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 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 has a major role in long-term shrub cover reduction within xeric chaparral ecotones bounding the Mojave Desert and Colorado Desert, likely in tandem with other global change stressors.

加利福尼亚南部的丛林灌木可能容易遭受频繁的大火和严重的干旱。干旱可能会减少火灾后的恢复或使短间隔火灾的影响加剧。野外研究尚未显示干旱对恢复的影响的程度和严重程度，在不同的牧区类型和气候区之间可能有所不同。我们根据1984年至1989年与2014年至2018年之间的6月至Landsat归一化差异植被指数系列，跟踪了灌木覆盖的区域格局。高分辨率空间正射影像用于在分布的样地中绘制灌木覆盖图，以经验方式限制基于Landsat的成熟阶段侧向冠层恢复的估算。我们评估了火灾前后夏季和雨季的降水，气候缺水（CWD）和Palmer干旱严重度指数，作为太平洋海岸带和内陆沙漠之间982个地点恢复的区域性预测指标。湿季CWD是最强的干旱指标恢复指标，在多元回归分析中贡献了34–43％的解释力（R ²  = 0.16-0.42）。与干旱有关的恢复有限在跨山顶的丛林中最为普遍。在山地地区以及混合和山地牧区类型中影响较小。海拔高度与跨山cha的恢复呈负相关；这可能意味着在高海拔地区占主导地位的幼苗中，新芽对急性干旱敏感。Landsat可见大气抵抗指数（对活燃料的水分敏感）被评估为景观尺度恢复的预测指标，并解释了多元回归中最大的方差（R ² = 0.53）。我们发现干旱严重程度与两次烧毁地点之间的恢复差异相比，与回火间隔之间的关系更为密切。总体而言，干旱在限制莫哈韦沙漠和科罗拉多沙漠的干湿性丛林交错带内长期减少灌木覆盖方面起着重要作用，这很可能与其他全球变化压力共同作用。