Carryover effects of forestry practices on wood frogs

Background/Question/Methods   Research has shown that metamorphosis is not a new beginning. Stressors in an individual's larval habitat affect their growth, development, and survival post-metamorphosis. However, it is unclear what the relative importance of larval and post-metamorphic stressors are to overall fitness. In order to address this question, we examined the effects of forestry practices on the performance of wood frogs in the aquatic and terrestrial stages using in situ cattle tanks and terrestrial enclosures. For the larval stage, we examined the two main factors changed by clear-cutting around ponds: shading and litter. We placed cattle tanks in clusters in clearcuts and forest and manipulated litter type (leaf litter, grass litter, or no litter) for a fully factorial design. We placed forty wood frog hatchlings in each tank and recaptured them at metamorphosis. Metamorphs were then placed into terrestrial enclosures in clearcuts and forest such that one (low density) or two (high density) metamorphs from each aquatic treatment combination was present in each enclosure. We determined survival and growth in September and May and used model ranking to determine whether aquatic and/or terrestrial treatments were better predictors of wood frog performance.

Results/Conclusions   We found that terrestrial treatments were the best predictors of juvenile wood frog survival to September, but the null model was the highest-ranking model for survival to May. Survival was lower in clearcuts with downed wood absent than clearcuts with downed wood present or forest treatments. The best model for juvenile body size included a combination of the aquatic and terrestrial treatments for both September and May However, there was much greater support for this model in September than May, possibly indicating that the effects of the aquatic environment begin to wane with greater time spent in the terrestrial environment. Juveniles were larger if they spent their larval period in clearcuts with leaves and were smaller from enclosures in clearcuts with downed wood absent. These results indicate that the terrestrial environment is most important for juvenile performance, but even in stressful environments, carryover effects from the larval stage can be detected. Our study demonstrates the importance of examining the effects of stressors on multiple life stages simultaneously. Landuse changes can affect the aquatic and terrestrial stages of amphibians in different ways, and understanding these effects is important for successful management.