|ARCTIC ECOSYSTEMS IN PERIL: REPORT OF THE ARCTIC GOOSE HABITAT WORKING
POTENTIAL FOR RECOVERY OF DAMAGED HABITATS IN THE HUDSON BAY REGION
As long as the mid-continent population of lesser snow geese is
expanding at the conservative estimate of 5% per annum, there is little
likelihood that habitat recovery will be possible. As mentioned above,
direct and indirect effects of grubbing are cumulative. Even though full
restoration trials have not been undertaken, exclosure experiments of
unassisted re-vegetation in the absence of geese have indicated that at
badly damaged sites where the soil is hypersaline, it takes at least 15
years for swards to begin to develop. This length of time is beyond the
life expectancy of a single age cohort of lesser snow geese; after 8
years, 95% or more of a given cohort are dead (Cooke et al. 1995).
Hence, the effects on habitat outlive the geese. In intact but damaged
swards, exclosure experiments indicate that recovery in the absence of
geese can be rapid (Hudson Bay Project, unpublished data). However,
without eliminating geese from the site, any recovery is transitory.
Although restoration may be possible on an experimental basis, it is
unlikely that such assisted re-vegetation of damaged sites designed to
accelerate the rate of sward development will be practical; the continued
presence of geese, the costs and logistic difficulties, and other
priorities preclude full restoration schemes.
Given that unassisted, natural re-vegetation processes are the only
means by which these damaged areas can be recovered, the potential for
recovery among the various plant assemblages is examined below. This
discussion and the views expressed are tentative, as re-vegetation trials
are still in progress.
Coastal salt-marsh plant communities
Puccinellia phryganodes, the prime forage grass of lesser snow
geese, is a sterile triploid which has never been known to set seed
(Jefferies and Gottlieb 1982). Although it is widespread in salt marshes
throughout polar regions, it establishes at sites by clonal propagation.
Individual leaves, shoots and tillers have the ability to root in soft
sediment (Chou et al. 1992). Although Carex subspathacea sets seed, it is an irregular event, and many plants flower but fail to
set seed. Plants spread by clonal growth, and leaves, shoots and tillers
also root in soft sediment (Chou et al. 1992). Hence, the two main
forage species of lesser snow geese in the Hudson Bay region depend
heavily on clonal propagation for establishment and growth. Most of the
dicotyledonous plants appear to establish from a small, but persistent
seed bank in sediments (Chou, unpublished data).
Patches of the Puccinellia-Carex sward that are lightly grubbed
are capable of recovering within the season when exclosures are erected to
exclude geese. New shoot systems develop by stoloniferous or rhizomatous
growth and by the end of the first growing season, graminoid plant cover
is uniform across exclosed plots (Jefferies and Abraham, unpublished
data). Where exclosures are maintained for five growing seasons
substantial changes in plant assemblages occur (Bazely and Jefferies
1986). The grasses, Festuca rubra and Calamagrostis
deschampsioides, increase in abundance at the expense of the prostrate
graminoid species, Puccinellia phryganodes (Fig.
2.19). In addition, dicotyledonous species increase in abundance.
Plots when initially exclosed had 7 species present, five years later the
number of species had increased to 18, most of which were dicotyledonous
All indications are that if swards are only lightly grubbed so that
shoots remain in grubbed patches, rapid recovery is possible as long as no
further grubbing occurs. In the absence of grazing, changes in plant
assemblages are particularly rapid, indicating that natural regeneration
processes respond quickly to change.
Sand dune and beach ridge plant communities
No exclosures have been established where sand and gravels are now
devoid of vegetation, but where plants were present formerly. Heagy and
Cooke (1979) established a single exclosure on an old sand dune dominated
by Elymus arenarius in the vicinity of a nesting area used by
lesser snow geese. Prior to the establishment of the exclosure, breeding
geese pulled out shoots of this grass on the old dune, but individual
plants survived. After the exclosure was established growth of Elymus was considerable and the entire stand was dominated by the grass. We
anticipate that these communities can re-establish, but as in the case of
the salt-marsh, the time interval is likely to be long (> 10 years),
even in the absence of goose grazing.
Coastal meadow grassland and willow communities
Although there have been no formal re-vegetation trials in these
communities, exclosures were established by R. Harmsen in about 1985. They
were placed at different locations in these communities at sites where
grazing was heavy, but where no grubbing had occurred. The exclosures are
still in place, but monitoring of the vegetation has not taken place on an
annual basis. Although, the amount of above- ground biomass has increased
inside the exclosures, there is no evidence of significant changes in
species assemblages over the 10 year period. Individual species may have
increased in abundance, such as Triglochin maritima (heavily
grazed by Canada geese), but the exclosures are still dominated by Festuca
rubra and Calamagrostis deschampsioides and Salix
At sites which have been grubbed, so that gravels and marine clays are
exposed, no natural revegetation has occurred during the last 10 years.
The upper layers of sediment dry out in summer and are hypersaline.
Erosion of sediments has resulted in increased exposure of glacial
gravels. Exclosures established in these areas have remained unvegetated
for over a decade. In one exclosure wind-blown plant litter has collected
in one corner of a plot and provided a mulch above the hypersaline soil on
which plants have established. In effect, it is an artifact of the method
in that the chicken-wire exclosure traps plant litter.
Freshwater Wetland Vegetation
In 1995, a series of fully replicated exclosures were placed in sedge
meadows on the Cape Churchill peninsula, both where moss carpets or bare
peat were present and where there was little evidence of damage to
vegetation. Changes in the vegetation will be monitored, but it is too
early to indicate likely changes in plant assemblages.
Field observations made over a number of years indicate that two
herbaceous species, Potentilla palustris and Petasites
sagittatus invade the moss carpets and form a mat or stand of
vegetation. Additionally, prostrate willow species (Salix arctophila,
S. reticulata) grow by clonal propagation across the surface of the
moss. None of these species is eaten by the geese and this plant
assemblage is common where sedges have disappeared.
As mentioned earlier, peat barrens are widespread in some areas of the
Hudson Bay lowlands. Re-vegetation of this system depends very much on the
prevailing water regime. The hydrology precludes moss development,
although in wet years when the surface of the peat is moist, grasses such
as Dupontia fisheri establish, together with liverworts on the
bare surface. In dry years, or where sites are well drained, the surface
dries out and either chemical or physical processes lead to erosion of
peat and ultimately to exposure of clays and gravels. If this occurs,
there is little possibility of reestablishment of the original vegetation.
Where pools have developed in place of stands of Carex aquatilis and related species the mobility of peat debris appears to preclude
successful plant establishment. Around the edges of the more shallow ponds
(c. 20 cm of water) moss carpets have invaded the ponds, so that some
former ponds are now covered with a blanket of mosses.
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