[Federal Register: June 4, 2004 (Volume 69, Number 108)]
[Rules and Regulations]
[Page 31523-31531]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr04jn04-8]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
Endangered and Threatened Wildlife and Plants; 12-Month Finding
for a Petition to Delist Astragalus magdalenae var. peirsonii
(Peirson's Milk-vetch)
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Notice of 12-month petition finding.
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SUMMARY: We, the U.S. Fish and Wildlife Service (Service) announce a
12-month finding for a petition to delist Astragalus magdalenae var.
peirsonii (Peirson's milk-vetch) under the Endangered Species Act (Act)
of 1973, as amended, (16 U.S.C. 1531 et seq.). After reviewing the best
scientific and commercial information available, we find that the
petitioned action is not warranted. We ask the public to submit to us
any new information that becomes available concerning the status of, or
threats to, the species. This information will help us monitor and
encourage the conservation of this species.
DATES: The finding announced in this document was made on May 28, 2004.
Although no further action will result from this finding, we request
that you submit new information concerning the status of, or threats
to, this species, whenever it becomes available.
ADDRESSES: The complete file for this finding is available for
inspection, by appointment, during normal business hours, at Carlsbad
Fish and Wildlife Office, U.S. Fish and Wildlife Service, 6010 Hidden
Valley Road, Carlsbad, California 92009. Submit new information,
materials, comments, or questions concerning this plant to us at the
above address.
FOR FURTHER INFORMATION CONTACT: Jim Bartel, Field Supervisor, Carlsbad
Fish
[[Page 31524]]
and Wildlife Office; telephone (760-431-9440).
SUPPLEMENTARY INFORMATION:
Background
Section 4(b)(3)(B) of the Act requires that within 12 months after
receiving a petition to revise the List of Threatened and Endangered
Species that contains substantial information indicating that the
petitioned action may be warranted, the Secretary shall make one of the
following findings: (a) The petitioned action is not warranted, (b) the
petitioned action is warranted, or (c) the petitioned action is
warranted but precluded by pending proposals. Such 12-month findings
are to be published promptly in the Federal Register.
The Peirson's milk-vetch was listed as threatened on October 6,
1998 (63 FR 53596). At the time of listing, the primary threat to the
milk-vetch was the destruction of individuals and dune habitat from
off-highway vehicle (OHV) use and the recreational development
associated with it. On October 25, 2001, we received a petition to
delist Astragalus magdalenae var. peirsonii dated October 24, 2001,
from David P. Hubbard, Ted J. Griswold, and Philip J. Giacinti, Jr. of
Procopio, Cory, Hargreaves & Savitch, LLP, that was prepared for the
American Sand Association (ASA), the San Diego Off-Road Coalition, and
the Off-Road Business Association (ASA et al. 2001). On September 5,
2003, we announced an initial petition finding in the Federal Register
that the petition presented substantial information to indicate the
petitioned action may be warranted (68 FR 52782). In accordance with
section 4(b)(3)(A) of the Act, we have now completed a status review of
the best available scientific and commercial information on the
species, and have reached a determination regarding the petitioned
action. This determination meets deadline requirements established by a
court-approved settlement agreement (ASA et. al. v. USFWS and Gale
Norton, Stipulated Settlement Agreement, Civ. No. 03-315L LAB).
Species Description
Astragalus magdalenae var. peirsonii is an erect to spreading,
herbaceous, short-lived perennial in the Fabaceae (Pea family) (Barneby
1959, 1964). Plants may reach 8 to 27 inches (20 to 70 centimeters) in
height and develop taproots (Barneby 1964) that penetrate to the
deeper, moister sand. According to Phillips and Kennedy (2003), plants
largely die back to a root crown in the summer. The stems and leaves
are covered with fine, silky appressed hairs. Young seedlings often
retain their cotyledons (Phillips and Kennedy 2003). The leaflets,
which may fall off in response to drought, are small and widely spaced,
giving the plants a brushy appearance. This taxon is unusual in that
the terminal leaflet is continuous with the rachis rather than
articulated with it. The purple flowers are arranged in 10- to 17-
flowered axillary racemes. Romspert and Burk (1979) found
inflorescences present from December through at least April. Astragalus
lentiginosus var. borreganus, easily distinguished by its conspicuously
broad leaflets, and Astragalus insularis var. harwoodii, easily
distinguished by its smaller stature and shorter banner petals, are the
only other Astragalus taxa found nearby.
Life History
Astragalus magdalenae var. peirsonii has variously been considered
an annual or perennial (Munz 1932, 1974; Barneby 1959, 1964;
Spellenberg 1993; Willoughby 2001). Willoughby (2001) states that A. m.
var. peirsonii apparently is a short-lived perennial, and as such its
response to rainfall was predictable. Documented persistence of
individuals also attests to the perennial nature of A. m. var.
peirsonii (Phillips and Kennedy 2002, 2003). The onset of germination
may occur anytime between the beginning of January and the end of
February (Porter in litt. 2003b). Plants are reportedly in flower from
as early as mid-November through May (Barneby 1965; Porter in litt.
2003b; Phillips and Kennedy 2002).
As part of his studies of the natural history and pollination
biology of Astragalus magdalenae var. peirsonii, Porter (in litt.
2002a) has identified a white-faced, medium-sized, solitary bee as the
only effective pollinator. His preliminary experiments in the field and
under greenhouse conditions indicate that A. m. var. peirsonii plants
are not capable of self-pollination in the absence of pollinators. This
is a significant consideration for population structure and function.
Large populations of standing individuals are likely necessary to
provide adequate numbers of individuals for cross pollination and to
ensure adequate seed set.
Based on current understanding of the species' life history,
sufficient rain in conjunction with wetter-than-average fall weather
appears to trigger germination events. Seedlings may be generally
present in suitable habitat throughout the dunes, especially during
above-normal precipitation years. In intervening drier years, plant
numbers decrease as individuals die and are not replaced by new
seedlings. The species likely depends on the production of seeds in the
wetter years, and the persistence of the seed banks from all years, to
persist until appropriate conditions for production and germination
occur. Further research and modeling are necessary to better understand
the dynamics of this system and how the species may be responding to
natural and man-made disturbances within its range. As one of the peer
reviewers noted, this species has a complex life history, and while it
can act as a perennial, it is more apt to behave as an annual (McCue,
2003).
The relative contribution of first-year plants of Peirson's milk-
vetch to the seed bank and survival of the taxon is not fully
understood. The available data suggest that older age classes may
produce substantially more seeds than first-year plants and that,
therefore, the older persisting plants may be more important for
reproductive success (Phillips and Kennedy 2002, Romspert and Burk
1979). Phillips and Kennedy (2002) reported that the older plants
produced a mean of 171 fruits per plant, compared to an estimated 5
fruits per each younger plant in the earlier spring survey. Romspert
and Burk (1979) state that Peirson's milk-vetch plants that become
reproductive the first season do not contribute a great deal to the
seed bank, but that mature plants produced copious amounts of seeds.
In desert plants, the majority of seedlings may die off at the
onset of the dryer season as noted by previous reports. Pavlik and
Barbour (1988) studied the establishment and survivorship pattern of
Astragalus lentiginosus var. micans, another dune endemic plant, and
recorded a complete crash of the 1984-1985 seedling cohort. These
authors also reported that 54 percent of the 1985-1986 cohort of
seedlings survived. However, none of these plants reached reproductive
maturity within the year. Thus, a large or very large number of
seedlings of Peirson's milk-vetch may succumb prior to producing and
dispersing seeds. Peirson's milk-vetch populations must then rely on
the cumulative seed bank, not the seed production of a single year even
if germination was high. This demonstrates the need for long-term
analysis of the population dynamics of this plant to adequately assess
adaptive management concerns and recovery actions.
Seed Biology
The fruits of Peirson's milk-vetch are 0.8 to 1.4 in (2 to 3.5 cm)
long, one chambered, hollow, and inflated.
[[Page 31525]]
Peirson's milk-vetch fruits contain 11 to 16 large, flattened black
seeds. The seeds, among the largest seeds of any Astragalus in North
America (Barneby 1964), average less than 0.1 ounces (oz) (15
milligrams (mg)) each in weight and are up to 0.2 in (4.7 millimeters
(mm)) in length (Bowers 1996). Seeds are either dispersed locally by
falling out of partly opened fruits on the parent plant, salt-shaker
style, or by their release from fruits blown across the sand after
falling from the parent plant. Seeds require no pre-germination
treatment to induce germination, but show increased germination success
when scarified (outer cover is broken). Porter (in litt. 2002a)
reported about 98 percent of scarified seeds germinated while only 21
percent of unscarified seeds germinated. In germination trials
conducted by Romspert and Burk (1979), 92 percent or more seeds
germinated within 29 days at temperatures of 77 [deg]F (25 [deg]C) or
less, and no seeds germinated at temperatures of 86 [deg]F (30 [deg]C)
or higher. This indicates that seeds on the dunes may likely germinate
in the cooler months of the year. Porter (in litt. 2002a) reported
that, under greenhouse conditions, seed germinated within 5 days of
sowing. In the same report, Porter identified the primary dormancy
mechanism in Peirson's milk-vetch is the impermeability of the seed
coat to water. He demonstrated little loss of viability in seeds stored
for three years, consistent with species having a seed bank (Given
1994). Dispersed seeds that do not germinate during the subsequent
growing season become part of the seed bank (Given 1994). Romspert and
Burk (1979) noted that older plants were the primary seed producers,
and plants that become reproductive in the first season do not make
significant contributions to the seedbank. Considering statements by
Phillips and Kennedy (2002) that plants in early 2001 were estimated to
produce 5 fruits per plant compared to 171 counted in a small sample of
older plants that year, it is likely that older plants are important
contributors to the seed bank and survival of Peirson's milk-vetch.
In a given year, an annual or short-lived species can fluctuate
between large numbers of plants to few or even no plants. Many species,
and Peirson's milk-vetch may be one of them, have periodic ``rescue''
episodes from the seed bank where large flushes appear when germination
conditions are suitable (Elzinga et al. 1998). To the extent that
plants are precluded from adding seeds to the seed bank by being
eliminated by summer drought, herbivory, and OHV impacts, these
individuals cannot be expected to contribute to the reproductive
success of Peirson's milk-vetch. Development of a seed bank and
associated dormancy allows plant species to grow, flower, and set seed
in years with most favorable conditions (Given 1994). When measuring
seed bank dynamics, to determine the viability and productivity of a
seed bank, it is considered necessary to estimate the rate of seed
mortality and aging, the amount of seed removed by predators, and the
variability in germination events are among the factors considered
necessary (Elzinga et al. 1998).
Distribution and Habitat
Astragalus magdalenae var. peirsonii is reported from northeastern
Baja California, Mexico (Barneby 1959, 1964; WESTEC 1977; Spellenberg
1993), and has been verified in the Gran Desierto of Sonora, Mexico
(Felger 2000). In the United States, this plant is restricted to about
53,000 acres (21,500 hectares) in a narrow band of the central portion
of the Algodones Dunes of eastern Imperial County, California, which
are one of the largest dune fields in North America. The Algodones
Dunes are often referred to as the Imperial Sand Dunes, a designation
derived from their inclusion in the Imperial Sand Dunes Recreation Area
(ISDRA) established by the Bureau of Land Management (BLM). Nearly all
lands in the Algodones Dunes are managed by the BLM. However, the State
of California and private parties own small inholdings in the dune
area. Approximately 52,780 ac (21,359 ha) of the 185,000 acre ISDRA
have been proposed as critical habitat for A. m. var. peirsonii (68 FR
46143).
The western boundary of the dunes is marked by a series of
parallel, longitudinal southeast trending ridges. The northern third of
the dunes is narrow, about 2 mi (3 km) wide, and increases in elevation
from 200 to 300 feet (ft) (60-91 meters (m)) in the northern portion to
300 to 400 ft (91 to 121 m) in the southern portion north of Highway
78. Areas in the central portion of the dunes reach an elevation 500 ft
(152 m) south of State Highway 78, but reach elevations of only 200 ft
(60 m) for most areas just north of Interstate 8. The central portion
of the dunes is wider, about 5 mi (8 km), and is characterized by deep
bowls (hollows among the dunes) and slip faces (areas so steep that the
loose sand naturally cascades downward) that run transverse to the
primary ridge line (Norris and Norris 1961). The area south of
Interstate 8 is generally characterized by a lower elevation, dunes
less than 300 ft (91 m).
The Algodones Dunes are one of the driest and hottest regions in
the United States. Romspert and Burk (1979) reported average
precipitation between 1941 and 1970 was 2.6 in (67.8 mm) per year.
Rainfall amounts differ from place to place and from year to year with
areas to the northwest being generally dryer than those to the
southeast (Willoughby 2001). Habitat for this plant is found in a band
that runs parallel to the active, linear dunes on the western edge of
the dune field in a northwest to southeast direction. The band is
between these active linear dunes on the west and transverse ridge
dunes to the east. This includes the area within the central dunes
between State Highway 78 and Interstate 8. The dunes in this band are
composed of a series of transitional crescentic ridges (Muhs et al.
1995). A. m. var. peirsonii occurs on the open, higher, more active
dune areas with generally less than 20 degrees slope, in a vegetation
community referred to as psammophytic (dune loving) scrub (Thorne 1982;
Willoughby 2000).
Psammophytic scrub in the dunes proper occurs on the relatively
stable substrates on the leeward side of the dune ridge tops in areas
gradually sloping up from the bowls at the bases of the steep leeward
slip faces (Phillips and Kennedy 2002). Because of the tiered nature of
the dune system, a system of alternating slopes and swales, areas
suitable for development of psammophytic scrub and thus Peirson's milk-
vetch occur as scattered occurrences distributed among the dunes. These
areas are protected from extreme deposition or removal of sand
(Phillips and Kennedy 2002) and may shift in position over time.
Therefore, the distribution and relative abundance of the plant varies
from place to place and over time (WESTEC 1977, Willoughby 2000, 2001;
Phillips and Kennedy 2003).
Abundance
Peirson's milk-vetch exhibits temporal variability in plant numbers
apparently associated with annual precipitation patterns. Based on
current understanding of the plant's life history, sufficient rain in
conjunction with cooler fall weather appears to trigger germination
events. Seedlings may be generally present in suitable habitat
throughout the dunes, especially during above-normal precipitation
years. In intervening drier years, plant numbers decrease as
individuals die and are not replaced by new seedlings. The species
likely depends on the production of
[[Page 31526]]
seeds in the wetter years and the persistence of the seed bank.
WESTEC (1977) was a study done under contract to BLM to determine,
among other things, the distribution and abundance of seven sensitive
plant taxa including the Peirson's milk-vetch. BLM surveyed 34 selected
west-east transects in 1998 that were a subset of those used by WESTEC
(Willoughby 2000). The document compares its findings to those of the
earlier WESTEC study and concludes that all six of the plants taxa
monitored in 1998 are at least as abundant and widespread in the entire
dune system as they were in the 1977 WESTEC study. However, the BLM
document cautions that the data are not directly comparable because the
rainfall amounts were different for the two years and different
methodologies were used in the two studies.
The number and location of standing plants may vary considerably
from year to year due to a number of factors including the amount,
timing, and location of rainfall; temperature; soil conditions; and the
extent and nature of the seed bank. BLM continued to monitor the
Peirson's milk-vetch population along the 34 transects and reported
that 942 plants were found in 1999 and only 86 plants in 2000, both low
rainfall years compared to the wetter year 1998, when 5,064 plants were
found (Willoughby 2001).
In spring 2001, Thomas Olsen and Associates (TOA) conducted a
survey of a portion of the Peirson's milk-vetch populations on
approximately 35,000 acres of the dunes that were open to vehicle
access. In the 13 days of ground surveys, approximately, 71,926 plants
were reported (TOA 2001), but this single census does not provide any
information on population trend. In addition, TOA (2001) states that
``extrapolation of the census data to the entire dunes or to other
specific areas was not warranted.'' Plant mortality over the short term
may also be considerable (Phillips and Kennedy 2002).
The count was reportedly the result of an explosive germination
event in response to wet conditions during the winter of 2000 through
2001 (TOA 2001). The record of steep decline of the cohort counted by
TOA in 2001 was tracked by Phillips and Kennedy (2002) who reported
that 26 percent of the plants seen in Spring of 2001 were present in
late 2001 and Phillips and Kennedy (2003) who reported that only 0.26
percent of the plants counted in Spring 2001 survived to Spring 2003.
In 2003, Phillips and Kennedy (2003) reported that many of the
germinants were already dead and that large numbers of those remaining
would likely die. This severe decline in the population in 2003 was
further documented by Porter (in litt. 2003a), reporting a similar mean
seedling survival of 0.19 percent in monitored plots for the 2003
cohort of Peirson's milk-vetch.
Only 5 of these 71,926 plants encountered were considered to be
more than one season old (TOA 2001). The observation that only 5 plants
of the 71,926 individuals were censussed more than 1 season old
suggests that the seedlings for this species suffered a high degree of
mortality, or that the age classes were misidentified during the
survey. In contrast, a study prepared for the ASA (Phillips and Kennedy
2002) estimated that 26 percent of the plants counted in the spring
2001 survey survived to the winter of 2001 through 2002. Phillips and
Kennedy (2002) also found that these persisting plants produced a mean
of 171 fruits per plant, compared to an estimated 5 fruits per each
younger plant in the earlier spring survey. Phillips and Kennedy (2002)
data suggested that older age classes may produce substantially more
seeds, and that longevity may be an important factor for reproductive
success.
Public and Peer Review Comments
On September 5, 2003, we published a Notice in the Federal Register
(68 FR 52782) that the petition received on October 25, 2001 to delist
the Peirson's milk-vetch presented substantial information to indicate
the petitioned action may be warranted. As part of this Notice, we
requested information on the status of Astragalus magdalenae var.
peirsonii. In response, we received comments and information from
several organizations. In addition, to ensure that our status review
and 12-month finding are based on the best available scientific and
commercial information available, we solicited peer review of the key
documents supporting the petition from three scientists with
demonstrated and significant expertise and backgrounds in studies of
genetic diversity, seed banks, plant systematics, population genetics,
Astragalus field studies, and/or dune plant research. Documents
referenced by the petitioner, sent to the peer reviewers, included
Willoughby (cited as BLM) (2000, 2001); Thomas Olsen Associates, Inc.
(TOA) (2001); and Phillips and Kennedy (2002, 2003). These documents
represent considerable effort to address complex ecological issues.
They provide some useful data relative to the life history and ecology
of A. m. var. peirsonii. However, survey methodology and measures used
in these studies often differed.
All of the peer reviewers provided comments on some or all of the
documents provided to them. These included two documents considered
supportive to the delisting petition although not provided with the
petition (Phillips and Kennedy 2002, 2003). The peer reviewers
identified weaknesses in the supporting documents or limitations of the
data that was used to support the delisting petition. In particular,
the peer reviewers discussed the limitations of each survey methodology
used in the various documents and cautioned the use of data
extrapolation. For example, a few of the peer reviewers cautioned
against comparing the WESTEC (1977) and Willoughby (2000) studies due
to the widely different survey methodologies. Several reviewers noted
that a few statements in TOA (2001) and Phillips and Kennedy (2002,
2003) were not completely supported by the data presented. The Service
has incorporated the data from these studies in this finding, however,
we have taken into account the specific data limitations discussed by
the peer reviewers. All of the comments and information provided by the
public and the peer reviewers were considered in the development of the
12-month finding and are cited in the finding, where appropriate.
Discussion of Listing Factors
When considering an action for listing, delisting, or reclassifying
a species, we are required to determine whether a species is endangered
or threatened based on one or more of the five listing factors
identified in section 4(a)(1) of the Act. These factors are: (A) The
present or threatened destruction, modification, or curtailment of its
habitat or range; (B) over-utilization for commercial, recreational,
scientific, or educational purposes; (C) disease or predation; (D) the
inadequacy of existing regulatory mechanisms; and (E) other natural or
manmade factors affecting the continued existence of the species.
Delisting a species must be supported by the best scientific and
commercial data available and only if such data substantiates that the
species is neither endangered nor threatened for one or more of the
following reasons: (1) The species is considered extinct; (2) the
species is considered to be recovered; and/or (3) the original data
available when the species was listed, or the interpretation of such
data, were in error (50 CFR 424.11).
[[Page 31527]]
A. The Present or Threatened Destruction, Modification, or Curtailment
of Its Habitat or Range
The final listing rule (63 FR 53596, October 6, 1998) identifies
OHVs as a serious threat to Astragalus magdalenae var. peirsonii,
citing the fragile nature of the plants. Numbers and distribution of
OHVs have increased since the species was listed (BLM 2003 and
references cited therein).
Impacts of OHV use on Astragalus magdalenae var. peirsonii plants
and habitat have been noted by most dune plant studies. For example,
``The occurrence of dune plants and heavy use areas for vehicles is, to
a large extent, mutually exclusive'' (TOA 2001). This supports similar
findings by Willoughby (2000, 2001), WESTEC (1977), Luckenbach and Bury
(1983), and ECOS, Inc. (1990). Because of the generally transient
nature of surface structure of the dunes, most quantitative measures of
OHV impacts are given in terms of numbers of plants impacted. The TOA
(2001) survey reported finding 667 OHV-impacted plants during 13 survey
days. Phillips and Kennedy (2003) reported finding 430 impacted plants
during 6 survey days. But in neither study were plants marked to
determine survival or reproductive success at a later date. Impacts to
A. m. var. peirsonii from OHVs continue to be noted (Phillips and
Kennedy 2003; Willoughby 2004) although no follow-up to measure long-
term impact or relative severity of impact has been done.
The impacts of OHV use on other types of desert vegetation have
been documented. Bury et al. (1977) compared eight paired sites in the
Mojave Desert in 1974 and 1975, examining the impact of OHV use on
creosote bush scrub and associated wildlife. There were fewer creosote
shrubs per hectare in plots with higher OHV use, and the proportion of
shrubs per plot damaged by OHVs increased with increased OHV use.
The North Algodones Dunes Wilderness (Wilderness) will continue to
be closed to OHV use. However, the Wilderness alone is not sufficient
to ensure the long-term survival of Astragalus magdalenae var.
peirsonii because this area provides only a small percentage of the
entire habitat for this species within the Algodones Dunes and the area
provides less available habitat for this plant relative to the areas
south of State Highway 78 that are open to OHV use.
The Bureau of Land Management estimates that only approximately 14-
16 percent of the habitat for Astragalus magdalenae var. peirsonii
occurs within the Wilderness. Between 75-80 percent of all known
colonies of Astragalus magdalenae var. peirsonii in 1977 were found in
the areas open to OHV activity; only approximately 20% of the larger
occurrences were found in the Wilderness (WESTEC 1977). Further, the
habitat within the Wilderness is not all suitable for this species.
Creosote bush scrub habitat, which does not support Astragalus
magdalenae var. peirsonii is more abundant in the Wilderness than in
the areas south of State Highway 78. The distribution of Astragalus
magdalenae var. peirsonii from 1998-2000 indicates a higher relative
abundance of plants in the central dunes south of State Highway 78 (BLM
2003). Thus, the Wilderness is not sufficient to sustain this species
because it does not provide sufficient habitat and habitat quality to
ensure the long-term survival of this species.
The recently released Recreation Area Management Plan (RAMP) (BLM
2003) proposes to reopen, to OHV use, all temporarily closed areas of
the dunes. Re-opening these areas will likely affect the Peirson's
milk-vetch found in these locations. While many of these areas were
likely inaccessible prior to the closure, the technological advances,
such as affordable global positioning system (GPS) units, cell phones,
and OHVs with greater range have enabled OHV use to penetrate further
into the dunes. This will likely affect more of the population than was
previously impacted.
Visitorship continues to increase in the ISDRA (BLM 2003) and has
outpaced previous estimations (BLM 1987). Since this plant was listed,
visitorship to the recreation area has continued to increase. Based on
the BLM (in litt. 2002), visitorship increased an additional 79 percent
between 1996 and 1999, and 111 percent over the base year of 1994. The
visitorship levels recorded in 1999-2000 (BLM in litt. 2002) were 149
percent higher than those projected for the year 2000 by BLM (1987).
The BLM (2002) estimated visitorship for 2002 to be 1,005,000. In fact,
according to BLM figures (Integrated Marketing Systems 2003), there
were over 1.4 million visitors. This is 400,000 visitors higher than
were projected. The BLM (2002) estimated range of visitorship projected
for 2012 is 1,418,000 to 2,071,000. User groups are advocating for
building as many camping pads as possible until ``Over a span of time,
100 percent of both sides of the road would be camping pads'' (ASA
2002). Shifts in visitation have also been reported by the BLM
(Schoeck, BLM in litt. 2001) indicating that, by the late 1990s and
early 2000s, day use of the central dunes between State Highway 78 and
Interstate 8 had become heavy and continues to increase. In the late
1970s visitation was concentrated primarily to major winter holiday
weekends, with Thanksgiving week receiving the highest numbers of
visitors. However, day use has been reported to be increasing on non-
holiday weekends as well (Schoeck, BLM in litt. 2001).
Significant impacts from OHV use on Astragalus magdalenae var.
peirsonii habitat have been observed at or near the OHV staging areas
(Willoughby 2000). The TOA (2001) report supports the BLM findings
(Willoughby 2000, 2001) regarding limited occurrence of dune plants
associated with heavy OHV activity: ``The occurrence of dune plants and
heavy use areas for vehicles is to a large extent mutually exclusive.''
This corroborates earlier findings by WESTEC (1977), Luckenbach and
Bury (1983), and ECOS, Inc. (1990), and was reported in the final
listing rule (63 FR 53596). The coincidence of timing of seedling
establishment and the cooler months (OHV season) are among the reasons
for the plants' susceptibility to impacts from OHVs (Romspert and Burk
1979). Luckenbach and Bury (1983), in non-replicated studies of paired
plots along Highway 78 in the Algodones Dunes, report reduced numbers
of herbaceous and perennial plants, arthropods, lizards, and mammals
between areas closed to entry (control plots) and those exposed to
heavy OHV use. Control plots had 2.4 times the number of species, 10
times the numbers of individuals within these species, 9.4 times the
vegetative cover, and 40 times the volume of shrubby perennials as
compared to the OHV-impacted areas (Luckenbach and Bury 1983). These
data are from localized plots and were not intended to be extrapolated
to the dune system as a whole but rather are presented here to
illustrate the effects of OHV use on biota. Willoughby (2001) presented
data, albeit limited, indicating a higher percentage of A. m. var.
peirsonii seedlings in the areas closed to OHV use compared to areas
open to OHV use.
A map of vehicle tracks (Willoughby 2000) along selected transects
of the Algodones Dunes on a single day in 1998 showed that considerable
areas of potential habitat have been impacted. We have no evidence that
the extent of vehicle tracks, as depicted on this map, will diminish in
the future. Nor do we know how the distribution and intensity of these
tracks changes over a growing season or recreation season. Astragalus
magdalenae var. peirsonii plants, if
[[Page 31528]]
present in those areas, may have been impacted; however, on-the-ground
counts coincident with the vehicle track mapped areas were not
performed. Because of the transient nature of sand dunes, impacts from
OHVs are usually reported in terms of plant numbers impacted or the
condition of the impacted plants. In their report, TOA (2001) found 667
plants impacted by OHVs over the course of 13 survey days. A seedling's
roots are especially sensitive to drying out if the plants or sand
surface are disturbed. There are potential direct impacts if OHVs run
over the delicate seedlings and indirect impacts, such as higher soil
and root desiccation, if sand disturbance occurs in close proximity to
the seedlings. Seedling death may result from both types of impacts.
Seedlings that sustain broken branches and live will produce fewer
flowers, fruits, and seeds that they otherwise would have produced.
Most recently, during their short survey period, Phillips and Kennedy
(2003) report that they found several hundred A. m. var. peirsonii
plants that had been impacted by OHVs. Neither TOA (2001) nor Phillips
and Kennedy (2003) described the degree, pattern, or frequency of
impacts to the habitat occupied by the plants, or to adjacent suitable
habitat used as access avenues to the impacted site. Follow-up surveys
to determine the effects of the impacts on the plant's survival and
reproductive output were also lacking. Willoughby (2004) did not record
the area associated with the OHV-impacted plants he recorded. The
early, and most sensitive, life history phases of Peirson's milk-vetch
plants occur between late October and late February. This period
directly overlaps five of the peaks of visitorship to the Algodones
Dunes that occur in the same time frame. These peaks in visitor use
include Thanksgiving (250,000), New Years (150,000), and Presidents Day
(100,000) as well as Halloween and Martin Luther King Day. Only two
other visitor peaks over 50,000 visitors occur during a typical
recreation year. The early elimination of a portion of a seedling
cohort means that there will be fewer plants to potentially survive to
become older plants. Older plants have been shown to produce many more
seed pods per plant than younger first year plants.
In a very limited study, Pavlik (1979) quantified the immediate
physical effects of direct contact with an OHV to four specimens of
each of three psammophytic plant taxa found on the Eureka Dunes in Inyo
County, California. One was Astragalus lentiginosus var. micans
(shining milk-vetch), a short-lived perennial to annual desert plant
similar to Astragalus magdalenae var. peirsonii. Damage to each of the
plants impacted was assessed in terms of percentage of shoots severed,
apices removed, flowers removed, foliage loss or damage, and damage to
underground parts of the plants. In this study, A. l. var. micans lost
50 to 90 percent of the shoots and stem apices with light to moderate
OHV activity.
Willoughby (2000) notes a similar abundance trend in both the
closed and open areas for OHV activity for five of the six monitored
plant taxa, including Peirson's milk-vetch. Willoughby (2000) states
that this is likely due to the fact that intensive OHV use did not
encroach on much of the plant's habitat over relatively large portions
of the open area (all of the dunes except the wilderness area at that
time). Willoughby (2000) further notes that this trend may be expected
to continue unless OHV use patterns change. Patterns of visitorship
have reportedly changed according to BLM with the advent of GPS units
and cell phones, which apparently embolden riders to use more remote
areas (Schoeck in litt. 2001). Also, the projected 82 percent increase
in visitorship by 2012-2013 over 1999-2000 levels (BLM 2002) will
likely result in intensification and dispersal of OHV impacts.
Willoughby (2000) also states that the BLM surveys are monitoring
programs and not research, and there are limitations to using the
information to assess the impacts of OHV use on the plants monitored.
This indicates the observational nature of the monitoring rather than
research that tests hypotheses related to measures of OHV impacts on
plants.
The early, and most sensitive, life history phases of Peirson's
milk-vetch plants occur between late October and late February. This
period directly overlaps five of the peaks of visitorship to the
Algodones Dunes that occur in the same time frame. These peaks in
visitor use include Thanksgiving (250,000), New Years (150,000), and
Presidents Day (100,000) as well as Halloween and Martin Luther King
Day. Only two other visitor peaks over 50,000 visitors occur during a
typical recreation year.
The period of plant sensitivity, approximately late October to late
February, includes seed germination as well as seedling emergence. A
seedling's roots are especially sensitive to drying out if the plants
or sand surface are disturbed. There are potential direct impacts if
OHVs run over the delicate seedlings and indirect impacts, such as
higher soil and root desiccation, if sand disturbance occurs in close
proximity to the seedlings. Seedling death may result from both types
of impacts. Broken seedlings will produce fewer branches which results
in fewer flowers and seeds than undamaged seedlings leading to a
gradual diminishment of the seed bank.
The early elimination of a portion of a seedling cohort means that
there will be fewer plants to potentially survive to become older
plants. Older plants have been shown to produce many more seed pods per
plant than younger first year plants. Surveys that found hundreds of
plants impacted in 2001 (TOA 2001) and 2003 (Phillips and Kennedy 2003)
were conducted between early March and mid May. The magnitude of impact
described in these reports is likely conservative, in that the surveys
occurred after the highest vehicular use.
One of the mechanisms of survival for this species is a seed-
setting strategy for producing large numbers of seeds per plant,
particularly by older plants. Additionally, as is the nature of seed
banks, not all of the seeds in the soil germinate the following year,
as a safety measure against population failure. Natural ecological
processes diminish the Peirson's milk-vetch seed bank. Natural factors
affecting the seed bank include seed viability, seed parasitism, seed
deposition in suitable habitat and at appropriate depth, age of the
seeds, and failure of an entire seedling generation due to range-wide
environmental conditions. Each of these factors can limit the number of
seeds available for germination. The timing of the germination of
seedlings, the most sensitive life-stage of PMV, also overlaps with the
onset and peak levels of OHV activity within the Algodones Dunes.
Several studies document plants that were run over by OHVs at the
Algodones Dunes and this activity likely results in the direct loss and
damage to seedlings. The likely mortality of seedlings and older plants
by OHV activity precludes their future contribution to the seed bank
further threatening the long-term recovery potential and viability of
this plant.
The available documentation attests to historical and ongoing,
heavy OHV impacts to Astragalus magdalenae var. peirsonii (WESTEC 1977;
ECOS, Inc. 1990; Willoughby 2000, 2001, 2004; TOA 2001, Phillips and
Kennedy 2003). Based on information noted above, visitorship is
expected to continue to increase (BLM 1987, 2002, 2003). and OHV use
will continue to pose a threat to the survival of A. m. var. peirsonii.
In summary, OHV use generally reduces the number of species and density
of
[[Page 31529]]
those species in a given area. The Pierson's milk-vetch seedling
establishment timing coincides with the heaviest use of OHV use, which
impacts seedlings reducing the number of older plants. The older plants
produce more seed, ultimately contributing the most seed to the seed
bank. Without establishment of the older plants the seed bank will
likely decrease. Given that this plant survives in a dry dune habitat
that is highly disturbed by its nature and experiences periods of long
periods of drought, increasing the size of the seed bank is key to the
long term survival and eventual recovery of the species.
B. Overutilization for Commercial, Recreational, Scientific, or
Educational Purposes
Current data do not indicate that these factors constitute a threat
to Astragalus magdalenae var. peirsonii at this time.
C. Disease or Predation
Herbivory was reported for some of the taxa of Astragalus in the
final listing rule (63 FR 53596). As part of a series of reports on the
natural history of Astragalus magdalenae var. peirsonii, Porter (in
litt, 2003a) noted the general poor health of adult plants and
attributed it to evidenced rodent and insect herbivory. Porter (in
litt. 2002a) reported ``nearly ubiquitous'' harvesting of leaflets and
young inflorescences by rodents in A .m. var. peirsonii populations.
Most of the plants had leaves, leaflets, and/or terminal portions of
the stems removed, likely by unidentified rodents that had left
abundant tracks around the milk-vetch plants. Porter (in litt. 2003a)
also found similar results in 2003. To the extent that rodents remove
photosynthetic tissue and young inflorescences, plants are likely to
exhibit a loss of vigor and reduction in reproductive output (i.e.,
seeds). Indeed, Phillips and Kennedy (2002) noted that seed bank counts
were lower in areas where they noted kangaroo rat (Dipodomys spp.)
tracks and dens and suggested that this should be investigated. Pavlik
(in litt. 2003) noted that rodents may be a constant, long-term source
of high seed mortality that could dramatically reduce the seed bank. As
yet unidentified weevils were observed to strip the epidermis from the
stems, which would affect the movement of food and water in the plants
(Porter in litt. 2003a).
Beetles, in the family Bruchidae, were reported to contribute to
the high mortality of seeds and reduced seed crop for Astragalus
magdalenae var. peirsonii by Romspert and Burk (1979). Larvae of these
beetles eat the contents of the seeds before emerging as adults. Fruits
collected in April continued to release beetles, into October (Romspert
and Burk 1979). Porter (in litt. 2003a) found between 45 and 86 percent
of the fruits on the few Astragalus magdalenae var. peirsonii plants,
where he could find fruits, were infested with bruchid beetles. The
range was 0 to 29 percent for dispersed fruits on the ground.
Similarly, for the obligate dune plant Astragalus lentiginosus var.
micans, Pavlik and Barbour (1985) found that dispersed fruits had about
66 percent of the seeds eaten or damaged by insect larvae compared to
86 percent of the seeds in fruits still on the plant. Also the number
of undamaged seeds decreased by more than 60 percent between April and
May, indicating that predation is highest at dispersal time. The
reduction of productivity of any given cohort of A. m. var. peirsonii
from seed predation is unknown but may locally be considerable in a
given year. Seed predation has been reported to cause significant loss
of ovules or seeds in Astragalus canadensis (Boe et al. 1989), and in
two other species of Astragalus (Green and Palmbald 1974).
Available information shows that rodent herbivory and seed
predation, as noted above, are not detrimental to the species by
themselves but, may be additive threats to Peirson's milk-vetch in the
presence of the other stressors that the population is currently
undergoing.
D. The Inadequacy of Existing Regulatory Mechanisms
The lack of regulatory protections for Astragalus magdalenae var.
peirsonii by the State of California cited in the final listing rule
(63 FR 53596) still hold true. Pursuant to the Native Plant Protection
Act (California Department of Fish and Game (CDFG) Code) and the
California Endangered Species Act (CESA), A. m. var. peirsonii was
listed as endangered in 1979. This plant is known to occur primarily on
BLM managed lands. BLM is not subject to the provisions of the CESA.
The BLM and the CDFG developed a habitat management plan in 1987 that
included provisions for monitoring transects every other year until
trends were established. However, little monitoring specific to
sensitive species was carried out by the BLM prior to the listing of A.
m. var. peirsonii. Since the listing, the BLM and the CDFG have been
conducting periodic monitoring for the rare plants on the Algodones
Dunes.
The BLM temporarily closed areas of the Algodones Dunes to OHV and
other traffic on November 3, 2000. However, the recent RAMP for the
ISDRA (BLM 2003) proposes to reopen those areas temporarily closed to
OHV activity. The opening of the temporarily closed areas will increase
the threat to Astragalus magdalenae var. peirsonii to some degree from
current levels. This would open all areas of the dunes to OHV use,
except for the Wilderness Area, which was the case when this species
was listed in 1998 (63 FR 53596). To help protect the plant, BLM has an
adaptive management and monitoring strategy in place. This will provide
corrective measures should existing management be found to cause
excessive, unacceptable impact to the plant. The majority of OHV users
are responsible recreationists on the dunes and avoid vegetated sites
(TOA 2001). However, there may be significant damage to populations of
A. m. var. peirsonii and its habitat, especially closer to the staging
areas. This would be the result of the focus of increased OHV activity
in a smaller area.
The designation of the North Algodones Dunes Wilderness was fully
considered and was one of the reasons for changing the listing status
from endangered, published in the proposed rule (57 FR 19844), to
threatened in the final rule (63 FR 53596). As stated in the final
listing rule (USFWS 1998), ``While this taxon remains vulnerable to the
OHV use occurring over most of its dune habitat, the Service believes
that the dispersed nature of its colonies and the wilderness
designation reduce the potential for immediate extinction.''
Available information does not indicate that adequate regulatory
mechanisms are in place to protect Peirson's milk vetch.
E. Other Natural or Manmade Factors Affecting Its Continued Existence
The vast majority of OHV users likely avoid Astragalus magdalenae
var. peirsonii and other biota on the dunes for safety and aesthetic
reasons. The impacts from OHVs can be incidental or purposeful.
Although the range-wide impact is difficult to assess, there has been
an increase in reports of vandalism to the habitat and individuals of
A. m. var. peirsonii. This was a specific concern expressed in the
critical habitat discussion of the final listing rule (63 FR 53596).
There has been no monitoring specifically for the distribution, extent,
and impact of vandalism to the plant across its range. Porter (in litt.
2002) describes both tracks and incursions of OHVs into areas outside
of the Wilderness Area that were closed to OHV traffic. Three of the 20
plants in one of Porter's monitored plots (Porter in litt. 2002) were
destroyed by vandals. There have
[[Page 31530]]
been other reported incidents of vandalism, some by our staff, and
others, but because of the time, lack of knowledge of intent, precision
of the description of the location, frequency of occurrence, and
percentage of the plant's range involved, it is difficult to assess the
cumulative impact to the species.
This species is also threatened by low numbers of reproducing
individuals, a circumstance that occurs from time to time. Movements
and fluctuations of populations have not been recorded long enough to
assess the full impact of significance to the survival of the taxon.
The BLM (Willoughby 2001) reported a total of only 86 plants throughout
its transect areas in the 2000 survey. TOA (2001) found only five
plants more than a year old in their survey of all of the areas open to
OHV use. This would be an extremely important fact requiring
explanation and assessment if only five plants of an herbaceous
perennial taxon had persisted from the previous season, especially in
light of seed production as mentioned before. The older, larger plants
contribute more to the seed bank than younger flowering juveniles
(Romspert and Burk 1979; Phillips and Kennedy 2002). Random events may
have a significant detrimental effect on the species when so few
individuals are present or when the habitat requirements are so narrow
that random environmental conditions can result in the demise of an
entire cohort. This was apparently the case with the loss of the entire
2003 cohort of seedlings (Phillips and Kennedy 2003; Porter in litt
2003). The ecological impact of any cyclic depletion and restoration of
the seed bank is unknown.
Astragalus magdalenae var. peirsonii, like some other narrow
endemic dune taxa, is subject to debilitating or lethal environmental
conditions, such as drought or excessive unseasonal winds, across its
entire range that can affect an entire cohort of plants. Pavlik and
Barbour (1988), noting the establishment/survivorship pattern of
Astragalus lentiginosus var. micans, another dune endemic plant,
reported a complete crash of the 1984 through 1985 seedling cohort.
Even though 54 percent of the 1985 through 1986 cohort of seedlings
survived, none of these plants reached reproductive maturity within the
year. This was apparently the case for the 2003 cohort of A. m. var.
peirsonii. Phillips and Kennedy (2003) noted that many of the
germinants were already dead and that large numbers of those remaining
would likely die. Porter (in litt. 2003a) reports a similar mean
seedling survival of 0.19 percent in monitored plots for the 2003
cohort of A. m. var. peirsonii. Environmental conditions unsuitable for
this plant can occur at irregular intervals or can persist for several
years. Low numbers combined with periodic, range-wide, debilitating
environmental conditions pose an ongoing potential threat to this
plant.
Finding
We have carefully assessed the best scientific and commercial
information regarding the biology of this species and its threats. We
reviewed the petition and associated documents, information available
in our files, other published and unpublished information submitted to
us during the public comment period following our 90-day petition
finding. We reviewed new data and information on the life history and
ecology of Peirson's milk-vetch; however, we did not find convincing
information that Peirson's milk-vetch was listed in error.
The North Algodones Dunes Wilderness (Wilderness) will continue to
be closed to OHV use. However, the Wilderness alone is not sufficient
to ensure the long-term survival of Astragalus magdalenae var.
peirsonii because this area provides only a small percentage of the
entire habitat for this species within the Algodones Dunes and the area
provides less available habitat for this plant relative to the areas
south of State Highway 78 that are open to OHV use.
The Bureau of Land Management estimates that only approximately 14-
16 percent of the habitat for Astragalus magdalenae var. peirsonii
occurs within the Wilderness. Between 75-80 percent of all known
colonies of Astragalus magdalenae var. peirsonii in 1977 were found in
the areas open to OHV activity; only approximately 20% of the larger
occurrences were found in the Wilderness (WESTEC 1977). Further, the
habitat within the Wilderness is not all suitable for this species.
Creosote bush scrub habitat, which does not support Astragalus
magdalenae var. peirsonii is more abundant in the Wilderness than in
the areas south of State Highway 78. The distribution of Astragalus
magdalenae var. peirsonii from 1998-2000 indicates a higher relative
abundance of plants in the central dunes south of State Highway 78 (BLM
2003). Thus, the Wilderness is not sufficient to sustain this species
because it does not provide sufficient habitat and habitat quality to
ensure the long-term survival of this species.
This species likely depends on the production of seeds in the
wetter years and the persistence of the seed bank from previous years
to survive until appropriate conditions for germination occur again.
However, assertions that the reproductive success of Peirson's milk-
vetch is not dependent on the longevity of individual plants but on
each plant's ability to produce and drop seeds in their first year is
not supported by the available documentation. First year plants produce
substantially less seeds than older plants (5 fruits per plant as
opposed to 171 fruits per plant) (Phillips and Kennedy 2002). TOA
(2001) reported plants produce seeds their first year, however those
age classes may have been misidentified. In addition, an entire cohort
of seedlings may die off in a given year without producing seeds
(Phillips and Kennedy 2003, Porter in litt. 2003). Therefore, the key
to survival and recovery is having a large seed bank. The available
information on the rate of seed deposition to the seed bank and the
longevity of seeds in the seed bank does not support claims of a
healthy seed bank. Given, the low numbers of Pierson's milk-vetch,
other natural predators (seed predatory beetles and kangaroo rats)
further threaten the species by depleting an already low seed bank
reserve. Peirson's milk-vetch also exhibits a wide variation in numbers
of standing individuals found in any given year. Plant count data
between years is often not directly comparable due to differences in
rainfall amounts and methodologies. Long-term studies need to be
undertaken to show the population trends for the species.
Documentation available attests to historical and ongoing OHV
impacts to Peirson's milk-vetch (WESTEC 1977, ECOS 1990, Willoughby
2000, 2001, 2004, TOA 2001, Phillips and Kennedy 2003). Areas within
the dunes subject to intensive OHV use have a lower abundance of
Peirson's milk-vetch (e.g., staging areas). Plants within the interior
portions of the dunes have remained less affected by OHV use, however,
the advent of GPS and increased vehicle fuel efficiency now enable OHV
users to travel further into the interior of the dunes without getting
disoriented and lost. Available information suggests OHV use will
continue to pose a threat to the survival of Peirson's milk-vetch.
Given the low numbers, other threats such as rodent and insect
herbivory, seed predation, and vandalism are contributing to the
cumulative threats to the Peirson's milk-vetch.
After a thorough review and consideration of all information
available, we find that delisting Peirson's milk-vetch is not warranted
at this time and that this species should remain classified as a
threatened species. In making this determination we have followed the
procedures set
[[Page 31531]]
forth in section 4(a)(1) of the Act and regulations implementing the
listing provisions of the Act (50 CFR part 424).
We will continue to monitor the status of the species, and to
accept additional information and comments from all concerned
governmental agencies, the scientific community, industry, or any other
interested party concerning this finding.
References Cited
A complete list of all references cited in this finding is
available on request from the Carlsbad Fish and Wildlife Office (see
ADDRESSES above).
Author
The primary author of this finding is the staff of the Carlsbad
Fish and Wildlife Office.
Authority: The authority for this action is the Endangered
Species Act of 1973, as amended (16 U.S.C. 1531 et seq.).
Dated: May 28, 2004.
Marshall Jones,
Acting Director, U.S. Fish and Wildlife Service.
[FR Doc. 04-12659 Filed 6-3-04; 8:45 am]
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