1.problem statementthe lifespan of fuel treatments is constrained by vegetation recruitment and growth and resultant fuel accumulation (stephens ET AL. 2012), but IT also is affected by those…

1.problem statementthe lifespan of fuel treatments is constrained by vegetation recruitment and growth and resultant fuel accumulation (stephens ET AL. 2012), but IT also is affected by those treatments modulating susceptibility to non-fire disturbances. As climate change continues, forests are increasingly affected by multiple types of disturbances over short periods (e.g., decadal). Notably, outbreaks of bark beetles have been widespread and affect fire regimes in complex ways (kulakowski veblen 2015, fettig ET AL. 2022A). While much research has examined how susceptibility to outbreaks depends, in part, on the same attributes that are manipulated by fuel treatments (fettig ET AL. 2010), less attention has been placed on how those outbreaks, in turn, affect the long-term efficacy of fuel treatments. Conversely, fire severity (which is modulated by fuel treatments) also affects susceptibility to outbreaks (kulakowski veblen 2015, fettig ET AL. 2022B). Importantly, full accounting of the interactions among fuel treatments, outbreaks, and fires under an altered climate is lacking, setting the stage for unpredicted outcomes.2.objectiveswe propose four objectives for the montane forests of the sierra nevada mountain range (snmr), CA. (1) understand effects of fuel treatment and climate on fire severity. (2) understand how post-treatment fires and bark beetle outbreaks interact to determine longevity of fuel treatments. (3) understand how fuel treatments, fires, and bark beetle outbreaks interact to determine cumulative tree mortality, regeneration, and vegetation conditions. (4) model interactions among fuel treatments, fires, and bark beetle outbreaks under climate change scenarios. We hypothesize: (1) fuel treatments become less effective at reducing fire severity and their longevity decreases as drought becomes more extreme. (2) fuel treatments (alone or combined with subsequent fires) decrease occurrence and severity of outbreaks but not under extreme drought conditions. (3-1) cumulative tree mortality will be lower in stands with fuel treatments, but this effect will diminish with time since treatment and with more extreme drought. (3-2) high cumulative tree mortality reduces tree regeneration, especially under drought conditions. (4) under more extreme future climate scenarios, (4-1) fire and bark beetle severity will be less influenced by pre-disturbance fuel treatments and vegetation conditions and (4-2) regeneration of tree species will be most inhibited in vulnerable biophysical settings and following fire or beetle disturbances.3.benefitsresponding to the urgent need to reduce fuels, the USFS and state of california signed a shared stewardship agreement in 2020, which commits to treatment of 1 million acres of forest year under the guidance of the CA wildfire and forest resilience task force (wildfiretaskforce.ORG). The results from the proposed study will not only meet goals of jfsp, but also will contribute to new efforts to manage fuels in the region. New knowledge on multiple drivers of vegetation change will inform the frequency and type of treatments needed to maintain their effectiveness in forests affected by complex, climatically-driven disturbance regimes as well as by the direct effects of climate change. Deliverables will include workshops with FS personnel, conference and webinar presentations, field tours, graduate theses, refereed publication, and conference proceedings aimed at the management and scientific communities.4.task statement relevancythis research directly addresses the solicitation under task 1 and provides key insights into how biophysical setting, climate, and post-treatment disturbances determine vegetation change and fuel conditions over time. In remeasuring sites at which fuels have been treated 10 YRS ago, we will elucidate key drivers of fuel treatment longevity and then models these dynamics under climate change scenarios.