Intermediate levels of soil disturbance maximize alpine plant diversity

Abstract

The intermediate-disturbance hypothesis^1–9 predicts that plant species diversity will be maximized at intermediate levels of vegetation disturbance (D). As yet, the only directly applicable data seem to be from Grime's¹ study, which served more as a source of the conjecture than an independent test of it, and in which disturbance was not measured. Here I report an analysis of the relationship between soil frost disturbance and diversity of vascular plant species in Arctic–alpine fellfield vegetation in the White Mountains of interior Alaska. To study plant species diversity, a measure (SD) is calculated, which is affected by both the number of species (species richness, SR) and the evenness of their relative abundances. I show that intermediate levels of disturbance maximize SD by influencing the evenness of relative abundances, but not the overall number of species. Because disturbances caused by soil frost action and animals are frequent in many Arctic and alpine tundras, these results imply that disturbance could be an important factor in species diversity differences within and between tundra vegetation types. If theoretical predictions^1–9 are confirmed by dynamic tests now under way, the theory could be applied to problems of tundra vegetation management such as revegetation and disturbance by trampling and vehicles.