Six years of plant community development after clearcut harvesting in western Washington

Abstract

What roles do ruderals and residuals play in early forest succession and how does repeated disturbance affect them? We examined this question by monitoring plant cover and composition on a productive site for 6 years after clearcutting and planting Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco). The replicated experiment included three treatments: vegetation control with five annual herbicide applications superimposed over two levels of slash removal (bole only or total tree plus most other wood) and an untreated control. Three species groups were analyzed: native forest, native ruderals, and exotic ruderals. Without vegetation control, the understory was rapidly invaded by exotic ruderals but was codominated by native and exotic ruderals by year 6. Douglas-fir cover surpassed covers in the three species group covers at least 3 years sooner with herbicide treatments than without. Species richness and coverage were lower for all species groups with vegetation control than without vegetation control. The effects of organic matter removal were much less than that of vegetation control. As predicted by the Intermediate Disturbance Hypothesis, repeated vegetation control resulted in declining cover and richness; however, native forest species were surprisingly resilient, maintaining as much or more cover and richness as the ruderal groups.