Keeping up with Climate Change: Assessing the Vulnerability of Eucalyptus Species to a Changing Climate in the South-West of Western Australia
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Keeping up with climate change: assessing the vulnerability of Eucalyptus species to a changing climate in the south-west of Western Australia Jason J. Hamer BSc. (Environmental Biology) BSc. (Honours) - First Class Honours This thesis is presented for the degree of Doctor of Philosophy The University of Western Australia Faculty of Science School of Plant Biology 2015 Statement of candidate contribution The research presented in this thesis is an original contribution to the field of Plant Biology. The poetry, hypotheses and experiments presented and discussed in this thesis are my own original ideas and writing. Others who made significant contributions to the research are acknowledged in the section: “Publications arising from this Thesis”. Permission has been obtained from all co-authors to include these publications in this thesis. This thesis has been completed during the course of enrolment in a Doctorate of Philosophy at The University of Western Australia, and has not been used previously for a degree or diploma at any other institution. … ……….. Jason J. Hamer 17th August 2015 Michael Renton (coordinating supervisor) 17th August 2015 i Climate Change and the Poor Gum Tree An Australian bush poem by Jason J. Hamer Today I have a story to tell, Summarising my PhD. This bush poetry has been three years in the making, And it’s about our iconic gum tree. And if you pay quite close attention, There’ll be something interesting you’ll find. As I only have four beats per line The statistics won’t be a grind! Now, right around the world you see, There are woodlands in decline. From Europe to America and in Australia, This is surely one big sign. These trees are starving with closed stomata, And pests are eating them out. They’ve bubbles that grow as xylem collapse, We can only blame the drought. The effects are worldwide, but they really hit home When they encroach on our diverse hotspot. My poor gum trees, the king of the woods, They are already suffering root rot! So some modelling was done into species distribution To find to what extent they’re in danger. And as it turns out they are required to shift, With very little luck I’ll wager. The arid species appear most at risk, With their climate envelope quite narrow. The gum trees just don’t have the dispersal tricks; Their seed can’t fly like an arrow. “But what am I to do?” said the poor gum tree “I can’t pick up my feet!” “For the climate is shifting and the rain depleting, It’s not just a walk down the street” So I set out to find how vulnerable he is – My poor, stranded gum tree. I looked high and low, from micro to macro, I worked hard, you won’t disagree. ii I looked down at his roots as these are what bind him – It seemed a good place to start. I observed their root architecture, and believe it or not, I could tell the species apart! Those typically in sand had plenty of roots, Exploring a large lateral section. But the clay-bound species focused all their energy, To grow in a downward direction. But the problem was they didn’t appear plastic, Clay species couldn’t compete in sand. So if they did move they might not survive, They will probably need a hand. Next step, I shifted my gaze further up, Studying the branch and leaves. With the anatomy and structure of these components Physiology I could perceive. Vein length, Huber value and leafing intensity, Conductivity of xylem and stomata. You sure showed me, for what I found Was not what I expected from the data. Though you're well adapted to current conditions, These are likely to change quite soon. With larger climate ranges it seems more likely It’s the wetter species that’ll attune. “Where next?” he asks, still standing root bound. “You won’t just leave me here?” “PhD is all done and you are on the run” “Is my fate just to disappear?” Unfortunately for you your future may rest, In the coal-stained hands of mankind. For the best solution to ensure you survive Is to show our fates intertwined. For we are more alike than you may think, My brave, good hearted gum tree. We can rhyme all we want but if nothing is done, We have, nowhere else, to flee. iii Thesis abstract Under the influence of global climate change, the area experiencing a Mediterranean climate in the south-west of Western Australia – of which a large portion is classified as a biodiversity hotspot – is predicted to decrease by up to 51% by the year 2100. The increase in temperature and decrease in precipitation in this region has already caused large scale health decline in Eucalyptus species in a number of woodlands in more mesic climates. As eucalypts are the dominant overstorey species in many habitat types in the region and provide many ecosystem services, the large scale loss of the species would likely result in significant changes to community composition. Thus, it is necessary to increase our understanding of the vulnerability of Eucalyptus species to a changing climate so that we can better conserve these species and the flora and fauna that depend on them. In this thesis, vulnerability is defined as the combination of a species’ exposure to climate change, its resilience to change and its adaptive capacity. These components of vulnerability are explored in the context of species’ current distribution patterns, as understanding how a species is currently adapted to its current climate can allow us to predict what future distributions may look like. Exposure to climate change was quantified using species distribution modelling techniques to predict the percentage of species’ current distribution that will no longer be suitable for species’ survival. Above and below ground plant functional traits that contribute to both species’ resilience to change and adaptive capacity were then quantified to improve our understanding as to how these species have adapted across an existing aridity gradient. Results suggest that species in more arid conditions will have a greater proportion of their habitat exposed to unfavourable conditions compared to mesic species, with some predicted to lose all suitable habitat. Though the shallow climate gradients of inland Western Australia result in large distribution ranges for these species, it also means that, in comparison to more mesic species, a given change in climate will result in a larger proportion of their distribution becoming unsuitable. As these species are unlikely to be able to migrate fast enough to keep up with the changing climate, the high level of exposure faced by many species means that species’ sensitivity and adaptive capacity are very important for long term survival. In terms of above ground traits, species in more arid conditions appear to be well adapted to current climate conditions, with important traits showing some degree of plasticity within species. This was observed as a decrease in vessel diameter, increase to sapwood density and leaf mass per area and a decrease in leaf size across an aridity gradient, all of which confer a reduced sensitivity to hydraulic failure in water-limited environments. Though the combination of the above traits resulted in more arid species having lower xylem conductivity, this was balanced by an increase in sapwood area to leaf area ratio, maintaining total stomatal conductance to xylem conductivity ratios across the aridity gradient. However, in a rapidly changing climate, species may not have enough time to adapt and change their average trait values to those of species that replace them iv along the aridity gradient. Even if species could migrate to new locations, seedling root architecture of species typically growing in finer-textured soil (such as many arid Eucalyptus species) may not be suitable for establishment in a coarser-textured soil (more typical of the regions to which they would likely need to migrate). This is because species typically growing in fine-textured soil tend to invest most resources into producing a taproot, with minimal lateral roots produced. This is likely to be a disadvantage in a coarser-textured (a soil with lower-water holding capacity), for which more lateral roots are likely to be needed to be able to explore a large enough soil volume for water. Thus, due to the combination of a high exposure to climate change and local root system adaptation to predominantly fine textured soils, Eucalyptus species in more arid environments are likely to be at greater risk to a changing climate than those living in a more mesic climate. These findings suggest that our research, restoration and conservation efforts should not focus disproportionally on more coastal higher rainfall species which occur conveniently close to human population centres; rather, consideration should be given to those species further inland where the greater impacts may actually occur. v Publications arising from this thesis In accordance with The University of Western Australia guidelines, this thesis has been prepared as a series of publications proceeded by a general introduction and followed by a general discussion. As such, it contains published manuscripts and manuscripts prepared for publication, all of which have been co-authored. The bibliographical details of the published work and where it appears in the thesis are outlined below. Published manuscripts: Hamer J.J., Veneklaas E.J., Poot P., Mokany K., Renton M. (2015) Shallow environmental gradients put inland species at risk: Insights and implications from predicting future distributions of Eucalyptus species in South Western Australia. Austral Ecology 40:923- 932. DOI: 10.1111/aec.12274 This publication forms Chapter 2 of this thesis.