Evaluating Drought Impact on Postfire Recovery of Chaparral Across Southern California
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Evaluating Drought Impact on Postfire Recovery of Chaparral Across Southern California Emanuel A. Storey,1* Douglas A. Stow,1 Dar A. Roberts,2 John F. O’Leary,1 and Frank W. Davis3 1
Department of Geography, San Diego State University, 5500 Campanile Drive, San Diego, California 92182, USA; 2Department of Geography, University of California-Santa Barbara, 3611 Ellison Hall, Santa Barbara, California 93106, USA; 3Bren School of Environmental Science and Management, University of California-Santa Barbara, 2400 Bren Hall, Santa Barbara, California 93106, USA
ABSTRACT Chaparral shrubs in southern California may be vulnerable to frequent fire and severe drought. Drought may diminish postfire recovery or worsen impact of short-interval fires. Field-based studies have not shown the extent and magnitude of drought effects on recovery, which may vary among chaparral types and climatic zones. We tracked regional patterns of shrub cover based on June-solstice Landsat Normalized Difference Vegetation Index series, compared between the periods 1984–1989 and 2014–2018. High spatial resolution ortho-imagery was used to map shrub cover in distributed sample plots, to empirically constrain the Landsat-based estimates of mature-stage lateral canopy recovery. We evaluated precipitation, climatic water deficit (CWD), and Palmer Drought Severity Index in summer and wet seasons preceding and following fire, as regional predictors of recovery in 982 locations between the Pacific Coast
Received 14 August 2019; accepted 15 August 2020 Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-020-00551-2) contains supplementary material, which is available to authorized users. Author Contributions ES took primary responsibility for the research design, analysis, and writing; DS assisted in research formulation and design, and took a secondary role in writing; DR added to the literature review, design of graphics, and editorial tasks; JO assisted in field work and manuscript editing; FD contributed to analytical design and theoretical conception of the work. *Corresponding author; e-mail: [email protected]
and inland deserts. Wet-season CWD was the strongest drought-metric predictor of recovery, contributing 34–43% of explanatory power in multivariate regressions (R2 = 0.16–0.42). Limited recovery linked to drought was most prevalent in transmontane chamise chaparral; impacts were minor in montane areas, and in mixed and montane chaparral types. Elevation was correlated negatively to recovery of transmontane chamise; this may imply acute drought sensitivity in resprouts which predominate seedlings at higher elevations. Landsat Visible Atmospherically Resistant Index (sensitive to live-fuel moisture) was evaluated as a landscape-scale predictor of recovery and explained the greatest amount of variance in a multivariate regression (R2 = 0.53). We find that drought severity was more closely related to recovery differences among twice-burned sites than was fire-return interval. Summarily, drought h
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