Assessing alternatives for fuel reduction treatment and Pacific marten conservation in the southern Cascades and northern Sierra Nevada.

2018Forest managers are challenged to restore resilience to forests with an elevated risk of stand-replacing fire by using mechanical thinning and prescribed fire. Implementation of these methods can be constrained by mandates to conserve sensitive wildlife species like the Pacific marten (Martes caurina). Martens avoid simplified forest stands created by these fuel reduction treatments, and populations in the northern Sierra Nevada and southern Cascades are already fragmented. Implementing fuel reduction treatments may therefore threaten forest-dependent species like the Pacific marten by reducing available habitat and habitat connectivity.\ud A crucial question is whether reserving marten habitat from fuel treatment results in an elevated probability of large, intense wildfires compared to permitting treatment in these areas. I used a simulation framework to compare the potential for large fires when fuel treatments were implemented with and without marten habitat reserves, defined as areas where all treatment was prohibited. I also assessed wildfire risk to the dense, high elevation forests typical of marten habitat. I simulated fuel treatments in three watersheds (mean area: ~8,000 ha) and then used randomly-placed ignitions to measure each watershed’s capacity for fire spread. For each watershed, I varied the amount of area treated (10%, 20%, and 30% of the watershed) and the type of marten reserve (none; partial, where some marten habitat was reserved; and complete, where all marten habitat was reserved). I further expanded my simulations to a larger study area (~50,000 ha) to provide a complementary depiction of the relationship between habitat reserves and fuel treatment efficacy at the landscape scale.\ud Prohibiting fuel treatment within marten habitat had no significant effect on the ability of treatments to control the spread of fire. I observed an increase in the capacity for fire spread only in one instance, when the most restrictive reserve strategy reduced the total area eligible for treatment below the target 30%, the most ambitious treatment scenario. These results are optimistic for managers— effective fuels management was possible with simultaneous retention of large blocks of marten habitat. In contrast, wildlife risk to marten habitat increased when fuel reduction treatments were allowed only outside of predicted habitat areas. My simulations provide evidence that allowing some fuel treatment in the margins of predicted habitat could largely eliminate this increased risk, without incursion into core areas where martens are most likely to reside. Silvicultural prescriptions that can retain canopy cover and elements of old forest structure, while also increasing resilience to fire, would be preferable for reducing wildfire risk while mitigating the short-term effects of management action in these areas