Changing efficacy of fuel treatments for managing fire risk in a climate altered world

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Ashley Cale, Benjamin W. Sullivan, Jianning Ren and Erin Hanan, Natural Resources & Environmental Science, University of Nevada, Reno, Reno, NV

Background/Question/Methods
Climate change and historical fire suppression have altered fire regimes and increased wildfire risk in the California Sierra Nevada. To reduce fire risk, forest managers implement fuel reduction treatments. Fuel treatments are typically more effective in semiarid, fuel-limited forests where fire is constrained by fuel loading than in flammability-limited forests where fire is constrained by moisture.These two forest types are distributed within the Sierra Nevada, leading to adjacent different fire regimes. Under future climate scenarios, the effectiveness of fuel treatments for reducing fire risk will decrease in the most fuel-limited locations, which will likely become less productive with future drought, whereas fuel treatment effectiveness may increase in historically flammability limited landscapes. These responses will likely vary within watersheds due to differences in topography, soils, and vegetation. Here, we project how climate change will interact with fuel treatments to influence fire risk in a mixed conifer watershed which contains forests across the fuel- to flammability-limited continuum. We use a coupled ecohydrologic-fire regime model (RHESSys-WMFire) that simulates spatially explicit landscape processes and their interaction with fire spread within a watershed. We are conducting climate change (CMIP5 general circulation models), thinning (30 percent biomass removal), and counterfactual scenarios in a factorial design.
Results/Conclusions
Preliminary results focused on the historical records show that the effectiveness of thinning treatments for reducing fire risk vary across the watershed in response to underlying aridity gradients. In relatively flammability-limited forest stands, fire risk increases during drought conditions. These preliminary results support our hypotheses that forest thinning may become more effective in flammability-limited forests. This is counterintuitive because it indicates that fuels treatments should be implemented in forests that are currently mesic, but are likely to dry in the future. Such a change would require forest managers to change their fuels treatment strategies. However more work is needed to corroborate these findings under climate change scenarios. Future work will extend these findings from historical to future climate conditions and will also focus on the response of fuel-limited forests to test our hypothesis that fuel treatments will become less effective in the most arid sites under anthropogenic climate change. Our novel simulation modeling approach enables us to examine and identify key landscape and climatic drivers influencing fire regime shifts across the Sierra Nevada and provide ecologists and managers a tool for understanding current and future fire hazard.