Vegetation and soil development at an upland taiga site, Alaska

Abstract

Vegetation and soils on fluvial deposits of different ages were used to describe ecosystem development over millennia at a well-drained taiga site in the central Alaska Range. The youngest geomorphic surfaces are not forested, and lie in the active floodplain where they are disturbed by ice jams and flooding. Older surfaces are forested, and fires recurring every 40-60 years are the dominant disturbance. Soil properties change little after aforestation due to disturbance from loess deposition and fire. Plant species able to resprout from roots following fires increase in importance with surface age. After about 4000 years, soils and vegetation reach a stable state where frequently burning, aspen/white spruce/ericaceous shrub vegetation grows on well-drained, poorly developed soils. We infer that this ecosystem perpetuates itself through positive feedback involving clonal reproduction, vegetation’s effects on the fire regime, and fire’s effects on halting soil development and preventing the invasion of alternate plant communities. The brief fire-return interval and the abundance of clonal species indicate that secondary succession consists mainly of the immediate re-establishment of pre-fire dominants. The widely described scheme for post-fire succession in the Alaskan taiga where deciduous trees are replaced over time by white spruce does not occur here or at similar sites.