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Patterns of tree dieback in Queensland, Australia: The importance of drought stress and the role of resistance to cavitation

Department of Agronomy and Range Science and Center for Population Biology, University of California, Davis, CA 95616, USA.
Oecologia (Impact Factor: 3.25). 05/2004; 139(2):190-8. DOI: 10.1007/s00442-004-1503-9
Source: PubMed

ABSTRACT During the extreme 1992-1997 El Niño drought event, widespread stem mortality, or tree "dieback", of both mature and juvenile eucalypts occurred within the tropical savannas of northeast Australia. Most of the dieback occurred in individuals of the ironbark species complex ( Eucalyptus crebra- E. xanthoclada) while individuals of the bloodwood species Corymbia erythrophloia, exhibited significantly less stem mortality. Indicative of greater water stress, predawn and midday xylem water potentials of ironbark adults and saplings were significantly more negative than predawn values of bloodwoods. The very negative xylem water potentials in ironbarks suggest that stem mortality in both adult and juvenile ironbarks results from drought-induced embolism and that ironbarks perhaps have a shallower and less extensive root system than bloodwoods. Although predawn and midday water potentials for ironbark adults and saplings were similar, a census of mature and juvenile ironbark trees indicated that mortality was higher in adult trees. Cavitation vulnerability curves indicated that ironbark saplings may be better buffered against cavitation than adult trees. If they possess smaller root systems, saplings are more likely than adults to experience low xylem water potentials, even in non-drought years. Xylem conduits produced in adult trees during periods of normal rainfall, although perhaps more efficient in water conduction, may be more vulnerable to cavitation during infrequent severe droughts.

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    • "Reports of dieback are increasingly common in native and invasive plant species globally (La Porta et al. 2008). Microorganisms are often implicated (e.g., M u e l l e r -D o m b o i s 1 9 8 7 ; Kowalski and Holdenrieder 2009; Herrero et al. 2011; Ismail et al. 2012; Mehl et al. 2013), and dieback in some tree and shrub species has been found to result from single pathogens, sometimes in the presence of stressors (Rice et al. 2004; La Porta et al. 2008; Pautasso et al. 2013; Scarlett et al. 2013; Aghighi et al. 2014). More often, causal explanations remain elusive (Houston 1992; Slippers and Wingfield 2007; Sakalidis et al. 2011; Jami et al. 2013). "
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    • "Drought and anthropogenically modified hydrological conditions may result in a range of stress induced responses in trees (e.g. Rice et al., 2004), including adaptive canopy thinning and branch sacrifice (dieback) to reduce transpiration demand and conserve hydraulic status (Tyree and Sperry, 1988; Rood et al., 2000). Extreme moisture deficit may also result in embolism, cavitation and failure in transporting xylem tissue, ultimately causing death (Tyree and Ewers, 1991; McDowell et al., 2008). "
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