Page 8 Decision Point #72 - August 2013 Eucalypts are iconic trees in Australian landscapes, and given the variety of treed landscapes that are found across Australia, that’s an amazing thing to consider. There are around 800 species (eucalypt taxonomy is a moveable feast) of three genera, Eucalyptus, Corymbia and Angophora that together are known as eucalypts or gum trees, and these trees have dominance or co-dominance in most forest and woodland ecosystems in Australia. You’ll find them in rainforests, up mountains and across the arid zone. And, in all these places, eucalypts are providing a range of essential resources for other animals and plants as well as generating ecosystem services such as climate regulation, water security and carbon sequestration and storage. How will this important group of trees cope with climate change? Trees are among the first groups to be affected globally by climate change as they are particularly vulnerable due to long generation times and short dispersal distances. In the northern hemisphere there’s been considerable research on the projected impacts of climate change on species and ecosystems but that’s not the case with southern- hemisphere ecosystems. Working with Laura Pollock (University of Melbourne) and Clive McAlpine (University of Queensland), I recently led the first comprehensive investigation into the vulnerability of eucalypt distributions to climate change across Australia. The findings of our analysis should be out soon but here’s an overview of what we discovered. While our findings focussed on Australian systems, they have important implications for many other southern hemisphere regions, such as sub- tropical and tropical savannas with seasonally variable rainfall. These occur widely across Africa, South America and the Asian subcontinent. A continental-scale analysis As those of us who live here are well aware, Australia’s climate is unique in its high variability, with most of the continent water-limited (apart from during floods and rainstorms!). The additive combination of changes in temperature and rainfall will govern the likely impacts we will experience from climate change. Climate projections indicate that fluctuations in temperatures and rainfall will increase over time. They will also increase the further Give me a home among the gum trees But what if those gum trees lose their home to climate change? By Nathalie Butt (University of Queensland) you move away from the coast. This means that the continental interior will become hotter and drier faster than other areas. Available moisture is projected to decrease which will affect evaporation and evapotranspiration. This transition to a hotter and more drought-prone climate represents a major risk for Australia’s ecosystems, particularly for those without the capacity to recover or adapt. So, how best to carry out a continental-scale analysis, accounting for climate and geographical variation? We used the climate classes from the Bureau of Meteorology to identify four broad bio-geographical regions, each with four climate region sub groups. We selected representative eucalypt species for each climate region, each community role (where the species status is either dominant, typical or endemic) and each type of range breadth (wide/narrow/local). We also included a ‘wide-range’ group of species whose distributions were not closely linked to any of the climate regions (Figure 1). Figure 1: Proportional pixel losses and gains by climate regional group (each region includes four climate subgroups), calculated from the 2085 time step for both scenarios (moderate and extreme). The lines with solid circles represent group ranges and means for the extreme scenario; the lines and hollow circles show the group ranges and means for the moderate scenario. One country, many eucalypt-dominated ecosystems. Pictured below are examples of some of the shapes and forms of gum trees across Australia and the ecosystems they influence. Climate change could have profound impacts on many of them.