Effects of Riparian Timber Harvest on Southeast Alaska Stream Habitat after 30–40 Years: Insights for Management

Abstract

AbstractLogging regulations in the Pacific Northwest and Alaska have evolved over time to alleviate the negative effects that historic harvest practices have had on stream habitat. While natural landscape factors largely control stream habitat, timber harvest can alter these influences, underscoring the importance of clarifying the effects of both for understanding and managing habitat in streams. We sampled areas in Southeast Alaska that had riparian zones harvested between 1980 and 1990, a period of less‐restrictive timber harvest regulations. Relationships between geomorphic and riparian factors with stream habitat informed a comparison of habitat under differing timber management strategies 30–40 years after harvest. Pool, substrate, and large wood characteristics were related to stream size, channel gradient, and channel confinement, whereas wood‐formed pools and large wood density were related to riparian factors. Pool characteristics in streams with harvested riparian zones were similar to those in streams with unharvested riparian zones. Large wood size distributions in streams with harvested riparian zones were also similar to those in streams with unharvested riparian zones and streams within forests managed for timber under contemporary regulations. These findings are likely due to legacy wood loads remaining and functioning to create habitat 30–40 years after harvest. Substrate size was related to timber management practices; streams with harvested riparian zones had smaller median particle sizes than unharvested streams. Wood loads remain and function instream decades after harvest, but the reduced supply of large‐sized wood from young‐growth riparian stands can result in declining habitat quality, especially in unconfined channels. Management strategies to enhance recovery of riparian stands with trees large enough to supply large‐sized wood are recommended. Our approach proved useful in teasing out legacy effects of past timber harvest from the effects of natural drivers on stream habitat, and the results can be used to help prioritize efforts aimed at conserving or restoring stream and riparian habitats in the region.