Amphibian response to downed wood retention in managed forests: A prospectus for future biomass harvest in North America

Harvest of forest biomass, specifically downed woody material (DWM), will increase to meet rising demand for alternative energy sources. Biomass harvest may reduce habitat quality, abundance, and regional diversity of forest-dependent species such as amphibians. We synthesize available literature conducted in landscapes managed for timber production to (1) assess the current state of knowledge regarding DWM management and amphibian population dynamics and (2) identify pertinent research gaps for future biomass studies. In general, the 25 studies we reviewed reported that amphibian counts were positively correlated with DWM levels. Although studies involving terrestrial salamanders often stressed the importance of retaining DWM in harvested systems, empirical support for this conclusion is uncertain due to study- and species-specific variation in responses. Lack of a DWM effect was often attributed to downed wood that was not well decayed or was too small for amphibian use. We identified several critical research needs, including: (1) understanding temporal dynamics of DWM (e.g., recruitment and decay rates) in regenerating forests and its influence on amphibian populations, (2) determining how amphibian use of harvest units relates to configuration and characteristics of DWM, (3) understanding how DWM management influences amphibian demographic rates, and (4) development of sampling and analytical techniques that support separation of sampling error and ecological effects. We suggest that future studies estimate effects of biomass harvest and identify, test, and refine operational harvest strategies that minimize impacts to amphibian populations. We emphasize research should be conducted at scales relevant to management; specifically, stand and landscape scales.