LONG-TERM EXCLUSION OF FOLIVOROUS MAMMALS IN 2 ARCTIC-ALPINE PLANT-COMMUNITIES - A TEST OF THE HYPOTHESIS OF EXPLOITATION ECOSYSTEMS

During 1987-1994 we monitored changes in vegetation in exclosures and permanent open plots established in two contrasting habitats: a produc tive hemiarctic tall herb meadow and a less productive alpine snow-bed . In addition, we studied the survival and growth of transplanted tall herbs, woody plants and arctic-alpine plants together with their seed germination and seedling survival in the same habitats. The primary o bjective of the study was to test the following prediction of the hypo thesis of exploitation ecosystems: exclusion of herbivorous vertebrate s from the snow-bed initiates radical changes in the vegetation of the snow-bed, whereas in the tall herb meadow, the impact of grazer exclu sion on the vegetation is modest. The vegetation within the snow-bed e xclosures changed from a grassland to a herbfield during the experimen tal period. Transplanted tall herbs and seedlings of erect woody plant s had high rates of survival and growth in snow-bed exclosures. No suc h changes were seen in the open snow-bed plots. Survival rates of tran splanted woody plants and tall herbs in open snow-bed plots were low a nd the net growth rates of the survivors were close to zero. In the pr oductive tall herb meadow, vegetational changes were modest on open pl ots and within exclosures. No clear treatment effects on survival or g rowth of transplanted woody plants and tall herbs were observed. The r esults of the experiment thus conformed to the predictions of the hypo thesis of exploitation ecosystems.