The Effects of Nearshore Forest Thinning on Upland Habitat Use by Pond-Breeding Amphibians in a Montane Coniferous Forest

Abstract

Forest thinning treatments are expanding in scope and scale to counter increasing wildfire risk. Such treatments are being applied in aquatic-adjacent forests that provide a critical habitat for sensitive amphibians, yet little is known about the impact of these treatments. We used a 5-year (2017–2021) before–after–control–impact experiment to investigate the effects of hand-thinning on pond-breeding amphibian activity around an ephemeral lake in the southern Cascade Range of California. We found that hand-thinning had no detectable negative effects on long-toed salamanders (Ambystoma macrodactylum) and western toads (Anaxyrus boreas) and significantly increased adult Sierran chorus frog (Pseudacris sierra) activity (χ2 = 4.70, df = 1, p = 0.030) in upland habitats. These results are consistent with pre-treatment habitat associations—chorus frog activity was higher when tree density was lower, and the treatment reduced tree density; adult long-toed salamanders and western toads were positively associated with canopy closure, which was not significantly reduced by the treatment. In addition, late-season surface activity of adult long-toed salamanders and chorus frogs was strongly associated with fall rain events when they tend to cluster very near the lake edge. Hand-thinning in aquatic-adjacent habitat may have minimal negative impacts, and even some positive impacts, on pond-breeding amphibians in coniferous forests, especially if treatments are not implemented during periods of high amphibian activity and do not substantially alter canopy closure.