THE GROWTH-RESPONSE OF GRAMINOID PLANTS TO GOOSE GRAZING IN A HIGH ARCTIC ENVIRONMENT

1 The response of plants to herbivory usually varies with the grazing regime experienced. We investigated (i) if the timing and frequency of grazing affected plant growth, (ii) if faeces deposition by herbivore s stimulated plant growth, and (iii) if grazing affected the total non structural carbohydrate (TNC) reserves in the below-ground vegetation of two arctic graminoids, Dupontia fisheri and Eriophorum scheuchzeri. 2 This study was conducted in polygon fens exposed to intense summer grazing by greater snow geese (Chen caerulescens atlantica) on Bylot I sland (73 degrees N) in the Canadian High Arctic. We manipulated the f requency (once or three times) and the timing (early, mid or late in t he season) of grazing and faeces deposition in controlled grazing tria ls using captive goslings. 3 Although ungrazed plants were taller than grazed ones at the end of the season, data on cumulative tiller elong ation (net above-ground height production) showed that plants grazed o nce or three times produced new foliage after each defoliation in both species. However, neither grazing (presence or absence) nor its frequ ency affected the net above-ground primary production (NAPP) or the nu mber of tillers at the end of the summer. Nitrogen concentration was h ighest in plants grazed three times, intermediate in those grazed once , and lowest in ungrazed plants. 4 Timing of grazing and presence of g oose faeces with or without grazing had no effect on plant growth. 5 E riophorum plants grazed three times had less TNC in their below-ground tissues than ungrazed plants, and the trend was similar in Dupontia. 6 Dupontia and Eriophorum were able to compensate for leaves lost to g razing and to maintain production at a level similar to ungrazed plant s, but at some cost (reduced below-ground reserves). The absence of an effect of faeces on plant growth may explain the absence of a positiv e effect of grazing on NAPP (i.e. overcompensation) in this ecosystem.