The Effects of Light and Moisture on Two Species from Contiguous Communities of South-Facing Bluffs in Interior Alaska, U.S.A.

Abstract

Steep, south-facing bluffs in interior Alaska support both deciduous forest and steppe vegetation. Most species show a range in community fidelity; however, others are restricted in their distribution. A steppe endemic (Potentilla hookeriana) and a forest species (Pyrola secunda) were grown in a greenhouse factorial experiment to test the hypothesis that light and soil moisture are important controls over plant performance and distribution on south-facing bluffs. Survival of both species showed strong and opposite light effects. Under low light, Potentilla survival was 48% less than under high light levels. Pyrola survival was reduced 44% in high light. Pyrola survivors showed few significant growth responses to either factor. These results suggest that the distribution and abundance of these species may be primarily a result of the effects of light on survival. The steppe species showed a greater range in growth response than the forest species, which is consistent with the fact that Potentilla occupies a broader segment of the forest-steppe gradient than Pyrola.