Differential tree mortality in response to severe drought: evidence for long‐term vegetation shifts

摘要: Summary 1 Although drought frequency and severity are predicted to increase across numerous continental interiors, the consequences of these changes for dominant plants largely unknown. Over last decade, south-western US has experienced six years, including extreme droughts 1996 2002, which led widespread tree mortality northern Arizona. 2 We examined impact on co-dominant species pinyon‐juniper woodland ( Pinus edulis Juniperus monosperma ), a major vegetation type in US. 3 Pinyon following both was 6.5-fold higher than juniper mortality. In addition, large pinyons suffered 2‐6-fold greater small pinyons, pattern associated with reproductively mature trees survival smaller resulting from facilitation by established vegetation. Differential resulted shift such that woodlands becoming dominated juniper, is typical lower elevations more arid conditions. 4 Sites high pinyon during first additional second drought, so reductions densities release below-ground competition did not buffer surviving against drought. Such repeated events also suggest stands may suffer chronic stress. 5 Reductions biotic associations (e.g. avian seed dispersers, ectomycorrhizas nurse plants) will probably result ensure observed shifts be persistent. Because approximately 1000 pine, structure large-scale community consequences.