Photo: Dead tree. Credit: Indigo Skies Photography (Flickr CC BY-NC-ND 2.0.)

Australia has recently experienced two of the worst droughts on record (Millennium Drought, 2000–2009 and Big Dry, 2017–2019), and these droughts have had major impacts on forests and woodlands, with many trees dying. Droughts and in particular, droughts coincident with heat extremes are likely to increase in the future, putting our precious forests and woodlands at further risk.

To be able to robustly project future drought impacts on Australian vegetation, we first need to be able to demonstrate that we can predict landscape-scale mortality to contemporary droughts.

In a recent study, CLEX researchers with colleagues from Hawkesbury Institute for the Environment, and James Cook University implemented a new model of plant hydraulics into the Community Atmosphere Biosphere Land Exchange (CABLE) land surface model. They constrained the vegetations’ sensitivity to drought using hydraulic and physiological traits measured in a manipulative drought experiment conducted on Australian tree species originating from across wide rainfall gradient (118-1125 mm yr-1).

The model predictions of where and when trees may have died across South East Australia agreed well with estimates derived from satellites of regions experiencing the greatest impact of drought. The model predictions can now be further compared to data collected by a citizen science initiative – the Dead Tree Detective. This next step is important because despite the model projecting significant impacts of water stress across the landscape, the model also implied significant resilience of Australian tree species to drought. This projection may be at odds with some localised reports of mortality and so exploring the model projections at these site scales is an important future direction.

This work shows that it is now possible to predict the risk of tree death – at large scales (~400,000 km2) and this could have important consequences for conservation and management of Australian forests and woodlands.

  • Paper: De Kauwe, M.G., Medlyn, B.E., Ukkola, A.M., Mu, M., Sabot, M.E., Pitman, A.J., Meir, P., Cernusak, L., Rifai, S.W., Choat, B., Tissue, D.T., Blackman, C.J., Li, X., Roderick, M. and Briggs, P.R. (2020), Identifying areas at risk of drought‐induced tree mortality across South‐Eastern Australia. Glob Change Biol. Accepted Author Manuscript. doi:10.1111/gcb.15215.