Inference of timber harvest effects on survival of stream amphibians is complicated by movement

Abstract/Summary

The effects of contemporary logging practices on headwater stream amphibians have received considerable study but with conflicting or ambiguous results. We posit that focusing inference on specific life stages may help refine understanding, as aquatic and terrestrial impacts may differ considerably. Within a before-after timber harvest experiment, we used recaptures of individually-marked amphibians and a joint probability model of survival, movement, and capture probability, to measure relationships with stream reach, stream gradient, pre- and post-harvest periods, and the timber harvest intensity. Downstream biased movement occurred in both species but was greater for Coastal Tailed Frog (Ascaphus truei) larvae than aquatic Coastal Giant Salamanders Dicamptodon tenebrosus.. For D. tenebrosus, downstream biased movement occurred early in life, soon after an individual?s first summer. Increasing timber harvest intensity reduced downstream movement bias and reduced survival D. tenebrosus but neither of these effects were detected for A. truei larvae. The limited distribution of A. truei among study reaches diminished our ability to measure treatment effects compared to D. tenebrosus.