Response of Sierra Nevada forests to projected climate–wildfire interactions

Abstract

Climate influences forests directly and indirectly through disturbance. The interaction of climate change and increasing area burned has the potential to alter forest composition and community assembly. However, the overall forest response is likely to be influenced by species-specific responses to environmental change and the scale of change in overstory species cover. In this study, we sought to quantify how projected changes in climate and large wildfire size would alter forest communities and carbon (C) dynamics, irrespective of competition from nontree species and potential changes in other fire regimes, across the Sierra Nevada, USA. We used a species-specific, spatially explicit forest landscape model (LANDIS-II) to evaluate forest response to climate-wildfire interactions under historical (baseline) climate and climate projections from three climate models (GFDL, CCSM3, and CNRM) forced by a medium-high emission scenario (A2) in combination with corresponding climate-specific large wildfire projections. By late century, we found modest changes in the spatial distribution of dominant species by biomass relative to baseline, but extensive changes in recruitment distribution. Although forest recruitment declined across much of the Sierra, we found that projected climate and wildfire favored the recruitment of more drought-tolerant species over less drought-tolerant species relative to baseline, and this change was greatest at mid-elevations. We also found that projected climate and wildfire decreased tree species richness across a large proportion of the study area and transitioned more area to a C source, which reduced landscape-level C sequestration potential. Our study, although a conservative estimate, suggests that by late century, forest community distributions may not change as intact units as predicted by biome-based modeling, but are likely to trend toward simplified community composition as communities gradually disaggregate and the least tolerant species are no longer able to establish. The potential exists for substantial community composition change and forest simplification beyond this century.

Post‐fire forest regeneration shows limited climate tracking and potential for drought‐induced type conversion

“…, Campbell and Shinneman , Liang et al. ). As one exception, the response of broadleaved trees to the anomaly term reflecting mean (but not minimum) post‐fire precipitation did show a weak signal of climate tracking: recruitment responded negatively to post‐fire precipitation in dry sites and positively in wet sites (Appendix : Fig.…”

“…Simulation models (Campbell and Shinneman , Liang et al. ) and projections based on contemporary climate associations (Tepley et al. ) also generally predict declines in conifer recruitment with increasing aridity at hot, dry range limits but not necessarily expansion at cool, wet range limits, where colonization of new sites may be poor due to dispersal limitation and/or limited availability of suitable sites.…”

Observed Impacts of Anthropogenic Climate Change on Wildfire in California

“…The effects of anthropogenic climate change on California's fire regimes are likely to be diverse and complex, varying by region and season (Liang et al, 2017;Pierce et al, 2018;Syphard et al, 2019;Westerling, 2018). Climate model projections of warming and increased atmospheric aridity in California are strong and robust across models (Pierce et al, 2013).…”

Integrating Species‐Specific Information in Models Improves Regional Projections Under Climate Change

“…Extreme drought and insect outbreaks disproportionately affect some species (e.g. Severe wildfire can act as a catalyst for biome change when dominant species are killed (Liang et al, 2017a). Severe wildfire can act as a catalyst for biome change when dominant species are killed (Liang et al, 2017a).…”