Aim: Climate warming is increasing fire activity in many of Earth's forested ecosystems. Because fire is an important catalyst for change, investigation of post-fire vegetation response is crucial for understanding the potential for future conversions from forest to non-forest vegetation types. To better understand effects of wildfire and climate warming on forest recovery, we assessed the extent to which climate and terrain influence spatiotemporal variation in past and future post-fire tree regeneration. Location: Montane forests, Rocky Mountains, USA Time Period: 1981-2099 Taxa Studied: Pinus ponderosa; Pseudotsuga menziesii Methods: We developed a network of dendrochronological samples (n = 717) and field plots (n = 1301) from post-fire environments spanning a range of topographic and climatic settings. We then used boosted regression trees to predict annual suitability for post-fire seedling establishment and generalized linear mixed models to predict total post-fire seedling abundances, reconstructing recent trends in post-fire recovery and projecting future dynamics using three general circulation models (GCMs) under moderate and extreme emission scenarios. Results: Though 1981-2015 declines in growing season (April-September) precipitation were associated with declining suitability for seedling establishment, 2021-2099 trends in precipitation were widely variable among GCMs, leading to mixed projections of future establishment suitability. In contrast, climatic water deficit (CWD), strongly tied to warming temperature and increased evaporative demand, was projected to increase throughout our study area. Our projections strongly suggest that future increases in CWD and an increased frequency of extreme drought will reduce post-fire seedling abundances. Main Conclusions: Our findings highlight the key roles of warming and drying in declines in forest resilience to wildfire. The striking differences in projections of post-fire recovery between moderate and extreme emissions scenarios suggest that the most extreme impacts on forest resilience in the latter part of the 21st century may be mitigated with aggressive emissions reductions in the next two decades.
|Date made available||Jan 6 2022|