.
Overall Magnitude of Threat....... Low....................... Low to Moderate...... Moderate............. Low to Moderate..... Low.
--------------------------------------------------------------------------------------------------------------------------------------------------------
* Level of threat: low refers to impacts to the individuals; moderate refers to impacts affecting portions of an analysis unit; high refers to impacts
that may result in population level effects to the analysis unit.
+ Indicates those analysis units where the magnitude of the threat is the greatest.
Conservation Measures and Existing Regulatory Mechanisms
Threats may be ameliorated or reduced through the implementation of
existing regulatory mechanisms or other conservation measures that
benefit Joshua trees and their habitat. Federal agencies, State
agencies, and several local communities have adopted and implemented
laws, regulations, or ordinances and conservation measures that protect
native habitat and plants such as Joshua trees. Conservation measures
that assist in reducing or ameliorating individual threats are
discussed at the end of each of the discussions of individual threats
in this document and in the SSA report (Service 2023, appendix B, pp.
152-161).
For the Joshua trees, a high percentage of occupied habitat
includes lands conserved as open space and resource lands owned by the
Federal government, State agencies, and nonprofit organizations,
including lands covered by conservation easements, which provide a high
level of protection for the species and their habitat. Conservation is
categorized by the protected area database (USGS 2018, unpaginated) and
is based on how the lands are managed. Approximately 3 million ac (1.2
million ha; 32 percent) of habitat occupied by the Joshua trees is
fully conserved, including 23 percent of Yucca brevifolia's and 41
percent Y. jaegeriana's distribution. Considering lands that are
protected with allowable low-intensity or isolated impacts (e.g., OHV
use), the percentage increases to 75 percent, including 59 percent of
the range of Y. brevifolia and 89 percent of the range of Y.
jaegeriana. Additionally, approximately 82 percent of the land within
the distribution of Joshua trees is federally owned by the Service,
BLM, National Park Service (NPS), U.S. Forest Service (USFS), and
Department of Defense (DoD) (see tables 4-1 and 6-5 in the SSA report
(Service 2023, pp. 33, 87)).
Federal lands are less likely to be developed and each agency
follows established regulations and policies that provide for the
consideration or management of Joshua trees or their habitat, including
the following Federal regulations and policies: NEPA, Federal Land
Policy and Management Act of 1976 (43 U.S.C. 1701 et seq.), National
Forest Management Act (16 U.S.C. 1600 et seq.), Sikes Act and Sikes Act
Improvement Act of 1997 (16 U.S.C. 670 et seq.), National Park Service
Organic Act of 1916 (54 U.S.C. 100101 et seq.), Organic Administration
Act of 1897 (16 U.S.C. 475, 477-478, 479-481, and 551) and the
Multiple-Use, Sustained-Yield Act of 1960 (16 U.S.C. 528 et seq.),
Wilderness Act (16 U.S.C. 1131 et seq.), Endangered Species Act (i.e.,
protections for other listed species may benefit the Joshua tree or its
habitat), California Desert Protection Act (43 U.S.C. 1781 and 1781a),
and the Desert Renewable Energy Conservation Plan.
Joshua trees are currently addressed under the California
Environmental Quality Act and several local jurisdictions in California
have enacted specific tree ordinances for the Joshua trees. The Clean
Air Act and California climate policies that help to mitigate climate
change may also contribute to improved habitat conditions for Joshua
trees in the future (see appendix B of the
[[Page 14550]]
SSA report (Service 2023, pp. 152-161)). Though Joshua trees are not
listed under the California Endangered Species Act (CESA), Yucca
brevifolia has been considered a candidate for listing since 2020 (CDFW
2022, p. 1). As a candidate for listing under CESA, Y. brevifolia is
temporarily afforded the same protections as a State-listed endangered
or threatened species. The California Department of Fish and Wildlife
(CDFW) has since completed their Status review of the Y. brevifolia and
recommended that listing Y. brevifolia was not warranted (CDFW 2022,
entire); the issue is now with the California Fish and Game Commission
for a final decision. The Commission plans to make a final decision on
whether to list the western Joshua tree under CESA in February 2023, to
allow for additional Tribal consultation and deliberation time
(CALSPAN, 2022). If the Commission accepts CDFW's recommendation, the
Y. brevifolia would no longer be a candidate for listing under CESA.
The States of Arizona, Nevada, and Utah have no special designation
or protection for Joshua trees as a state listed species, however there
are regulations in place that limit collection of native desert plants.
In Arizona, Joshua trees are a salvage restricted native plant, as
prescribed in title 3, chapter 7, of the Arizona Revised Statutes at
section 3-903B.2., which means that a permit is required for removal/
collection (Arizona Department of Agriculture, 2016). Similarly, Joshua
trees, and all members of the Yucca genus, are protected in the State
of Nevada from commercial collection (see title 47, chapter 527, of the
Nevada Revised Statutes, at section 527.060 et seq.); commercial
removal and sale of Yucca harvested from State, county, or privately
owned land requires a permit from the Nevada State Forester Firewarden.
Cumulative and Synergistic Effects
We note that, by using the SSA framework to guide our analysis of
the scientific information reviewed and documented in the SSA report,
we have not only analyzed individual effects on the species, but we
have also analyzed their potential cumulative effects. We incorporate
the cumulative effects into our SSA analysis when we characterize the
current and future conditions of the species. To assess the current and
future condition of the species, we undertake an iterative analysis
that encompasses and incorporates the threats individually and then
accumulates and evaluates the effects of all the relevant factors that
may be influencing the species, including threats and conservation
efforts. Because the SSA framework considers not just the presence of
the factors, but to what degree they collectively influence risk to the
entire species, our assessment integrates the cumulative effects of the
factors and replaces a standalone cumulative effects analysis.
The threats acting on a species or its habitat do not typically
operate in isolation but could impact the species or its habitat in
conjunction with other threats. Individually identified threats may not
rise to a level of concern or be insignificant in nature and not
influence a decline in the species' status on the landscape. However,
combined, these threats may result in a greater overall cumulative
impact to a species or its habitat. In some cases, threats may also act
synergistically, with the resulting impact being greater than if the
threats were merely combined. These cumulative or synergistic impacts
could result in an increased reduction in individual and habitat
resource needs that may result in a loss of resiliency for a species.
For example, the severity of drought events could increase under future
climate conditions, which would further dry and stress vegetation and
potentially make vegetation more vulnerable to wildfire, and predation.
In our analysis of the threats facing Yucca brevifolia and Y.
jaegeriana, we took the potential cumulative or synergistic effects of
threats into consideration, and they are part of our discussion and
conclusions regarding each threat currently and into the future.
Current and Future Condition
To evaluate the biological status of Yucca brevifolia and Y.
jaegeriana both currently and into the future, we assess a range of
conditions to allow us to consider the species' resiliency, redundancy,
and representation. We evaluate how anthropogenic threats such as
habitat loss and degradation, invasive grasses, increased risk of
wildfire, climate change, and predation influence the resiliency,
redundancy, and representation of Joshua trees in regional analysis
units to describe the species' future viability. The viability of Y.
brevifolia and Y. jaegeriana depends on maintaining multiple
populations with sufficient redundancy and resiliency over time across
each species' distribution.
Current Condition
We assess the Joshua trees' current condition by evaluating
resiliency, representation, and redundancy. To assess current
conditions for Yucca brevifolia and Y. jaegeriana, each species' range
was divided into analysis units that are representative of the range of
biotic and abiotic features of Joshua trees' habitat. A high overall
resiliency condition score means all population needs are clearly met
and that the species in that unit is sufficiently resilient to
environmental variation in the range experienced by the species in the
recent past; a highly resilient analysis unit is unlikely to become in
danger of extinction and is more likely to contribute to species
viability. A medium overall resiliency condition score means some
habitat or demographic needs are minimally present while others may be
met in the analysis unit, but we project that the analysis unit likely
has the resiliency necessary to recover from stochastic variability.
For units with a medium overall resiliency condition score, although
occupancy may be lost in some areas, these units are unlikely to become
in danger of extinction, and the functionality of the unit is likely to
be retained and contribute to species viability. An overall low
population resiliency condition score means that one or more habitat or
demographic needs were not met, or all needs are at such low condition
that there is a higher probability that the analysis unit may be in
danger of extinction; a low resiliency analysis unit is unlikely to
contribute substantially to species viability.
Current Resiliency, Redundancy, and Representation
Resiliency is the ability of populations to respond to stochastic
variation despite the current level of threat. Based on the habitat and
demographic needs identified in the SSA report, condition categories
were defined where there was sufficient information to describe low,
moderate, and high condition (see table 7-2 in the SSA report (Service
2023, p. 92)). We identified four condition categories including
habitat quantity (availability of occupied habitat), habitat quality
(invasive grass cover), and two demographic parameters (tree density
and recruitment). The analysis units were then assessed to evaluate
population resiliency based on these categories (see table 7-3 in the
SSA report (Service 2023, p. 93)). Chapter 7 of the SSA report
describes the parameters and assessment methodology (Service 2023, pp.
87-100).
We evaluated the Joshua trees' redundancy and representation in the
context of the species' needs (see chapters 5 and 7 of the SSA report
for a description of the assessment methodology (Service 2023, pp. 41-
50,
[[Page 14551]]
87-100)). Redundancy describes the ability of a species to withstand
catastrophic events that would result in the loss of a substantial
component of the species' total overall population and can be assessed
based on the number of populations and their resiliency, distribution,
and connectivity. Representation is the ability of a species to
withstand and adapt to long-term changes in environmental conditions
(i.e., significant changes outside the range of normal year-to-year
variations). It is measured by the breadth of genetic or ecological
diversity within and among populations and is used to evaluate the
probability that a species can adapt to environmental changes.
I. Yucca brevifolia
Resiliency: Yucca brevifolia occupies a large and diverse area of
4.4 million ac (1.8 million ha) in two analysis units of similar size
within the western Mojave Desert. We consider both YUBR North and YUBR
South highly resilient due to moderate to high condition for both
habitat (e.g., quantity and quality) and demographic (e.g., tree
density and recruitment) parameters (see table 7-3 in the SSA report
(Service 2023, p. 93)). The range of Y. brevifolia is comprised of
approximately 3.3 million ac (1.3 million ha: 74 percent) of Federal
lands that are administered by the NPS, BLM, USFS, and Department of
Energy, as well as military lands. The species' distribution also
includes several National Parks (Joshua Tree National Park, Death
Valley National Park), California State Parks (Red Rock Canyon State
Park), and County parks and preserves where Joshua trees are protected
and managed. The southern analysis unit (YUBR South) has a higher
proportion of the area privately owned (45.6 percent) and potentially
subject to development, but half (52 percent) of the unit is under
Federal management. The species' distribution in this unit occurs along
a latitudinal gradient, and the southern analysis unit is currently,
and likely historically, more drought-stressed and has a higher
magnitude of threat associated with drought-exacerbated predation and
herbivory. There is recent site-specific evidence of reduced survival,
recruitment, and the availability of recruitment habitat at lower
elevations in YUBR South. However, the available data is limited both
spatially and temporally and cannot be evaluated in a historical
context; therefore, it is not clear if these data points from a 12-year
period represent natural variability or are an early indication of the
potential effects of increased temperatures and prolonged drought. We
also lack data and information on population trend and recruitment for
the rest of the species' ranges; therefore, these trends were not
extrapolated rangewide. Based on the best available data the current
demographic condition for YUBR South is moderate to high. In contrast,
YUBR North is characterized by lower temperatures and higher
precipitation, which contribute to higher recruitment condition and
moderate to high demography overall. Although there is site-specific
evidence that demographic and habitat conditions may have declined in
recent years, these changes have not been to the level that puts Joshua
trees at risk; we consider that both populations currently have a high
capacity to withstand or recover from stochastic variability due to the
large distribution, moderate to high demography, and large percentage
of the distribution conserved or managed on Federal lands. Yucca
brevifolia's resiliency is moderate-high to high throughout its range
and for all condition categories (habitat quantity, habitat quality,
tree density, and recruitment), and overall high for YUBR North and
YUBR South (see table 7-3 in the SSA report (Service 2023, p. 93)).
Redundancy: We consider Yucca brevifolia to have sufficient
redundancy to withstand catastrophic events. YUBR South and YUBR North
are spread across a very large area of mostly intact habitat that
supports resource needs and contributes to a high level of redundancy.
No range contraction has occurred over the last 30 to 40 years, based
on distribution mapping (Rowlands 1978, p. 52; Esque 2022a, pers.
comm.). The large amount of occupied habitat indicates that the range
is occupied by millions of Joshua trees distributed across a
latitudinal gradient of approximately 300 miles (mi) (483 kilometers
(km)).
Additionally, the majority of occupied habitat is located on
Federal lands--with some degree of regulatory protection, management,
and reduced probability of anthropogenic disturbance--and is less
likely to be impacted by anthropogenic development. For example, NPS
prohibits removal of Joshua trees in National Parks, actively monitors
the species, and conducts habitat restoration for the species. The risk
of catastrophic loss is very low because the species is spread across a
4.4-million-ac (1.8-million-ha) area. Across the range of Y.
brevifolia, approximately 80 percent of the occupied habitat is
characterized by a natural fire regime (i.e., fire return interval of
greater than 100 years), and greater than 50 percent of the species'
range is characterized as no or low risk from invasive grasses.
Although there is recent evidence of reduced recruitment and survival
under extreme drought conditions, these effects are documented on a
limited to relatively small area of the range; thus, we do not
anticipate that current redundancy is substantially reduced such that
wildfire, prolonged drought, or extreme predation and herbivory places
either analysis unit in danger of extinction.
Representation: We evaluated representation in Yucca brevifolia
based on the ecological diversity of the habitats it occupies, as a
surrogate for genetic diversity, and the species' life-history
characteristics that support or hinder adaptive capacity (see appendix
A in the SSA report (Service 2023, p. 150). Adaptive capacity was
evaluated following Thurman et al. 2020 (entire) to characterize Y.
brevifolia's ability to persist in place or shift in space in response
to changes in its environment. Representation, as measured by the
ecological diversity of habitats, is high for Y. brevifolia, as the two
analysis units occupy highly diverse areas within the Mojave and Great
Basin Deserts that include differences in elevation, aspect, soil type,
temperature, rainfall, and vegetation communities. The large area that
the species occupies, its broad distribution, and its ability as a
habitat generalist promote higher adaptive capacity. We do not
anticipate current site-specific reductions in recruitment to
substantially reduce abundance or representation. Across these
different environmental gradients, Y. brevifolia exhibits variability
in growth and reproductive strategies, including increased asexual
production. The clonal growth strategy increases persistence of the
individual under stress, such as wildfire (Rowlands 1978, p. 50;
Harrower and Gilbert 2021, p. 11; Esque 2022a, pers. comm.), which
along with the Joshua trees' long lifespan, facilitates the ability of
Y. brevifolia to persist in place in response to long-term or slow
changes in its environment (Thurman et al. 2020, entire). Conversely,
Joshua trees' long lifespan, limited reproductive events, long
generation time, and extended age of sexual maturity limit the ability
of Y. brevifolia to adapt to short-term changes in its environment. Its
adaptive capacity and the extent that its populations can persist in
place in the face of variable environmental conditions may also be
constrained by its obligate mutualism with the yucca moth; we do not
have information to assess the adaptive capacity of the yucca moth.
Lastly, we conclude that the species has limited
[[Page 14552]]
dispersal capabilities based on the average dispersal distances of the
rodent seed dispersers and through the absence of substantial range
expansion in the last several thousand years. Therefore, Y. brevifolia
is unlikely to be able to shift in space beyond average dispersal rates
in response to changing environmental conditions. However, the species
has other life-history characteristics that confer representation,
including high ecological variability and the capacity to persist under
similar environmental conditions as it has experienced in the past.
Although there is recent site-specific evidence of reduced recruitment
and survival under extreme drought conditions, the species currently
has the capacity to withstand and adapt to changes in environmental
conditions.
Viability: Currently, we consider Yucca brevifolia to have adequate
resiliency, redundancy, and representation throughout its range to
maintain species viability. The species' current distribution is large
(approximately 4.4 million ac (1.8 million ha)), occupies a diverse
region of topographic and ecological diversity, and spans a large
latitudinal gradient of approximately 300 mi (483 km), which
collectively confers both redundancy and representation. We consider
total abundance across the species' range to be high, although tree
densities vary and recruitment may already be reduced in the southern
portion of the range. Population resiliency is currently high in the
YUBR North and YUBR South analysis units based on the current low-to-
moderate level of threat. Drought stress at lower latitudes and
elevations due to rising temperatures and drought conditions resulting
in decreased tree vigor, mortality, reduced recruitment, and increased
herbivory and predation may impact individuals or localized areas but
are not anticipated to reduce the viability of the species.
II. Yucca jaegeriana
Resiliency: Yucca jaegeriana is distributed across a 4.9-million-
acre (1.9-million-ha) area in three analysis units across the eastern
Mojave Desert and a small portion of the southern Great Basin Desert
and western Sonoran Desert, which we consider in high condition for
habitat quantity. Approximately 89 percent of Y. jaegeriana's
distribution occurs on federally owned or managed land; private land
ownership accounts for only 7 percent of modeled habitat that primarily
occurs in YUJA East (23.5 percent). Like Y. brevifolia, Y. jaegeriana
occurs along a latitudinal gradient, and the southernmost analysis unit
is exposed to more drought stress and has the potential for higher
drought-exacerbated predation and herbivory, although we have limited
data on how prevalent this threat is in Y. jaegeriana relative to
historical conditions. YUJA North has moderate resiliency due to lower
demographic condition, although the unit has a large quantity of
occupied habitat. YUJA Central has high population resiliency despite
lower condition for habitat quality and demographic condition. YUJA
East has moderate resiliency overall, due to the smaller size of the
analysis unit and lower tree density and recruitment. Therefore, we
consider Y. jaegeriana analysis units to have moderate to high
resiliency and able to withstand environmental stochasticity (see table
7-3 in the SSA report (Service 2023, p. 93)), due to high habitat
quality and quantity associated with the large percentage of the
distribution of conserved or managed habitat on Federal lands.
Redundancy: We conclude that current redundancy is high in Yucca
jaegeriana because YUJA Central, YUJA North, and YUJA East analysis
units occur across a very large area of mostly intact habitat that
supports resource needs. No range contraction has occurred over the
last 40 years based on distribution mapping (Rowlands 1978, p. 52;
Esque 2022a, pers. comm.), though wildfire has impacted trees in
localized areas in YUJA North and YUJA Central. Additionally, plants
are located primarily on Federal lands with less probability of
development. The risk of catastrophic loss is very low because the
species is spread across a 4.9-million-acre (1.9-million-ha) area
distributed over a latitudinal gradient of approximately 300 mi (483
km) and includes potentially millions of individual trees. Despite
recent evidence of localized wildfire impacts and the invasive grass-
wildfire cycle, we conclude that current redundancy is sufficiently
high such that wildfire, prolonged drought, or extreme predation and
herbivory does not place any analysis unit of Y. jaegeriana in danger
of extinction.
Representation: We evaluated representation in Yucca jaegeriana
with respect to ecological diversity and life-history characteristics
that support or hinder adaptive capacity. Adaptive capacity was
evaluated following Thurman et al. (2020, entire) to characterize Y.
jaegeriana's ability to persist in place or shift in space in response
to changes in its environment. The large area that the species
occupies, its broad distribution, and its ability as a habitat
generalist promote higher adaptive capacity. The clonal growth strategy
increases persistence of the individual under stress, such as wildfire
(Rowlands 1978, p. 50; Harrower and Gilbert 2021, p. 11; Esque 2022a,
pers. comm.), which along with the Joshua trees' long lifespan,
facilitates the ability of Y. jaegeriana to persist in place in
response to long-term or slow changes in its environment (Thurman et
al. 2020, entire). Conversely, Joshua trees' long lifespan, limited
reproductive events, long generation time, and extended age of sexual
maturity limit the ability of Y. jaegeriana to adapt to short-term
changes in its environment. Its adaptive capacity and the extent that
its populations can persist in place in the face of variable
environmental conditions may also be constrained by its obligate
mutualism with the yucca moth; we do not have information to assess the
adaptive capacity of the yucca moth. Lastly, we conclude that the
species has limited dispersal capabilities based on the average
dispersal distances of the rodent seed dispersers and through the
absence of substantial range expansion in the last several thousand
years. Therefore, Y. jaegeriana is unlikely to be able to shift in
space beyond average dispersal rates in response to changing
environmental conditions. The species has other life-history
characteristics that confer representation, including high ecological
variability and the capacity to persist under similar environmental
conditions as it has experienced in the past. However, there is some
preliminary evidence that Y. jaegeriana's shorter stature and extensive
branching closer to the ground may make it more susceptible to wildfire
than Y. brevifolia (Cornett 2022, pp. 186-188). Ecological diversity is
high, as Y. jaegeriana occupies an extensive area covering
approximately 300 mi (483 km) from north to south and there is a high
degree of variability in abiotic and biotic conditions within these
habitats. YUJA North has high ecological diversity, as this unit is
topographically diverse with areas of low, medium, and high elevation.
Ecological variability is moderate to high both in topographic
heterogeneity and the number of ecoregions. Therefore, we consider Y.
jaegeriana to have sufficient representation to adapt to environmental
conditions over time; however, we conclude that Y. jaegeriana has
limited capacity to shift in space to overcome more rapid or extreme
variability.
Viability: Currently, we consider Yucca jaegeriana to have adequate
[[Page 14553]]
resiliency, redundancy, and representation throughout its range to
maintain species viability. The species' distribution is currently
large, approximately 4.9 million ac (1.9 million ha), and it occupies a
diverse region of topographic and ecological diversity that spans a
large latitudinal gradient of approximately 300 mi (483 km), which
confers both redundancy and representation. We characterize abundance
as low to moderate condition across the three analysis units based on
available tree density information; although tree densities vary and we
assumed them to be lower in warm environments. Population resiliency is
currently moderate to high across the three analysis units based on the
amount and quality of habitat available, and the current low to
moderate levels of threat. Although drought stress at lower latitudes
and elevations due to rising temperatures and drought conditions may be
impacting individuals or localized areas; we conclude that overall,
they do not reduce the viability of the species. Thus, the species has
sufficient viability to withstand the current level of threats.
Future Condition
In this section, we summarized the Joshua trees' future condition
to 2069 where we can reliably forecast threats and the species'
response to those threats. Over the next 47 years (approximately one
generation and when trees can reproduce sexually), we can reliably
characterize Joshua trees' viability where our confidence is greatest
with respect to the range of projected plausible threats and the
species' response. There are key areas of uncertainty, primarily
regarding the two species' responses to projected future climate
conditions, that do not allow us to reliably project the Joshua trees'
status to end of century, discussed above in Foreseeable Future and
below in the Finding. This is a shorter timeframe than we evaluated for
future scenarios in the SSA report. For our evaluation of future
condition (2040-2069), we rely on the same assumptions and data sources
about the extent and magnitude of threats projected over time in
Scenarios I and II of the SSA report for the primary threats--habitat
loss, invasive grasses, wildfire, and future climate change--
considering the time period from 2040-2069 along the trajectory
projected for Scenarios I and II. Our evaluation of future condition
summarized below considered the effects of threats individually and
cumulatively to both species of Joshua tree.
In 2040-2069, we project the two species to continue to occupy and
maintain viability in most of their current ranges, despite forecasted
temperature increases (Figure 4-1 in Service 2023, p. 31). We project
adult plant survival and persistence, and clonal growth to continue;
and the species distribution to remain similar or slightly reduced
relative to current conditions in unburned habitats across their
ranges. We project seedling recruitment will continue to occur at
reduced levels relative to current conditions due to increased drought
stress in areas modeled to be climatically unfavorable, with the
greatest reduction projected at lower elevations and latitudes. In low
and moderate severity burned habitats, we project recovery of the two
species in habitats that do not have an invasive grass-wildfire cycle,
though recovery times may take longer due to projected drought
conditions. We project localized losses of Joshua trees in developed
areas and in areas with an invasive grass-wildfire cycle. We forecast
the conditions for 2040-2069 to be similar to current conditions but
with slight reductions in resiliency from declines in recruitment, tree
density and possibly occupied habitat.
I. Yucca brevifolia
Resiliency: Based on its long persistence across large areas with
varied environmental conditions, we project that Yucca brevifolia will
continue to occupy a large and diverse area of approximately 4 million
ac (1.6 million ha) in two analysis units of similar size within the
western Mojave Desert. We project the species' distribution will
continue to occur along a latitudinal gradient, similar to its current
distribution. We project the condition of the habitat and demographic
parameters to be slightly reduced in more arid areas, including at low
elevations within the analysis unit and at lower latitude (YUBR South),
with potential localized areas of habitat loss. We consider both YUBR
North and YUBR South to be highly resilient, due to moderate to high
condition for habitat (e.g., quantity and quality) and demographic
(e.g., tree density and recruitment) parameters, and accounting for the
potential for localized reductions in recruitment and survival in YUBR
South. This species will continue to occupy habitat primarily in
Federal ownership and we project current management protections
afforded to the species will continue. The southern analysis unit (YUBR
South) has a higher proportion of privately owned land (45.6 percent)
and we project approximately 11 percent of the analysis unit may be
lost to development in low elevation areas projected to have reduced
recruitment. However, approximately 50 percent of the unit is under
Federal management and most of that area is likely to continue to
support the species in 2040-2069. YUBR South will continue to
experience more drought-stress with localized areas of reduced
recruitment and tree mortality, with a higher magnitude of threat
associated with drought-exacerbated predation and herbivory. Based on
our projections, the future demographic condition for YUBR South is
moderate and reduced from current conditions; and the analysis unit is
forecasted to maintain high resiliency in the foreseeable future. YUBR
North will continue to experience lower temperatures and higher
precipitation than YUBR South which contributes to higher recruitment
condition and high demography as well as high population resiliency.
Overall, our analysis indicated that occupancy will be maintained
throughout the range of Yucca brevifolia, and approximately 90 percent
of the current distribution will be viable in the foreseeable future
(2040-2069). We project that high resiliency for Y. brevifolia will
continue to be maintained in both analysis units; and will be similar
or slightly reduced relative to current conditions because tree
densities may be lower, and recruitment reduced. We project that these
changes in resiliency will not put the Y. brevifolia in danger of
extinction, as both analysis units are likely to be able to withstand
stochastic events and contribute to species viability.
Redundancy: We consider future redundancy in Yucca brevifolia to be
high and similar to current redundancy. YUBR South and YUBR North will
continue to occupy a very large area of mostly intact habitat that
supports the species' resource needs. We project small, localized areas
of habitat loss will occur (approximately 10 percent of the current
range) and that 90 percent of the range will maintain viability by
2040-2069. The large amount of occupied habitat indicates that the
range is occupied by millions of Joshua trees distributed across a
latitudinal gradient of approximately 300 miles (mi) (483 kilometers
(km)).
Additionally, the majority of occupied habitat will be located on
Federal lands--with some degree of regulatory protection, management,
and reduced probability of anthropogenic disturbance--and is less
likely to be impacted by anthropogenic development. The risk of
catastrophic
[[Page 14554]]
loss is very low because the species is spread across an approximately
4-million-ac (1.6-million-ha) area. Across the range of Y. brevifolia,
we project approximately 80 percent of the occupied habitat is
characterized by a natural fire regime (i.e., fire return interval of
greater than 100 years), and approximately 80 percent of the species'
range is characterized as no or low risk from invasive grasses.
Although we project reduced tree density and recruitment under extreme
drought conditions, both analysis units are forecasted to be highly
resilient. Therefore, we anticipate that future redundancy will be
sufficient to withstand catastrophic events associated with threats
(e.g., wildfire, prolonged drought, or extreme predation and
herbivory).
Representation: Representation, as measured by the ecological
diversity of habitats, remains high and we project it to be similar or
slightly reduced from current condition, as we project the two analysis
units to occupy highly diverse areas within the Mojave and Great Basin
Deserts that include differences in elevation, aspect, soil type,
temperature, rainfall, and vegetation communities. The large area that
the species occupies, its broad distribution, and its ability as a
habitat generalist promote higher adaptive capacity. We do not
anticipate projected reductions in tree density and recruitment to
substantially reduce abundance or representation. Across these
different environmental gradients, Y. brevifolia will continue to
exhibit variability in growth and reproductive strategies, including
the potential for increased asexual production to support persistence
of individuals under stress. Its adaptive capacity and the extent that
its populations can persist in place in the face of variable
environmental conditions may also be constrained by its obligate
mutualism with the yucca moth; but we were not able to reliably project
changes to this mutualism. Lastly, we project that the species'
dispersal capabilities will remain limited and similar to current
conditions. Although we project reduced tree density and recruitment,
we forecast the species to retain the capacity to withstand and adapt
to changes in environmental conditions.
Viability: Our analysis indicates that approximately 90 percent of
the current distribution will be viable in the foreseeable future
(2040-2069), though tree densities may be lower and recruitment
reduced. We predict that resiliency, redundancy, and representation for
Yucca brevifolia would continue to be viable and similar or slightly
reduced relative to current conditions. All analysis units will be
occupied, and the distribution includes a large and diverse area of
mostly intact habitat that supports resource needs and the ability to
withstand stochastic variability in environmental conditions. We
project the species to have sufficient population resiliency and the
ability to respond to stochastic and year-to-year variability. Because
Y. brevifolia is long-lived, occupies a broad distribution, is a
habitat generalist, is capable of asexual reproduction, and occupies
numerous ecological settings, we project that the species has
sufficient adaptive capacity and representation to adapt to changing
environmental conditions. Therefore, future events, such as severe
wildfire due to invasive grasses, or the effects of predation and
moisture deficit due to long-term drought and increased temperatures
due to climate changes would not lead to population- or species-level
declines that would limit species viability.
Under the range of threats forecasted, we project that Yucca
brevifolia will maintain high population resiliency. We project
redundancy to be similar to the current condition with a similar
distribution and similar population size. Our analysis indicates that
at least 90 percent (4 million ac (1.6 million ha)) of the current
distribution will be occupied. We consider this acreage and the
species' broad distribution to confer sufficient redundancy for the
species to withstand large-scale wildfires, prolonged drought, and
episodes of severe predation. No analysis unit is forecasted to be in
danger of extinction under a catastrophic event. Similarly, we project
representation to be similar or slightly reduced compared to current
conditions and that Y. brevifolia will retain adequate representation,
despite the increased risk of wildfires, increased temperatures, and
potential for prolonged drought. We considered the possibility of
potential habitat expansion in the future, but we project that it will
be limited by dispersal distance and the general lack of continuity
between currently occupied habitat and habitat forecasted to be
climatically favorable in the future. Therefore, we did not include
potential habitat expansion in our projections for resiliency,
redundancy, or representation. We project that future resiliency,
redundancy, and representation contribute to a viability that does not
place Y. brevifolia in danger of extinction.
II. Yucca jaegeriana
Resiliency: Based on its long persistence across large areas with
varied environmental conditions, we project that Yucca jaegeriana will
continue to occupy a large and diverse area of approximately 4.4
million ac (1.8 million ha) in three analysis units of similar size
within the eastern Mojave Desert, the southern Great Basin Desert, and
western Sonoran Desert. We project that the species' distribution in
the future will be similar to its current distribution along a
latitudinal gradient. We consider all three units, YUJA North, YUJA
Central, and YUJA East to be moderately resilient due to moderate to
high condition for habitat parameters (e.g., quantity and quality),
despite low to moderate demographic (e.g., tree density and
recruitment) condition projected due to the forecasted increases in
drought stress and reduced recruitment. We project the condition of the
habitat and demographic parameters to be slightly reduced in more arid
areas, including at low elevations and in the analysis unit at lower
latitude (YUJA East), with localized areas of habitat loss. We forecast
greater potential for negative impacts to YUJA East due to the
increasing temperatures and drought affecting habitat quantity, habitat
quality, and demographic parameters due to its lower latitude and
elevation. YUJA North and YUJA Central have higher but still moderate
resiliency because they occur at higher latitudes, but portions of
these analysis units also occur at lower elevation and are subject to
the increased aridity and greater effects from climate change. In
addition, these analysis units (YUJA North and YUJA Central) in the
northern portion of the range have burned, have higher invasive grass
cover, and are at increased risk of wildfire in the future with
potential impacts to both habitat and demographic parameters. This
species will continue to occupy habitat primarily in Federal ownership
and we project current management protections afforded to the species
will continue.
Overall, our analysis indicated that occupancy will be maintained
throughout the range of Yucca jaegeriana and approximately 90 percent
of the current distribution will be viable in the foreseeable future
(2040-2069). We project moderate resiliency for Y. jaegeriana in all
three analysis units that will be similar or slightly reduced relative
to current conditions because tree densities may be lower and
recruitment reduced. These changes in resiliency are not projected to
put Y. jaegeriana at risk of extinction, as all three analysis units
are likely to be able to withstand stochastic events and contribute to
species viability.
Redundancy: Future redundancy will remain high for Yucca jaegeriana
and
[[Page 14555]]
similar or slightly reduced relative to current redundancy. YUJA
Central, YUJA North, and YUJA East analysis units will continue to be
occupied and viable across a very large area of mostly intact habitat
that supports the species' resource needs. Additionally, plants are
located primarily on Federal lands with less probability of
development. The risk of catastrophic loss is very low because we
project the species to occur across an approximately 4.4-million-acre
(1.8-million-ha) area distributed over a latitudinal gradient of
approximately 300 mi (483 km) and include potentially millions of
individual trees. Despite projected wildfire impacts and the invasive
grass-wildfire cycle, we conclude that future redundancy is
sufficiently high to withstand catastrophic events associated with
wildfire, prolonged drought, or extreme predation and herbivory.
Representation: Representation, as measured by the ecological
diversity of habitats, remains high and slightly reduced from current
condition, as we project the three analysis units to occupy highly
diverse areas within the Mojave, Great Basin, and Sonoran Deserts that
include differences in elevation, aspect, soil type, temperature,
rainfall, and vegetation communities. The large area that the species
occupies, its broad distribution, and the fact that it is a habitat
generalist promotes higher adaptive capacity. We do not anticipate
reductions in tree density and recruitment to substantially reduce
abundance or representation. Across these different environmental
gradients, Yucca jaegeriana will continue to exhibit variability in
growth and reproductive strategies, including increased asexual
production to support persistence of the individual under stress. Its
adaptive capacity and the extent that its populations can persist in
place in the face of variable environmental conditions may also be
constrained by its obligate mutualism with the yucca moth; but we were
not able to reliably project changes to this mutualism. Lastly, we
project that the species' dispersal capabilities will remain limited
and similar to the current condition. Although we project reduced tree
density and recruitment, we project the species to retain the capacity
to withstand and adapt to changes in environmental conditions.
Viability: Our analysis indicates that approximately 90 percent of
the current distribution will be viable in the foreseeable future
(2040-2069), though densities of plants on the landscape may be lower
and recruitment reduced at lower latitudes and elevations. We predict
that resiliency, redundancy, and representation for Yucca jaegeriana
will continue to be maintained and will be similar or slightly reduced
relative to current conditions. All analysis units will be occupied,
and the distribution will include a large and diverse area of mostly
intact habitat that supports resource needs and the ability to
withstand stochastic variability in environmental conditions and
catastrophic events. Because Y. jaegeriana is long-lived, occupies a
broad distribution, is a habitat generalist, is capable of asexual
reproduction, and occupies numerous ecological settings, we project
that the species has sufficient adaptive capacity and representation to
adapt to changing environmental conditions. Therefore, future events,
such as severe wildfire due to nonnative grasses, or the effects of
predation and moisture deficit due to long-term drought and increased
temperatures due to climate changes in 2040-2069, would not lead to
population- or species-level declines that would limit species
viability.
Under the range of threats forecasted, we project that Yucca
jaegeriana will maintain moderate population resiliency across its
range. Redundancy is projected to be similar to or slightly reduced
relative to current condition with a similar distribution and
population size considering the potential for decreases in distribution
and population size as a result of forecasted localized loss of
occupied habitat in developed areas and at lower elevations and
latitudes. Our analysis indicates that approximately 90 percent (4.4
million ac; 1.8 million ha) of the current distribution will be
occupied and viable. We consider this acreage and the species' broad
distribution to confer sufficient redundancy for the species to
withstand potential large-scale wildfires, prolonged drought, and
episodes of severe predation. No analysis unit is projected to be in
danger of extinction due to a stochastic or catastrophic event. We
project representation to be sufficient and slightly reduced relative
to current conditions, despite the increased risk of wildfires,
increased temperatures, and potential for prolonged drought. We
considered the possibility of potential habitat expansion in the
future; but project that habitat expansion will be limited by dispersal
capability and the general lack of continuity between currently
occupied habitat and habitat forecasted to be climatically favorable in
the future. Therefore, we did not include potential habitat expansion
in our projections for resiliency, redundancy, or representation. We
project that future resiliency, redundancy, and representation will
continue to contribute to viability that does not place Y. jaegeriana
in danger of extinction.
Overall Synthesis of Future Viability
Our analyses of the threats in the future support reasonably
reliable projections of the future status of Yucca brevifolia and Y.
jaegeriana from 2040-2069. Population resiliency for both species will
be similar or slightly reduced relative to current conditions, ranging
from moderate to high. Although there is the potential for localized
habitat loss, the majority of the range of both species will continue
to be occupied and viable, including approximately 4 million ac (1.6
million ha) for Y. brevifolia and 4.4 million ac (1.8 million ha) for
Y. jaegeriana. All species needs are projected to be met throughout the
majority of the occupied habitat, including reproduction through
masting events and asexual/clonal reproduction, although recruitment
may be lower in some areas. Future resiliency is similar or slightly
reduced relative to current conditions and we project both species will
have the ability to withstand environmental stochasticity. Localized
habitat loss and reductions in recruitment are not projected to
substantially decrease redundancy and representation. Therefore, both
species are projected to have the ability to adapt to changes in
environmental conditions and be able to withstand catastrophic events.
Finding
Section 4 of the Act (16 U.S.C. 1533) and its implementing
regulations (50 CFR part 424) set forth the procedures for determining
whether a species meets the definition of an endangered species or a
threatened species. The Act defines an ``endangered species'' as a
species that is in danger of extinction throughout all or a significant
portion of its range, and a ``threatened species'' as a species that is
likely to become an endangered species within the foreseeable future
throughout all or a significant portion of its range. The Act requires
that we determine whether a species meets the definition of an
endangered species or a threatened species because of any of the
following factors:
(A) The present or threatened destruction, modification, or
curtailment of its habitat or range;
(B) Overutilization for commercial, recreational, scientific, or
educational purposes;
(C) Disease or predation;
[[Page 14556]]
(D) The inadequacy of existing regulatory mechanisms; or
(E) Other natural or manmade factors affecting its continued
existence.
Status Throughout All of Their Ranges
After evaluating threats to both of the species and assessing the
cumulative effect of the threats under the Act's section 4(a)(1)
factors, we found that while there are threats that are currently
acting on Yucca brevifolia and Y. jaegeriana such as habitat loss and
degradation (from urbanization, military training, renewable energy,
grazing, and OHV use) (Factor A), increased risk of wildfire (Factor
A), seed predation and herbivory (Factor C), invasive grasses (Factor
A), and changing climatic trends (e.g., increased temperatures and
longer more frequent drought periods) (Factor A), including cumulative
effects, we did not find that the threats are currently acting on
either of the two species at either a population- or species-level
scale such that the species are in danger of extinction throughout all
of their range. The two species are occupying most of their historical
ranges--which currently extends to over 4.4 million ac (1.8 million ha)
for Y. brevifolia and 4.9 million ac (1.9 million ha) for Y.
jaegeriana, as well as a hybrid zone of approximately 121,147 ac
(49,048 ha). We also considered the inadequacy of existing regulatory
mechanisms (Factor D) to address the primary threats to Joshua trees
from the other four factors (Factors A, B, C, and E). We found no
information to indicate that existing regulatory mechanisms (Factor D)
in combination with other threats are not helping to address the
effects of the threats to the species or would negatively affect the
status of the species. Furthermore, as discussed above, we found
various Federal and State regulatory mechanisms do currently exist that
do provide some level of protection for Joshua trees and their habitat.
Current population resiliency is high for Yucca brevifolia due to
the large amounts of moderate- to high-quality habitat occupied by the
species, as well as moderate to high tree density and recruitment
observed throughout the range. The high level of population resiliency
indicates that habitat and demographic resource needs are not limiting,
and the species is currently able to withstand stochastic events.
Similarly, current population resiliency ranges from moderate to high
for Y. jaegeriana. Although there is also a large amount of habitat
occupied by the species, the quality of habitat, tree density, and
recruitment are reduced due in part to recent wildfires and higher
levels of invasive grass cover within burned habitat, particularly in
the northern portion of its range. However, all analysis units of Y.
brevifolia and Y. jaegeriana currently retain resiliency sufficient to
withstand stochastic variability because of the quantity of moderate-
to high-condition habitat occupied by both species.
While warming and drying climate conditions have been observed,
there is no evidence to support substantial population size reductions
and range contraction over the last 40 years based on distribution
mapping (Rowlands 1978, p. 52; Esque 2022b, pers. comm.). Overall,
recruitment of both Yucca brevifolia and Y. jaegeriana is currently
occurring across their respective ranges; although we acknowledge the
potential for recent, small, and localized declines along the southern
limit of Y. brevifolia in Joshua Tree National Park, the data does not
support a population decline. The large area that the two species
occupy, the broad latitudinal distribution, and the fact that they are
habitat generalists promote higher adaptive capacity and
representation. Current reductions in recruitment are not anticipated
to reduce abundance or representation to the extent of limiting
viability. Yucca brevifolia and Y. jaegeriana exhibit variability in
density and reproductive strategies across these different
environmental gradients, including the relative proportion of asexual
reproduction. The clonal growth strategy increases persistence of the
individual under stress (e.g., wildfire), which along with the Joshua
trees' long lifespan, is anticipated to facilitate the ability of Y.
brevifolia and Y. jaegeriana to continue to occur in place in response
to long-term or slow changes in its environment. Additionally, Joshua
trees are located primarily on Federal lands, which inherently have
less pressure from anthropogenic development and often provide for
management of the species. Potential adverse impacts to both species
are dispersed across their ranges in large, occupied areas that span
millions of acres across a latitude gradient of approximately 300 mi
(483 km). This broad distribution and high number of individuals
occupying the landscape provides redundancy to withstand catastrophic
events (e.g. wildfire; Factor A) such that these events are not likely
to place any population of Y. brevifolia or Y. jaegeriana in danger of
extinction. In addition to the existing regulatory mechanisms already
in place, several Federal, State, and county agencies have been
implementing conservation measures through best management practices
specific to the Joshua trees (Y. brevifolia and Y. jaegeriana), to
protect and help sustain the species and their habitats where possible.
The net effect of current and predictable threats to the species, after
considering applicable conservation measures and existing regulatory
mechanisms, is not sufficient to cause the species to meet the
definition of an endangered species. Thus, after assessing the best
available information, we have determined that Joshua trees (Y.
brevifolia and Y. jaegeriana) are not currently in danger of extinction
throughout all of their ranges.
Therefore, we proceed with determining whether Joshua trees (Yucca
brevifolia or Y. jaegeriana) are likely to become endangered within the
foreseeable future throughout their ranges. The two species face a
variety of future threats, including the threats of habitat loss and
degradation (from urbanization, military training, renewable energy,
livestock grazing, and OHV use) (Factor A), increased risk of wildfire
(Factor A), seed predation and herbivory (Factor C), invasive grasses
(Factor A), and changing climatic trends, (e.g., increased temperatures
and longer more frequent drought periods) (Factor A) that have the
potential to reduce the viability of the two species. Of these threats,
the primary future threats are the risk of wildfire (Factor A),
invasive grasses (Factor A), and climate effects (increasing
temperature, precipitation changes, drought) (Factor A). In the SSA
report, we evaluated environmental conditions and primary threat
factors acting on the two species and developed two future scenarios
projecting to end of century to assist in determining the range of
potential future conditions.
We examined the best available data that allow predictions into the
future which extends as far as those predictions are sufficiently
reliable to provide a reasonable degree of confidence. Many available
data sources for the threats evaluated provided specific projections
out 30 to 50 years. We based our analysis on future projections of
habitat loss (including renewable energy development, invasive grass
cover, climate change, and wildfire) and the potential impacts of those
changes to species needs and habitat conditions. For example, invasive
grass cover was modeled to 2050 (Comer et al. 2013, Figure 2). Wildfire
modeling was based on current conditions and is considered accurate for
the next 30 to 50 years (Klinger 2022, pers. comm.), and development
and habitat loss projections are available to 2060 (Environmental
Protection Agency
[[Page 14557]]
2015, entire). The climate change analysis considered bioclimatic
models that provided projections for 2040-2069 (Thomas et al. 2012,
entire; Barrows and Murphy-Mariscal 2012, entire).
Future climate projections for RCP 4.5 and 8.5 and the associated
species response are more similar at 2050 and begin to diverge after
2050 based on the different socio-economic and mitigation assumptions
included in each RCP. Joshua trees' exposure to climatically
unfavorable conditions and the species' response is also more tractable
over a shorter time period, which provides greater certainty related to
threats and the species' responses to those threats, as discussed
below. We determined the climate projections and the response of Joshua
trees at the end of century time horizon were too uncertain to rely on
to analyze future condition. There is a high degree of variability in
future climate forecasts depending on the global emission scenario
evaluated at the end of the century and the magnitude of the forecasted
temperature increase diverge after 2050. There is also a high degree of
uncertainty in the timing and magnitude of the species' response to
climatically unfavorable conditions at the end of the century. As a
result, it is not clear how and when Joshua tree individuals or
populations may begin to experience the effects of climatically
unfavorable conditions, including when reduced recruitment may affect
species viability, how long adult trees may persist in climatically
unfavorable conditions, and what the physiological thresholds are for
the species (Thomas 2022, pers. comm; Shafer et al. 2001, p. 207).
We determined that the best available science regarding the status
of the species only supports reliable projections to 2040-2069. It was
noted that beyond 50 years, human decisions that affect global GHG
emissions are a major source of uncertainty (Terando et al. 2020, pp.
14-15). Although our SSA report captured the best available information
on all key influences and the future scenarios provided a range of
plausible conditions projected to the end of century, we determined
that using 2040-2069 as the foreseeable future for these listing
determinations is more appropriate considering the uncertainties
identified above and our ability to reliably predict threats and the
species' response.
In the foreseeable future (2040-2069), we predict that resiliency,
redundancy, and representation for Yucca brevifolia and Y. jaegeriana
would continue to be maintained in all analysis units. Because the two
species are long-lived, occupy broad distributions, are habitat
generalists, are capable of asexual reproduction, and occupy numerous
ecological settings, we determined that future stochastic variability
and catastrophic events, such as severe wildfire due to invasive
grasses, or the effects of predation and moisture deficit due to long-
term drought and increased temperatures due to climate changes, would
not lead to population- or species-level declines that would limit
species viability or persistence. Therefore, in 2040-2069, both species
are likely to maintain occupancy throughout each analysis unit, within
a distribution that is similar to or slightly reduced relative to
current conditions. As a result, each Joshua tree analysis unit is
likely to contribute representation and redundancy for species
viability. In addition, most of the habitat occupied by Joshua trees
occurs on Federal land with existing regulatory mechanisms in place.
Several Federal, State, and county agencies have been implementing
conservation measures through BMPs, specific to the Joshua trees (Y.
brevifolia and Y. jaegeriana), to protect and help sustain the species
and its habitat where possible and into the future. The net effect of
predictable future threats to the species, after considering applicable
conservation measures and the existing regulatory mechanisms, is not
sufficient to cause the species to meet the definition of a threatened
species. Thus, after assessing the best available information, we have
determined that Y. brevifolia and Y. jaegeriana are not likely to
become endangered within the foreseeable future throughout all of their
ranges.
Status Throughout a Significant Portion of Its Range
Under the Act and our implementing regulations, a species may
warrant listing if it is in danger of extinction or likely to become so
in the foreseeable future throughout all or a significant portion of
its range. Having determined that the two species of Joshua tree are
not in danger of extinction or likely to become so in the foreseeable
future throughout all of their ranges, we now consider whether they may
be in danger of extinction or likely to become so in the foreseeable
future in a significant portion of their ranges--that is, whether there
is any portion of the species' ranges for which it is true that both
(1) the portion is significant; and (2) the species is in danger of
extinction now or likely to become so in the foreseeable future in that
portion. Depending on the case, it might be more efficient for us to
address the ``significance'' question or the ``status'' question first.
We can choose to address either question first. Regardless of which
question we address first, if we reach a negative answer with respect
to the first question that we address, we do not need to evaluate the
other question for that portion of the species' range.
In undertaking this analysis for Joshua trees, we chose to address
the status question first. We began by identifying any portions of the
species' ranges where the biological status of the species may be
different from its biological status elsewhere in its range. For this
purpose, we considered information pertaining to the geographic
distribution of (a) individuals of the species, (b) the threats that
the species face, and (c) the resiliency condition of populations.
We evaluated the range of both Joshua tree species to determine if
either of the species is in danger of extinction now or likely to
become so in the foreseeable future in any portion of its range. The
range of a species can be divided into portions in an infinite number
of ways. We focused our analysis on portions of the species' range that
may meet the definition of an endangered species or a threatened
species. For both Joshua tree species, we considered whether the
threats or their effects on the species are greater in any biologically
meaningful portion of the species' range than in other portions such
that the species is in danger of extinction now or likely to become so
in the foreseeable future in that portion. We examined the following
threats on both species: habitat loss and degradation (from
urbanization, military training, renewable energy, grazing, and OHV
use), invasive grasses, increased risk of wildfire, changing climatic
trends (e.g., increased temperatures and longer more frequent drought
periods), and seed predation and herbivory, including cumulative
effects. As noted above, we defined foreseeable future as 2040-2069,
the time period for which we can reliably predict the threats and the
species' response to the threats.
I. Yucca brevifolia
Yucca brevifolia occupies two distinct areas, which we have
identified as a northern analysis unit (YUBR North) and a southern
analysis unit (YUBR South). As discussed in our rangewide analysis, the
threats of habitat loss and degradation (from urbanization, military
training, renewable energy, grazing, and OHV use), invasive grasses,
increased risk of wildfire, changing climatic trends (e.g., increased
temperatures and longer more frequent drought periods), and seed
predation and herbivory are known to negatively affect the YUBR North
and YUBR South analysis units,
[[Page 14558]]
currently and into the future. All these threats are rangewide, meaning
that they are acting throughout the species' range across all analysis
units. We identified areas that may have a concentration of threats,
including threats with the largest potential impacts to the species,
which may be occurring on a biologically meaningful scale. The
concentration of threats is more likely to result from increased
temperatures and drought associated with projected climate change
(modeled areas of climatically unfavorable habitat), increased risk of
wildfire, and associated habitat loss in the future. These threats
occur throughout the YUBR North and YUBR South analysis units to
varying degrees, but have the highest potential impact to the species
in the lower elevation habitat areas generally defined as less than
1,200 m. Therefore, we determined that there may be a geographical
concentration of threats due to the combination of climate change, risk
of wildfire, and habitat loss in lower elevation habitat both now and
in the future.
Approximately 66 to 88.6 percent of the range of Yucca brevifolia
is projected to be climatically unfavorable between 2040 and 2069.
While modeling predicts a large decline in climatically favorable
habitat, we project that habitat loss will be localized in these
modeled areas due to uncertainties in the species' response and because
modeled climatically unfavorable habitat does not equate to an
immediate loss of occupied habitat or a potential range contraction
between 2040 and 2069 (Shafer et al. 2001, p. 207). The potential
species' response is greatest at lower elevation areas that are
currently experiencing higher levels of drought stress with a projected
increase in aridity in the foreseeable future. Although there is a low
probability of natural wildfire ignitions and low frequency of
wildfires projected for lower elevation areas, habitat recovery post-
fire may be further hindered in these lower elevation zones under
drought conditions, and human-induced ignitions are projected to be
higher in YUBR South along the urban-wildland interface. In addition,
habitat loss due to urbanization and renewable energy development is
likely to occur in the level terrain that occurs at lower elevation in
localized areas projected to have reduced recruitment and survival,
particularly in YUBR South. The effects of these threats on the YUBR
North and YUBR South analysis units are discussed further above (see
Threats).
We next examined the status of the low-elevation areas of the YUBR
North and YUBR South analysis units, either in total (41 percent of the
species range) or within each analysis unit (5 and 74 percent
respectively) by examining the species' response at low elevation and
the resiliency, redundancy, and representation of Yucca brevifolia in
these portions. As we evaluate effects to the species in the
foreseeable future, the cumulative threats at low elevation may result
in reduced growth and recruitment, with the potential for localized
tree mortality and thinning across the low-elevation areas. We forecast
asexual reproduction to be maintained, particularly when trees are
stressed by drought or in response to wildfire, which supports the
persistence of the species at low elevations. We project habitat loss
to be localized, including in a small proportion of the low-elevation
habitat area. Therefore, Joshua trees are projected to maintain
viability throughout the majority of the habitat in each analysis unit
at low elevations into the foreseeable future.
Population resiliency at low elevations is projected to decrease
slightly relative to current conditions, including the potential for
reduced tree densities and recruitment, but is projected to be moderate
overall because of the large quantity of occupied habitat and moderate
to high habitat quality. As such, the species will continue to be able
to withstand stochastic events and normal year-to-year variation in
environmental conditions within low-elevation areas. In the foreseeable
future, forecasted tree mortality and localized habitat loss may reduce
abundance but are not anticipated to result in range contractions or
cause the species to be more vulnerable to catastrophic events such as
prolonged drought and wildfire. As a result, redundancy would be
maintained in low-elevation areas. Similarly, the species' latitudinal
range is projected to be maintained, and no substantial losses of
ecological diversity are forecasted at low elevations; therefore,
representation would be minimally impacted.
In the foreseeable future, we forecast that the species will
continue to occupy habitat in lower elevation areas, even in the more
southern latitudes of Yucca brevifolia's range, where models
consistently predict a loss of climatically favorable habitat (YUBR
South). We project that asexual and sexual reproduction will occur
throughout all analysis units and that ecological diversity will be
maintained at low elevations. Therefore, resiliency, redundancy, and
representation for the species would continue to be maintained in the
lower elevation areas of both analysis units despite the concentration
of threats in these areas. Overall, the species will continue to
maintain viability in the foreseeable future within the low-elevation
areas of each analysis unit, despite the potential for projected
reductions in demographic measures (tree density and reduced
recruitment) resulting from all the threats, but particularly from
changing climatic trends, wildfire, urbanization, and renewable energy
development threats, which will be more concentrated in the lower
elevation areas.
The best scientific and commercial information available indicates
that in the lower elevations of YUBR North and YUBR South analysis
units, Yucca brevifolia does not have a different status from its
rangewide status, so there are no portions of the species' range that
meet the Act's definition of an endangered species or a threatened
species. Therefore, we do not need to consider whether any portions are
significant.
II. Yucca jaegeriana
Yucca jaegeriana occupies three distinct areas, which we have
identified as a northern analysis unit (YUJA North), a central analysis
unit (YUJA Central), and an eastern analysis unit (YUJA East). As
discussed in our rangewide analyses, the threats of habitat loss and
degradation (from urbanization, military training, renewable energy,
grazing, and OHV use), invasive grasses, increased risk of wildfire,
changing climatic trends (e.g., increased temperatures and longer more
frequent drought periods), and seed predation and herbivory are known
to negatively affect the YUJA North, YUJA Central, and YUJA East
analysis units, currently and into the future. All these threats are
rangewide, meaning that they are acting throughout the species' range
across all analysis units. We have identified areas that may have a
concentration of threats, including threats with the largest potential
impact to the species, which may be occurring at a biologically
meaningful scale. This is more likely to result from increased risk of
invasive grasses and associated wildfire, increased temperatures and
drought associated with projected climate change in the future (modeled
areas of climatically unfavorable habitat), and habitat loss from
urbanization and renewable energy development. These threats occur
throughout the range to varying degrees but have the highest magnitude
impact and potential species' response in the lower elevation habitat
areas (generally defined as less than 1,200 m). Therefore, we
determined that there may be a geographical concentration of threats
[[Page 14559]]
due to the combination of climate change, risk of wildfire, and habitat
loss in lower elevation habitat both now and in the future.
Approximately 66 to 88.6 percent of the range of Yucca jaegeriana
is projected to be climatically unfavorable in the foreseeable future.
Although we do not forecast that climatically unfavorable habitat will
translate to the loss of occupied habitat due to the magnitude of the
temperature increases forecasted and the timeframe over which the
species is exposed to climatically unfavorable conditions, the
potential species' response is greatest in lower elevation areas. Low
elevation areas are currently experiencing higher levels of drought
stress with a projected increase in aridity in the foreseeable future.
There is a higher probability of natural wildfire ignitions in YUJA
North and YUJA Central due to lightning associated with monsoonal storm
events. The frequency of wildfires is projected to be higher at lower
elevation areas, including in portions that have burned recently and
have higher invasive grass cover. Although fire severity will be lower
at low elevations, habitat recovery post-fire may be further hindered
in the future due to drought stress, such as in YUJA East, which occurs
at both lower elevation and latitude. In addition, habitat loss due to
urbanization is likely to occur in the level terrain that occurs at
lower elevation, particularly in YUJA East. Approximately 23.5 percent
of the analysis unit is under private land ownership (Service 2023, p.
37), but less than 1 percent of the area of the analysis unit is
anticipated for further development in the foreseeable future. The
effects of these threats on the YUJA North, YUJA Central, and YUJA East
analysis units are discussed further above (see Threats).
We next examined the status in the low-elevation areas in the YUJA
North, YUJA Central, and YUJA East analysis units, either in total (60
percent of the species range) or within each analysis unit (56, 51, and
98 percent, respectively), by examining the species' response at low
elevation and the resiliency, redundancy, and representation of Yucca
jaegeriana in these portions. As we evaluate effects to the species in
the foreseeable future (2040-2069), the cumulative threats at low
elevation may result in reduced growth and recruitment, with the
potential for tree mortality and thinning across the low-elevation
areas. We forecast asexual reproduction to be maintained, particularly
when trees are stressed by drought or in response to wildfire, that
will support the persistence of the species at low elevations. We
project habitat loss to be localized, including in a small proportion
of the low-elevation habitat area. Therefore, Joshua trees are
projected to maintain viability throughout the majority of the habitat
in each analysis unit at low elevations into the foreseeable future as
defined.
Population resiliency at low elevations is projected to decrease
slightly relative to current conditions, including the potential for
reduced tree densities and recruitment, but is projected to be moderate
overall because of the large quantity of occupied habitat and moderate
habitat quality. As such, the species will continue to be able to
withstand stochastic events and normal year-to-year variation in
environmental conditions within the low-elevation areas. In the
foreseeable future, forecasted tree loss and localized habitat loss may
reduce abundance; but are not anticipated to result in range
contractions or cause the species to be more vulnerable to catastrophic
events such as prolonged drought and wildfire. As a result, redundancy
would be maintained in the low-elevation areas. Similarly, the species'
latitudinal range is projected to be maintained in 2040-2069, and no
substantial losses of ecological diversity or potential arid-adapted
genotypes are forecasted at low elevations; therefore, representation
would be minimally impacted.
In the foreseeable future, we forecast that the species will
continue to occupy habitat in lower elevation areas, even in the more
southern latitudes of Yucca jaegeriana's range where models
consistently predict a decline in climatically favorable habitat (YUJA
East). We project that asexual and sexual reproduction will occur
throughout all analysis units and that ecological diversity will be
maintained at low elevations. Therefore, resiliency, redundancy, and
representation for the species would continue to be maintained in the
lower elevation areas of all analysis units despite the concentration
of threats in these areas. Overall, the species will continue to
maintain viability in the foreseeable future within the low-elevation
areas of each analysis unit, despite the potential for projected
reductions in demographic measures (range thinning and reduced
recruitment) resulting from all the threats, but particularly from
changing climatic trends, wildfire, invasive grasses, and urbanization
threats, which will be more concentrated in the lower elevation areas.
The best scientific and commercial information available indicates
that in the lower elevations of the YUJA North, YUJA Central, and YUJA
East analysis units, Yucca jaegeriana does not have a different status
from its rangewide status, so there are no portions of the species'
range that meet the Act's definition of an endangered species or a
threatened species. Therefore, we do not need to consider whether any
portions are significant.
Therefore, we find that Yucca brevifolia and Y. jaegeriana are not
in danger of extinction now or likely to become so in the foreseeable
future in any significant portion of their ranges. This does not
conflict with the courts' holdings in Desert Survivors v. Department of
the Interior, 321 F. Supp. 3d 1011, 1070-74 (N.D. Cal. 2018), and
Center for Biological Diversity v. Jewell, 248 F. Supp. 3d 946, 959 (D.
Ariz. 2017) because, in reaching this conclusion, we did not apply the
aspects of the Final Policy on Interpretation of the Phrase
``Significant Portion of Its Range'' in the Endangered Species Act's
Definitions of ``Endangered Species'' and ``Threatened Species'' (79 FR
37578; July 1, 2014), including the definition of ``significant'' that
those court decisions held to be invalid.
Determination of Status
Our review of the best available scientific and commercial
information indicates that Yucca brevifolia and Y. jaegeriana do not
meet the definition of an endangered species or a threatened species in
accordance with sections 3(6) and 3(20) of the Act. Therefore, we find
that listing either of the Joshua tree species is not warranted at this
time. Further discussion of the basis for these findings can be found
in the Joshua trees' species assessment form, the revised SSA report
(Service 2023, entire), and other supporting documents (see ADDRESSES,
above) that capture the scientific information upon which our decision
was based.
New Information
We request that you submit any new information concerning the
taxonomy of, biology of, ecology of, status of, or stressors to Joshua
trees (Yucca jaegeriana or Y. brevifolia) to the person listed above
under FOR FURTHER INFORMATION CONTACT, whenever it becomes available.
New information will help us monitor these species and make appropriate
decisions about their conservation and status. We encourage local
agencies and stakeholders to continue cooperative monitoring and
conservation efforts.
References Cited
A list of the references cited in this document is available on the
internet at
[[Page 14560]]
https://www.regulations.gov under Docket No. FWS-R8-ES-2022-0165 in the
species assessment form, or upon request from the person listed above
under FOR FURTHER INFORMATION CONTACT.
Authors
The primary authors of this document are the staff members of the
Species Assessment Team, Ecological Services Program.
Authority
The authority for this action is section 4 of the Endangered
Species Act of 1973, as amended (16 U.S.C. 1531 et seq.).
Martha Williams,
Director, U.S. Fish and Wildlife Service.
[FR Doc. 2023-04680 Filed 3-8-23; 8:45 am]
BILLING CODE 4333-15-P