The influence of forest structure on riparian litterfall in a Pacific Coastal rain forest

Abstract

Vegetative litter produced from riparian forests associated with alluvial rivers mediates nutrient and carbon cycling and indirectly shapes successional pathways and overall plant community characteristics. We quantified litter inputs at sites along the Queets River, a temperate rain forest river, in Olympic National Park, Washington. Study plots represented a chronosequence from pioneering vegetative patches on recently formed gravel bars to mature riparian forest terraces up to 350 years old. We observed an initial ~100 year linear increase in litter production (0.8–10.2 Mg·ha–1·year–1). Subsequently, we observed a shift to conifer dominance and development of a forest canopy with considerable structural complexity. During this time, litter production declined to ~5 Mg·ha–1·year–1. Empirical models of temporal changes in litter production suggest that the basal area and canopy volume of individual tree species are significant predictors (r2 = 0.60–0.99) of leaf and needle litter derived from that species, and can be used to predict litter production. We conclude that annual litter production is strongly influenced by structural forest characteristics and that litterfall rates can be estimated for a ~350 year chronosequence from stem basal area and canopy volume.