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The Pacific fisher (Martes pennanti) is a rare forest carnivore strongly associated with dense, old forest with high canopy cover for denning and resting. The Sierra Nevada population is very small, genetically distinct, and isolated. Mixed-severity wildland fire is assumed to be a potentially greater threat than logging, and land managers are conducting large-scale forest thinning operations under the hypothesis that it is needed to reduce fire spread and severity. However, the relationship between fishers and fire has not been tested previously. I investigated this question with teams of dogs specially trained to detect the scat of Pacific fishers and, thus, their concentration of movements and habitat use. All scat samples were genetically verified. In surveys on the Kern Plateau in the southwestern Sierra Nevada, within unlogged post-fire forests with mixed-severity effects from large fires, and in unburned forests, I found that fishers selected Sierran mixed-conifer forests in both post-fire and unburned areas, and selected closed-canopied, mature/old forest in unburned forests, as well as burned forests that had this structure in the pre-fire condition. When fishers were near burned/unburned edges, they selected the within-fire side. Fishers used dense, mature/old forest that experienced moderate/high-severity fire at the same level as unburned dense, mature/old forest, and both males and females were found deep inside large fires—several km from the fire perimeter. These results indicate that fishers may benefit from the structural complexity of such post-fire habitat for foraging. This suggests mixed-severity wildland fire could be restored through managed wildland fire in these forests.

High tree mortality due to drought and insects often is assumed to increase fire severity once ignition occurs. In 2002-2003, coniferous forests in the San Bernardino Mountains, California experienced a significant tree mortality event due to drought and an outbreak of western pine beetles (Dendroctonus brevicomis). In October 2003, fire burned approximately 5,860 ha of conifer forest types in many beetle- and drought-affected stands where most pre-fire dead trees had retained needles. We used pre- and post-fire GIS data to examine how fire severity was affected by pre-fire tree mortality, vegetation characteristics, and topography. We found no evidence that pre-fire tree mortality influenced fire severity. These results indicate that widespread removal of dead trees may not effectively reduce higher-severity fire in southern California's conifer forests. We found that sample locations dominated by the largest size class of trees (>61 cm diameter at breast height (dbh)) burned at lower severities than locations dominated by trees 28-60 cm dbh. This result suggests that harvesting larger-sized trees for fire-severity reduction purposes is likely to be ineffective and possibly counter-productive.