Cumulative Effects of Contemporary Timber Harvest on Fish Abundance and Distribution 

Investigators: Robert E. Gresswell and Christian Torgersen, U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, Douglas S. Bateman and David Hockman-Wert, OSU College of Forestry, and Marc Novick, OSU Department of Fisheries and Wildlife.

Introduction

On public lands, restoration activities addressing the effects of land-use activities on aquatic habitats rely increasingly on ecosystem principles across large spatial scales. However, in western Oregon , public lands often occur in a matrix of private timberlands where harvest activities are subject to other regulations. These industrial forest systems have rarely been considered in the integrated management of forested landscapes. The goal of this research is to expand the understanding of physical and biological processes in streams subjected to contemporary forest harvest by studying a privately owned watershed in western Oregon . This study will initiate a long-term program examining fish and riparian invertebrates associated with temporally varying harvest activities. Changes in distribution and behavior of biota at different spatial scales, from local to basin-wide habitats, will be examined in the headwaters of Hinkle Creek on land owned by Roseburg Forest Products.

Interpreting effects of land-management activities on aquatic habitat, and ultimately on aquatic organisms, is hampered by the complexity of relationships among physical, chemical, and biological characteristics of terrestrial, riparian, and aquatic systems, especially at broader spatial scales. These complexities require integrated research across the landscape for extended periods. To date, most studies have been conducted at the site scale for a year or two, and protocols for examining these data in a broader context have not been well developed.

These research shortcomings are especially relevant to aquatic habitats on private timberlands. Industrial forestlands are the product of intensive management focused on continued production of wood resources through time. Much of the information concerning the effects of timber harvest in these areas is based on logging practices before 1990. The influence of current forest regulations is not adequately documented.

Small headwater stream channels can represent greater than 70% of the cumulative channel length in mountain watersheds. These small headwater channels are often directly affected by land-use activities, but the value of small channels and their associated riparian habitats has rarely been addressed by previous policies and management activities. Even where fish are not present, these headwater channels transport water, sediment, and wood that move from hillslopes to larger streams. Both ephemeral and permanent headwaters provide habitat for invertebrates that may be food for fish either locally or downstream. Quantifying the spatial and temporal extent of these processes will enhance the ability to anticipate potential downstream effects of harvest activities.

Critical questions concerning contemporary timber harvest practices on private industrial forests remain unanswered. Fundamental to answering these questions is determining how harvest activities in headwaters affect fish assemblages and behavior across the stream network. It is anticipated that changes in habitat, water quality, or food supply will affect fish in a dynamic way. The research proposes to address the following questions: 1) How do changes in physical and biological characteristics of tributaries without fish seasonally influence habitat quality in other portions of the stream network? 2) How do seasonal hydrologic changes in headwater streams affect fish abundance and distribution? 3) Does the abundance or diversity of fish fauna decline in response to changed habitat quality, or do organisms seasonally move to areas where habitat quality remains high?

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