Skip to main content
ARS Home » Plains Area » Las Cruces, New Mexico » Range Management Research » Research » Publications at this Location » Publication #179170
Title: PATTERNS OF TREE DIEBACK IN QUEENSLAND, AUSTRALIA: THE IMPORTANCE OF DROUGHT STRESS AND THE ROLE OF RESISTANCE TO CAVITATION

Author
item RICE, KEVIN - UNIVERSITY OF CALIFORNIA
item MATZNER, STEVEN - AUGUSTANA COLLEGE
item BYER, WILLIAM - DAVIES LAB, CSIRO
item BROWN, JOEL - USDA-NRCS (COLLABORATOR)

Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2004
Publication Date: 4/1/2004
Citation: Rice, K.J., Matzner, S.L., Byer, W., Brown, J.R. 2004. Patterns of tree dieback in Queensland, Australia: the importance of drought stress and the role of resistance to cavitation. Oecologia. 139(2):190-198.

Interpretive Summary: Forest dieback is a recurring phenomenon that has been reported from a variety of woodland and forest communities in many parts of the world. Dieback is characterized by rapid defoliation and progressive stem mortality in overstory trees and has been attributed to a wide range of potential causes. In Australia, tree or eucalypt dieback occurs in a number of woodland and savanna habitats throughout the continent. Although dieback events in the late nineteenth and early twentieth centuries were primarily in southern locations on the continent, diebacks occurring within Australia in the last 50 years are now more widespread. Using scientific records and historical accounts, the occurrence of dieback has been related to the severe droughts Australia has experienced periodically during the last 150 years. These El Niño drought events have had a significant effect on Australian savanna structure and composition, as well as the fauna associated with these habitats. Some researchers have questioned the primary role of drought as the factor initiating dieback. However, the most widely accepted view is that drought stress causes dieback directly by inducing cavitation and also renders the tree more susceptible to insect attack and pathogens. To better understand the causes underlying these apparent differences in dieback, we conducted a study that combined field surveys of stem mortality with ecophysiological measurements of drought stress and cavitation resistance. In particular we were interested in: (1) documenting whether there were differences in stem mortality among species and among age classes within a species, and (2) exploring the possibility that these differences were related to differences in drought stress or drought tolerance, or both.

Technical 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 nondrought 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.