A hydraulic framework for understanding mechanisms of woody plant survival and mortality during drought

Drought-related mortality is currently a widespread phenomenon that may become even more common with changes in climate.  In this presentation we review the evidence for a hydraulic basis of survival and mortality during drought, and present a framework from which mortality may be examined.  According to the model of Sperry and colleagues, hydraulic failure, or the point at which a plant can no longer transport water, is based on the interaction of soil, rhizosphere and xylem conductance and the driving force of soil and atmospheric water content.  When examined in this context, it appears that mortality may occur from a variety of proximal mechanisms, including outright hydraulic failure or a cascade of impacts resulting from the avoidance of hydraulic failure, such as carbon starvation and reduced resistance to pathogen or insect attack.  The hydraulic framework allows mechanistic interpretation of the multiple mechanisms, all of which are supported by empirical evidence.