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Speaker: Prof. Brendan Choat, Hawkesbury Institute for the Environment, Western Sydney University.
Severe droughts have caused widespread tree mortality across many forest biomes with profound impacts on ecosystem function and carbon balance. Climate change is expected to intensify regional scale droughts via the effects of higher temperatures and evaporative demand, with evidence suggesting that amplification of drought stress by anomalously high temperatures is already occurring. South-eastern Australia was subject to a severe drought from 2017–2020, with 2019 being both the hottest and driest year on record across the continent. This drought resulted in massive canopy die-off in forest and woodland vegetation throughout south-eastern Australia. Broadscale forest mortality events have focused attention on the physiological underpinnings of drought-induced tree death and our ability to forecast risk to forests from future extreme events. Catastrophic failure of the plant hydraulic system caused by the formation of gas emboli in the xylem is recognised as a principal mechanism associated with tree mortality during drought. Recent work has advanced our understanding of this process and identified species-specific physiological thresholds for tree death. I will explore our current understanding of tree response to drought, incorporating field data from the 2019 drought and the application of hydraulic failure thresholds to process-based models predicting mortality. At the whole plant level, developments in methodology used to evaluate the impacts of water stress on plant hydraulic function provide novel insights into hydraulic failure and mechanisms of recovery after drought.