POTENTIAL FOR RECOVERY OF DAMAGED HABITATS IN THE HUDSON BAY REGION

General comments

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damaged swards, exclosure experiments indicate that recovery in the absence of geese can be rapid (Hudson Bay Project, unpublished data).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 plants.

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 brachycarpa.

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.

Return to Table of Contents