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Wildfires and climate change push low-elevation forests across a critical climate threshold for tree regeneration

Citation

Davis, Kimberley T. et al. (2021), Wildfires and climate change push low-elevation forests across a critical climate threshold for tree regeneration, Dryad, Dataset, https://doi.org/10.5061/dryad.pc3f9d8

Abstract

Climate change is increasing fire activity in the western United States, which has the potential to accelerate climate-induced shifts in vegetation communities. Wildfire can catalyze vegetation change by killing adult trees that could otherwise persist in climate conditions no longer suitable for seedling establishment and survival. Recently documented declines in postfire conifer recruitment in the western United States may be an example of this phenomenon. However, the role of annual climate variation and its interaction with long-term climate trends in driving these changes is poorly resolved. Here we examine the relationship between annual climate and postfire tree regeneration of two dominant, low-elevation conifers (ponderosa pine and Douglas-fir) using annually resolved establishment dates from 2,935 destructively sampled trees from 33 wildfires across four regions in the western United States. We show that regeneration had a nonlinear response to annual climate conditions, with distinct thresholds for recruitment based on vapor pressure deficit, soil moisture, and maximum surface temperature. At dry sites across our study region, seasonal to annual climate conditions over the past 20 years have crossed these thresholds, such that conditions have become increasingly unsuitable for regeneration. High fire severity and low seed availability further reduced the probability of postfire regeneration. Together, our results demonstrate that climate change combined with high severity fire is leading to increasingly fewer opportunities for seedlings to establish after wildfires and may lead to ecosystem transitions in low-elevation ponderosa pine and Douglas-fir forests across the western United States.

Usage Notes

Funding

Joint Fire Science Program, Award: 16-1-01-15

National Science Foundation, Award: OISE-0966472

National Science Foundation, Award: BCS-1232997

National Science Foundation, Award: BCS-1461576

National Institute of Food and Agriculture, Award: 1012438

National Aeronautics and Space Administration, Award: NNH11ZDA001N-FIRES

Location

Northern Rockies
United States
Colorado Front Range
Northern California
Southwestern US