LONG-TERM DESTRUCTION OF SUB-ARCTIC WETLAND VEGETATION BY LESSER SNOWGEESE

During the last two decades, the mid-continent population of lesser sn ow geese (Anser caerulescens caerulescens), which breeds in the Canadi an eastern Arctic, has increased dramatically to at least 3 million bi rds. In spring, the birds follow the retreating snowline northwards to the breeding grounds. They forage intensively on shoots of sedges jus t south of the snowline, eating the swollen shoot bases and discarding the remainder. Exclosures were established in 1985/86 at La Perouse B ay, Manitoba to determine the effects of protection from foraging on t he shoot densities of sedges. Between 1986 and 1995, numbers of shoots increased from 1.1 to 2.2 times in exclosed plots, while numbers in g razed plots declined to between 0.19 and 0.33 times their original val ues. Sedge assemblages were replaced by moss carpets or standing water rich in peat debris. The ecological signficance of the results is dis cussed in relation to re-establishment of vegetation and the role of h erbivores in changing species assemblages.