Over the past three decades the importance of downed wood for many wildlife species has been established, particularly for plethodontid salamanders. These salamanders are lungless and respire via nonpulmonary gas exchange through their skin, making the cool, moist microclimates found within decaying wood an important habitat component. Habitat suitability of downed wood as refugia is an increasing concern in managed forests of the US Pacific Northwest as downed wood decreases in both size and abundance. Additionally, reduced canopy cover occurring from timber harvest may result in temperature extremes within logs, rendering them unsuitable habitat. With the recruitment of large-diameter downed wood declining on managed landscapes, our objective was to determine whether smaller-diameter downed wood can provide thermal regimes similar to larger-diameter legacy downed wood. We examined temperature regimes within logs and soils to assess buffering capabilities against summer temperature extremes, which may be limiting to plethodontid salamanders. Temperature profiles of small- and large- diameter logs, as well as ambient soil and air temperatures were measured in a 60-year-old forest stand at two slope positions in three case studies representing different management strategies including riparian buffers and upland thinning.
Streamside and upslope maximum air temperatures experienced on all three streams were near or exceeded critical temperatures for western plethodontid salamanders. Air temperatures were generally more extreme in the upland compared to streamside, with the exception of the unthinned stand where differences between streamside and upslope areas were minimal. Very few differences were seen among large- and small-diameter logs, and soil, whose temperatures all remained below critical temperatures for plethodontid salamanders. However, large-diameter logs maintained a more constant thermal profile, whereas small-diameter logs and soils experienced greater diurnal temperature fluctuations. Our results suggest that logs of a wide size range, as well as soils, can provide sufficient protection against thermal extremes. However, further research is needed to better understand how reduced canopy cover affects temperature regimes of smaller- and larger-diameter downed wood and soils as suitable plethodontid salamander habitat relative to other functions, such as prey availability and moisture regimes.