Vegetational development and the effect of geese on vegetation at La Pérouse Bay, Manitoba

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Abstract
The salt marshes at La Perouse Bay, Manitoba, are described. Unconsolidated, water-saturated sediment is colonized by Hippuris tetraphylla, Puccinellia phryganodes and Carex subspathacea. These sediments undergo frost heave, and on elevated mounds, Elymus arenarius var. mollis and Salix brachycarpa become established. This last species is the dominant one of the low willow tundra, which is the characteristic vegetation of the coastal strip. Where drainage is impeded in the upper marsh, relatively high salinities occur and species such as Salicornia europaea agg. and Triglochin maritima are present. A population of 10,000-20,000 lesser snow geese (Anser caerulescens) feed, in summer, on P. phryganodes, C. subspathacea, Potentilla egedii and E. arenarius var. mollis. The birds strip the shallow turf of Puccinellia in low-lying areas between clumps of willow. This terracing of the surface creates depressions which become filled with water and ice. The role of geese in producing these ponds in the upper levels of salt marshes in the Arctic does not appear to have been reported previously. The ponds are subsequently colonized by Carex aquatilis and T. maritima. The salt marsh gives way to an extensive fresh-water marsh dominated by species of Salix, Eriophorum angustifolium, Calamagrostis neglecta and Dupontia fisheri. The results are compared with data from other salt marshes in Hudson Bay and in the Arctic.