Simulating the potential effects of wildfire and forest management activities on Sierra Nevada fisher population size

Background/Question/Methods

The fisher (Martes pennanti) is a large member of the weasel family that depends on structurally complex forests with large, mature trees. In the southern Sierra Nevada mountains in California, fisher populations have dramatically declined. Remaining populations may be vulnerable to stand-replacing wildfires and fire management actions that could reduce or fragment critical habitat. We simulated wildfire and proposed fuels management activities on fisher habitat using a forest landscape change model, LANDIS-II. Simulated fire was a function of local weather conditions, topography, and spatially and temporally dynamic fuel types. Forest landscape model predictions of habitat change were subsequently used to estimate habitat quality in a general additive model (GAM). The results of the GAM were subsequently fed into a metapopulation model, PATCH, to estimate population size.

Results/Conclusions

Our results indicate that fisher population size is sensitive to the current fire regime and potentially very sensitive to any climate induced increase in fire sizes and intensities. In particular, there is a high potential for habitat fragmentation due to catastrophic fire events. Fisher habitat was found to be only modestly sensitive to management by itself and management could potentially reduce the risk of habitat loss due to wildfire and reduce the risk of severe population decline. However, to be consistently effect, fuels management would need to be more extensive and more intense than is currently practiced or allowed. These results are being used to inform decision-making to protect and enhance the quality of fisher habitat.