Downed Wood Microclimates and Their Potential Impact on Plethodontid Salamander Habitat in the Oregon Coast Range

Downed wood provides important faunal microhabitat in forests for numerous invertebrate taxa, small mammals and amphibians. Habitat suitability of downed wood as refugia is an increasing concern in managed Pacific Northwest forests, where overstory reduction may result in both reduced downed wood recruitment and increased temperatures within logs. We examined temperature profiles in western Oregon to assess differences in thermal regimes of logs and soil relative to Summer air temperature extremes and their implications with respect to habitat suitability for plethodontid salamanders. Temperature profiles of small- (0.3-0.45 m) and large- (0.7-1.0 m) diameter logs, as well as ambient soil and air temperatures, were measured in a 60-year-old forest stand at two different positions (0-5 m and 35-40 m from stream edge) in three case studies: 1) along a headwater stream with a narrow riparian buffer (similar to 6 m) and moderate upslope thinning; 2) along a headwater stream with a wider riparian buffer (similar to 15 m) and moderate upslope thinning; and 3) along a headwater stream with an unthinned upslope. Streamside and upslope maximum air temperatures measured during July 2006 along all three streams were near or exceeded 30 degrees C, the critical thermal tolerance threshold for western plethodontid salamanders. Streamside and upslope temperatures inside small logs, large logs and soils stayed below critical temperatures. Our results suggest that logs of a wide size range, as well as soils, may provide sufficient protection against thermal extremes in uncut forests and thinned stands with limited overstory.