Off-channel floodplain wetlands are biodiverse and provide critical wildlife habitat, yet they also face multiple stressors, predominantly non-native species, reduced river connectivity, and altered land use. Successful restoration and management of floodplain wetlands requires adequate understanding of how multiple stressors influence these species assemblages. As an initial step to develop that understanding, we conducted surveys for four native amphibians across 85 off-channel wetlands within the Chehalis River’s 100+ km-long floodplain, located in southwest Washington State. We then fitted multi-species Bayesian occupancy models to the monitoring data to examine how multiple stressors and habitat features influenced species occurrence.
Each species responded differently to stressors and habitat characteristics. Emergent vegetation consistently increased occupancy probabilities for all four native amphibians, perhaps because it can provide habitat refugia and/or promote high quality food resources. Non-native centrarchids reduced the probability of occupancy for two species (Rana aurora and Ambystoma gracile), whereas the presence of non-native American bullfrogs (Rana catesbeiana) did not influence occupancy probabilities for any of the native amphibians we studied. Sites with connectivity to flowing water also had higher occupancy probabilities for two species (Rana aurora and Ambystoma gracile). These preliminary results identify environmental conditions governing native amphibian occurrence in floodplain wetlands and will be used to inform management decision related to habitat restoration.