The Relationship Between Measures of Annual Livestock Disturbance in Western Riparian Areas and Stream Conditions Important to Trout, Salmon, and Char

Abstract

Managing livestock disturbance in riparian zones in a manner that provides economic returns to ranchers while protecting streams is an important aspect of rangeland management on public lands in the western United States. Attempts to balance economic and ecologic outcomes have been made more difficult due to the presence of several salmonid species that are protected under the Endangered Species Act. One approach to proper management of livestock use near streams has been to define the allowable limits of disturbance using 2 metrics, streambank alteration and stubble height. We evaluated 153 stream reaches within the Interior Columbia Basin to determine if these 2 surrogates of livestock disturbance measured after the vegetative growing season were associated with stream conditions important to salmonids evaluated the following summer. We found that each stream habitat attribute that was evaluated (width-to-depth ratio, streambank angle, percent undercut banks, streambank stability, residual pool depth, percent pools, percent pool-tail fine sediments <2 mm, and wood frequency) trended toward lower-quality salmonid habitat as streambank alteration increased or as stubble height decreased. While the strength of these associations were variable, the slopes of the relationships suggest that managing the amount of streambank alteration or stubble height could influence stream conditions within the Interior Columbia Basin. Because improved stream conditions for salmonids corresponded to decreased livestock disturbance, the amount of disturbance allowed in a stream reach will need to reflect management expectations and the environmental setting within the allotment. As a starting point, we suggest the continued application of existing livestock disturbance standards in stream reaches with good habitat conditions, and the specification of more conservative disturbance standards in stream reaches that have degraded habitat conditions.