A Review and Meta-Analysis of the Effects of Riparian Zone Logging on Stream Ecosystems in the Pacific Northwest

Executive Summary

This report summarizes the results of nearly half a century of research on the effects of riparian zone logging on stream ecosystems in the Pacific Northwest of North America. After outlining the contemporary consensus on aquatic ecosystem management, I provide brief summaries of: (1) the effects of riparian logging on different physical and biological components of stream ecosystems, and (2) the functional relationship between riparian forest width (i.e. buffer width) and physical components of stream ecosystems. I then present a meta-analysis of thirty-four studies that have directly measured the effects of riparian logging on one or more of four physical and three biological components of stream ecosystems: water temperature, fine sediment load, large woody debris (LWD) load, habitat complexity, primary productivity, macroinvertebrate abundance/production, and fish abundance/production. Together, the summaries and meta-analysis suggest two conclusions. First, we have developed an empirically based and conceptually sound model for predicting the response of stream ecosystems to riparian zone logging. Second, there is substantial variation in the response of different physical and biological components of stream ecosystems to riparian zone logging. Departures from the general model are likely due to variation in channel geomorpholgy, and natural disturbance histories at both the stream and watershed scale. I suggest that the data support two key insights of the contemporary consensus on aquatic ecosystem management. First, because of their physical and biological connectivity, stream ecosystems should be managed at the watershed scale. Second, there is no single “ecological endpoint” for which individual streams can or should be managed. Accordingly, riparian zone management strategies, and associated monitoring efforts, should be implemented at the watershed scale. Ecologically sustainable riparian zone management will require protecting watershed integrity by ensuring that water, sediment, and organic debris continue to be introduced and transported through channel networks at spatial scales and temporal rates similar to those observed in unmanaged watersheds.