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

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.

Factors Determining Mortality of Adult Chaparral Shrubs in an Extreme Drought Year in California

“…Rice et al (2004) reported that during the extreme 1992-1997 El Niñ o drought period in Queensland, Australia, tree species with greater resistance to xylem cavitation showed the most dieback, which they attributed to shallower root systems. In response to a record drought in 2007 in central North Carolina, USA, tree species with the greatest resistance to cavitation showed the greatest canopy dieback (Hoffmann et al 2011), which the authors attributed both to greater leaf retention and shallower root systems in the cavitation-resistant species.…”

The incorporation of extreme drought events improves models for beech persistence at its distribution limit

“…However, hydraulic failure is difficult to trace in the field. Lower resistance to cavitation (Rice et al 2004) and lethal leaf dehydration (Kursar et al 2009) have been related to increased mortality in other species, rendering hydraulic failure a very plausible mechanism for observed tree mortality under severe, acute drought. A drawback of the EDM is that well-documented system tip-outs are sparse in space and time; therefore, such models are based on local data.…”

Increasing Drought Sensitivity and Decline of Atlas Cedar (Cedrus atlantica) in the Moroccan Middle Atlas Forests

“…Therefore, the first basal area increment value in our time series is: BAI1= BA1 − BA0 = π × (RadIB − CL + TRW1) 2 − π × (RadIB -CL) 2 ; the second one is:…”