Preliminary Study of the Effects of Headwater Riparian Reserves with Upslope Thinning on Stream Habitats and Amphibians in Western Oregon

Abstract

Abstract We conducted a preliminary examination of the responses of stream amphibians and instream habitat conditions to alternative riparian buffer zones with forest thinning upslope. Pre and posttreatment surveys were carried out on 68 headwater stream reaches (including 23 unthinned reference reaches) at 11 sites in western Oregon. Streams were in managed conifer stands, 40 to 80 years old, where the thinning treatment reduced stands from 600 trees per hectare (tph) to 200 tph. Treatments consisted of four widths of riparian buffers approximately 6, 15, 70, and 145 m on each side of streams. Over three study years, 3,131 individuals of 13 species were detected. For the more common instream and bank species analyzed, capture rates persisted posttreatment with no negative treatment effect from thinning with any of the buffer widths. More animals were detected after thinning in treatment reaches compared to reference reaches for rough-skinned newts (Taricha granulosa Skilton) occurring on stream banks, and for instream coastal giant salamanders (Dicamptodon tenebrosus Baird and Girard). Treatment effects on instream habitat parameters were not detected. Interannual variation was evident for western red-backed salamanders (Plethodon vehiculum Cooper), and several habitat conditions including pool-riffle ratio, stream spatial intermittency, stream width, and down wood. Overall, riparian buffers with moderate upslope thinning (200 tph) seemed to have retained the aquatic vertebrate community along channels among sites in the first 2 years posttreatment; however, several limitations of the study reduce the inference of the findings, and these preliminary results are best interpreted as hypotheses for further investigation.