EFFECT OF GRAZING BY GREATER SNOW GEESE ON THE PRODUCTION OF GRAMINOIDS AT AN ARCTIC SITE (BYLOT ISLAND, NWT, CANADA)

1 Arctic ecosystems are sensitive to grazing because of their low over all net primary production. We therefore studied the effect of greater snow geese on the production of arctic graminoids. 2 At Bylot Island, NWT (73 degrees N), breeding snow geese graze Eriophorum scheuchzeri and Dupontia fisheri in lowland polygon fens. Vegetation in seasonal e xclosures was sampled at 2-week intervals from mid-June to mid-August 1990, 1991 and 1993 (ungrazed areas) and compared with plant growth in short-term exclosures set up over grazed areas. Standing crop (above- ground biomass), net above-ground primary production (NAPP) and nitrog en content were determined for both plant species. 3 Goose faeces were used as an index of grazing intensity, Cumulative faeces counts incre ased from 2.2 faeces m(-2) in 1990-9.9 faeces m(-2) in 1993. 4 Peak ab ove-ground dry biomass of ungrazed areas averaged 33 g m(-2). In all y ears, goose grazing significantly reduced the above-ground biomass of Eriophorum and Dupontia. Over the 3 years, we estimated that geese con sumed from 65 to 113% of the cumulative NAPP of Eriophorum, and from 3 0 to 78% of the cumulative NAPP of Dupontia. Consumption of Dupontia, but not Eriophorum, was related to grazing intensity. 5 Cumulative NAP P of grazed areas was slightly lower than that of ungrazed areas at th e end of the summer. On an individual plant basis, cumulative NAPP of Dupontia, but not of Eriophorum, was reduced by grazing. Nitrogen cont ent of plants after grazing was higher than in ungrazed plants. 6 Alth ough grazed plants were able to grow new foliage, goose grazing did no t enhance NAPP at Bylot Island as has been reported elsewhere. This co uld be either because grazing occurs too late in the season when the r egrowth capacity of plants is low or because nutrients released from g oose faeces are absorbed by mosses and are not immediately available t o graminoids.