Leaf habit and plant height are associated with mortality risk of trees and shrubs during extreme drought in a Chinese savanna ecosystem

Abstract

Climate change has significantly increased the frequency and severity of droughts and risk of tree death worldwide. Differences in leaf habit, plant size, and species diversity are associated with differences in the risk of drought-induced mortality, but the relative contributions of these factors to the risk of mortality are unclear. In a study of the mortality of tree and shrub species during the extreme drought of 2019 in a savanna ecosystem in Southwest China, we assessed the relative contributions of evergreen and deciduous leaf habit, plant size, and species richness and diversity to the mortality of shrubs and trees after the 2019 extreme drought. The deciduous species had significantly lower hydraulic safety margins than the coexisting evergreen species, resulting in a higher mortality risk. Additionally, species and individuals with taller canopies tended to have deeper root systems, an advantage during extreme drought that reduced mortality risk. Notably, mortality risk was largely independent of stand species richness and diversity. Overall, leaf habit and plant height were better predictors of mortality risk than species richness and diversity. These novel insights provide a better understanding of the mechanisms driving drought-induced mortality in the ecosystems with a low canopy and weak interspecific and intraspecific competition for shared resources. Leaf habit and tree size should be incorporated into hypotheses on the mechanisms underlying drought-induced tree mortality.

Keywords

Drought-induced mortality / Hydraulic safety margin / Root depth / Savanna / Species diversity

References

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