Vegetation and soil development at an upland taiga site, Alaska

Vegetation and soils on fluvial deposits of different ages were used to des cribe 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 yea rs are the dominant disturbance. Soil properties change little after afores tation due to disturbance from loess deposition and fire. Plant species abl e to resprout from roots following fires increase in importance with surfac e age. After about 4000 years, soils and vegetation reach a stable state wh ere frequently burning, aspen/white spruce/ericaceous shrub vegetation grow s on well-drained, poorly developed soils. We infer that this ecosystem per petuates itself through positive feedback involving clonal reproduction, ve getation's effects on the fire regime, and fire's effects on halting soil d evelopment and preventing the invasion of alternate plant communities. The brief fire-return interval and the abundance of clonal species indicate tha t secondary succession consists mainly of the immediate re-establishment of pre-fire dominants. The widely described scheme for post-fire succession i n the Alaskan taiga where deciduous trees are replaced over time by white s pruce does not occur here or at similar sites.