Project Title: Modelling Environment and Tree Water Use
Superviser: Professor Derek Eamus, UTS
PhD conferred: 2011
Rhys Whitely completed his undergraduate BSc in Applied Physics at UTS. In his honours year he worked on a nanotechnology project on X-ray diffraction. A decision to pursue a PhD with a large biology component may seem unusual but Rhys’ research with Professor Derek Eamus in the Plant Functional Biology and Climate Change Cluster (C3) has proved that crossing scientific disciplines can often yield unexpected results.
“I did have a bit of a hill to climb. I had no biology knowledge and it was a reality check in many ways because having studied physics I used to think I was at the top of the science tree! But you need a bigger picture to work in research and now I can see the connections, how the different aspects of science fit together. My background in physics and mathematical modelling has been an asset.
Initially I was set to pursue statistical questions on soil-vegetation-atmosphere models - how to improve estimates, measuring the level of uncertainty in forecasting environmental effects, etc. However, this focus has now shifted to being more about the biology and being able to model the environment correctly, which is something I feel is not only more important, but more relevant.
My research has actually fallen into two parts. When I first started my project I needed to build my biological knowledge up from what it was and I also needed to look at what models were already out there. I began by looking at the role water plays in the environment, and as a valuable resource. I realised the importance of developing water budgets at the local and regional scales especially in a country like Australia. This led me to looking at models that describe the water used by trees; a process known as transpiration. I was directed towards the Penman-Monteith equation; an equation that has been used for over 30 years to calculate tree water-use by assuming a forest is one big leaf. I found this model to be robust and to work well as long as you had the right information about the ecosystem you were working with. Playing around with this model, I began to see that there could be an easier way to get the same answers using a simpler process, without needing such intimate ecophysiological knowledge. I’d been using a sub-model required by the Penman-Monteith equation which described what was happening at the scale of a leaf. The principle by which it worked looked like it could be applied to a much larger scale. Out of curiosity I simply took this leaf model and applied it directly to the forest scale. The results showed it to be very successful. Not only that, it required less data and was a much simpler variation on the Penman-Monteith equation. This was an exciting discovery to make so early on in my project , as I had developed something that not only worked, but was also applicable to science and industry. Since then, I have applied the model across a range of different ecosystems with great success. Although this wasn’t an original goal in my project, it has turned into something I feel is important and I hope that my model will be able to contribute something to the scientific community.
The other part of my research has more to do with the other side of the equation in modelling the amount of carbon taken up by trees. Specifically this work is concerned with modelling both the water and carbon budgets of a northern Australian sub-tropical savanna. The ability to make such predications is essential as savannas contribute approximately 25% of Australia’s land cover and hence contribute quite significantly to the carbon cycle of Australia. The uniqueness of the savanna is that they are made up of two different carbon assimilation processes that have developed over time as evolutionary strategies in reducing water loss and maximising carbon gain. These two strategies are vegetation specific; trees follow a photosynthetic pathway known as C3, and grasses follow the C4 pathway. Both processes have differing ecophysiological requirements, and the impacts of climate change have the potential to shift the balance between both carbon sinks. My work has been concerned with using a soil-plant-atmosphere model known as SPA to investigate physiological and climate change questions concerning the C3 and C4 photosynthetic processes. Some of the questions that I am looking at are the effects of changing temperature, rainfall patterns and the changing contribution of vegetation types. Answers to these kinds of questions not only have the potential to tell us what the impacts will be on regional water and carbon budgets, but also to show the conservation, cultural and economic value savannas have in Australia.
One of the great aspects of working with Derek and his team is the diversification of the research. The result is somewhat like individual pieces of a puzzle being put together to complete a bigger picture. Derek is also well connected to a large ecophysiology network which has been a great advantage – you can talk and exchange ideas and get help when you need it.
Where to now?
The results of my research were in many ways unexpected and I definitely think that my physics background helped me not only from a mathematical modelling sense but also because I was able to ask a different set of questions to a biologist.
Five years of academic research have not only consolidated my mathematical modelling skills but I’ve also learnt a lot about project and time management and teamwork. I plan to submit my thesis at the end of this year (2009) and am looking forward to the next stage in my career.”