Long-Term Exclusion of Folivorous Mammals in Two Arctic-Alpine Plant Communities: A Test of the Hypothesis of Exploitation Ecosystems

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Abstract
During 1987-1994 we monitored changes in vegetation in exclosures and permanent open plots established in two contrasting habitats: a productive 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 objective of the study was to test the following prediction of the hypothesis of exploitation ecosystems: exclusion of herbivorous vertebrates from the snow-bed initiates radical changes in the vegetation of the snow-bed, whereas in the tall herb meadow, the impact of grazer exclusion on the vegetation is modest. The vegetation within the snow-bed exclosures changed from a grassland to a herbfield during the experimental period. Transplanted tall herbs and seedlings of erect woody plants had high rates of survival and growth in snow-bed exclosures. No such changes were seen in the open snow-bed plots. Survival rates of transplanted woody plants and tall herbs in open snow-bed plots were low and the net growth rates of the survivors were close to zero. In the productive tall herb meadow, vegetational changes were modest on open plots and within exclosures. No clear treatment effects on survival or growth of transplanted woody plants and tall herbs were observed. The results of the experiment thus conformed to the predictions of the hypothesis of exploitation ecosystems.