Exploring drought resilience in Australian tree species.

Abstract

Global climate change is challenging many forested ecosystems with elevated temperatures and increasingly severe and frequent drought, heat waves, and outbreaks of biotic agents. Escalating forest dieback occurrences in response to changing abiotic and biotic pressures have significant implications for ecosystem structure, biodiversity, and terrestrial fluxes of carbon and water. This thesis comprises a compilation of four independent studies exploring the contribution of hydraulic and water relations traits to drought resilience and vulnerability in Australian tree species. Chapter 1 focuses on novel pathways of top-down tree rehydration from atmospheric water sources in two mangrove species of the Sonneratia genus, and variability in the conductance of these pathways due to seasonality and dehydration. Chapter 2 explores the contribution of dry season acclimation of traits influencing water use and water storage to the maintenance of gas exchange and mitigation of loss of hydraulic function in the mangrove Sonneratia alba. Chapter 3 explores variation in drought and structural traits among two snow-gum subspecies (Eucalyptus pauciflora subsp. pauciflora and Eucalyptus pauciflora subsp. niphophila) and trait associations with elevation-dependent spatial patterns of wood borer-mediated dieback in Australia's subalpine woodlands. Finally, Chapter 4 explores the cross-tolerant effects of salinity gradients and leaf dehydration on photosynthetic (PSII) heat tolerance in twelve mangrove species distributed along a salinity gradient. These chapters provide evidence of spatial and seasonal variation in trait expression and their interactions with plant-water balance and drought resilience within and between species. For many unmanaged forests, greater resolution of these complex biotic-environmental interactions will be essential for the reliable modelling and effective management of forest resilience under future climates. Show more