PLANT STRATEGIES ALONG MOUNTAIN VEGETATION GRADIENTS - A TEST OF 2 THEORIES

We test the predictions of two theories on plant strategies along vegetation gradients of a North Scandinavian mountain area, from herb-rich birch forests at 250 m. a.s.l. to the summit at 1530 m. a.s.l. According to Grime's theory. stressful physical conditions select for an adaptational syndrome called S-strategy. The theory predicts that the prevalence of S-strategic features increases monotonically from forests to hi-h-alpine boulder fields. Alternatively, the traits that Grime regards as S-strategic can be interpreted as adaptations to high natural-grazing pressure which culminates in moderately stressful habitats: productive enough to sustain grazers but yet so barren that moderate grazer densities suffice to deplete the vegetation. The observed vegetation patterns support this alternative view. We thus suggest that Grime's triangle should be revised as to make the role of grazing as the central causal factor behind the third strategy explicit.