Physiological costs of altered hydrothermal conditions in harvested forests

Abstract

Amphibians are among the most rapidly declining vertebrate groups worldwide, with habitat modification and climate change driving widespread population declines. Much work on amphibian vulnerability focuses on gradual shifts of climate change. While in many landscapes, habitat-altering disturbances such as clearcutting introduce sudden shifts in thermal and hydric environments on timescales far shorter than those of potential local adaptation and potentially removing critical microhabitat refugia. Such changes may be particularly relevant for amphibians, whose behaviour and ecological performance is linked to both body temperature and dehydration status. However, predicting the impacts of harvesting on amphibian hydrothermal physiology is not straightforward as higher temperatures (up to thermal optima) may increase performance, while dehydration will decrease it. To untangle these effects, I compared hydrothermal performance curves for Dryophytes versicolor with water loss rates and operative temperatures of replica frogs in harvested, edge, and unharvested boreal forest across four time-since-cut stages. Replica frog water loss was significantly correlated with real frog water loss (R2 = 0.86). I found performance declines past 15-20% dehydration and that baseline performance was lower at cooler temperatures and higher dehydrations. Clearcut environments reduced performance for gray treefrogs during overnight activity periods, particularly in uncovered microhabitats, across all time-since-cut groups, indicating that the increased hydrothermal vulnerability from harvesting is maintained through succession. By examining the relationship between performance, hydration, and temperature, we can begin to understand how removal or alteration of key microhabitats may impact individual fitness and population persistence within disturbed landscapes.