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.

1 Follower
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Xylem vulnerability to cavitation and response of water potential (Ψ), stomatal conductance (g s), and net photosynthesis (P n) to drought are potentially important mechanisms of drought resistance. We compared Ψ, g s, P n, and cavitation vulnerability of shoot and root xylem among co-occurring ponderosa pine (Pinus ponderosa var. scopulorum Dougl. Ex Laws.), pinyon pine (Pinus edulis Engelm.), and Utah juniper (Juniperus osteosperma [Torr.] Little) at a forest-woodland ecotonal site in northern Arizona to elucidate drought resistance mechanisms of these species. Juniper shoots partly regulated Ψ during drought via stomatal closure, but regulation was weaker than that for ponderosa and pinyon pines, which had similar water relations and P n responses to drought. Midday g s and P n during summer drought were positive for juniper (g s = 14.3 mmol m−2 s−1, P n = 1.23 μmol m−2 s−1) but near zero for ponderosa (g s = 0.7 mmol m−2 s−1, P n = −0.02 μmol m−2 s−1) and pinyon (g s = 1.5 mmol m−2 s−1, P n = −0.18 μmol m−2 s−1) pines. Cavitation vulnerability of shoots and roots was lower for juniper than for both pines. The water potential inducing 50% loss in xylem hydraulic conductivity (Ψ50) for juniper was 5.0 MPa more negative for shoots and 3.9 MPa more negative for roots compared with the respective tissues of the pine species. Pinyon pine (Ψ50 = −2.71 MPa) was slightly more vulnerable to cavitation than ponderosa pine (Ψ50 = −3.42 MPa) for shoots, whereas root vulnerability was similar for both pines (Ψ50 = −1.69 MPa for pinyon; −1.98 MPa for ponderosa). Roots of all species were more vulnerable to cavitation than shoots. Our results show an important role of cavitation vulnerability in the greater drought resistance of Utah juniper than pinyon and ponderosa pines but not for the presumed greater drought resistance of pinyon pine than ponderosa pine.
    Forest Science 10/2013; 59(5):524-535. DOI:10.5849/forsci.12-053 · 1.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Under future climate drought-induced tree mortality may result in the contraction of species ranges and the reorganization of community composition where abundant and peripheral species exchange their patterns of dominance. Predicting these changes will be challenging because the future suitable habitat may be a mismatch for the current bioclimatic envelope because of discrepancies between the realized and fundamental niche. Here we evaluate the extent of the discrepancy, as applied to tree species in relation to their relative field-recorded drought sensitivities and their observed range-wide environmental moisture envelopes. The hypothesis tested was that different species levels of drought-induced damage at sites where they co-occur will be positively associated with the minimum moisture availability in the most drought-prone part of each species current geographic range. We tested the hypothesis using drought damage measurements for 13 Australian Myrtaceae (including Eucalyptus) tree species at a site where all co-occur, together with 120 years of climate data across their geographical ranges. With limited statistical power the results generated only modest support for the hypothesis suggesting limited capacity to predict future distributions under climate change scenarios. In spite of the poor dispersal capacities of Eucalyptus and allied genera, but consistent with knowledge of breeding systems and genetic variability within Eucalyptus, the findings also suggest that many species have a capacity for rapid adaptive response to climate change, including the vicissitudes of the late Quaternary.
    Austral Ecology 03/2014; 39(5). DOI:10.1111/aec.12125 · 1.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Groundwater decline is widespread, yet its implications for natural systems are poorly understood. Previous research has revealed links between groundwater depth and tree condition; however, critical thresholds which might indicate ecological ‘tipping points’ associated with rapid and potentially irreversible change have been difficult to quantify. This study collated data for two dominant floodplain species, Eucalyptus camaldulensis (river red gum) and E. populnea (poplar box) from 118 sites in eastern Australia where significant groundwater decline has occurred. Boosted regression trees, quantile regression and Threshold Indicator Taxa Analysis were used to investigate the relationship between tree condition and groundwater depth. Distinct non-linear responses were found, with groundwater depth thresholds identified in the range from 12.1 m to 22.6 m for E. camaldulensis and 12.6 m to 26.6 m for E. populnea beyond which canopy condition declined abruptly. Non-linear threshold responses in canopy condition in these species may be linked to rooting depth, with chronic groundwater decline decoupling trees from deep soil moisture resources. The quantification of groundwater depth thresholds is likely to be critical for management aimed at conserving groundwater dependent biodiversity. Identifying thresholds will be important in regions where water extraction and drying climates may contribute to further groundwater decline.
    12/2014; DOI:10.1016/j.gecco.2014.09.002

Full-text (2 Sources)

Available from
Jun 4, 2014