Rare drought-induced mortality of juniper is enhanced by edaphic stressors and influenced by stand density

During 2001-2003, a severe sub-continental drought resulted in a mortality event involving multiple woody plant species. Mass-mortality (up to 65% mortality in the locality studied) of the most drought resistant tree in the region, Juniperus monosperma (Engelm)Sarq., resulted in a conspicuously heterogeneous dieback pattern. Mortality was over three times greater in grassland landscapes compared to adjacent woodlands. We investigated the relative importance of biotic stressors (abundance of grass, tree density), edaphic stressors (soil texture), and climatic stressors (heat load) in determination of mortality. Using a multivariate modeling approach we separated the correlated edaphic and climatic influences, and determined that soil texture was the primary driver. We hypothesize that hydraulic failure in juniper was influenced by small-scale variation in matrix water potential (ψ_m). Density of tree stands also exerted an apparent competitive effect in grasslands and an apparent facilitative effect in woodlands. This study offers a rare glimpse of the extreme drought response of an anisohydric tree. The characteristics of sites with high juniper mortality may allow insight into the consequences of climate change impacts, enabling prediction of the types of sites which may be affected in the future.