Seeing the Forest Through the Trees

An accurate model of leaf transpiration will make it easier to predict the effect of climate change on forests.

How do you mathematically model a tree? It might seem like an odd question, but it is a fundamental challenge facing scientists trying to find out how the environment will respond to a changing climate. 

At Western Sydney University’s Hawkesbury Institute for the Environment, Professor Belinda Medlyn and colleagues have been developing models of forests that can be used to predict how they will be affected by changes in temperature, rainfall and carbon dioxide, and how they will also affect the climate around them.

“We know the climate has already started to change, and that will have a significant impact on the vegetation across the world, but these climate-driven changes are really hard to predict because there are so many different pieces to the puzzle,” says Medlyn.

One of those pieces is the question of how much water has  transpired, or evaporated, from leaves. For the past few decades, modellers have assumed that the rate of transpiration was essentially the same across all different types of vegetation. But Medlyn took a closer look at the real-world data on water vapour transpiration from leaves, and realised something wasn’t right. So she built a new model of leaf transpiration, which accurately predicts transpiration regardless of species.

Research collaborator, Martin De Kauwe, research fellow at the Climate Change Research Centre at the University of New South Wales, says Medlyn’s model was a significant step forward, and is now incorporated into all major models of forest responses. It has also had major implications for understanding how forests respond to extreme climate events such as heat waves, he adds.

Need to know

  • Belinda Medlyn has developed a transpiration model that works across all plant species.    
  • It is now incorporated into all major models of forest behaviour.
  • This work will help researchers understand how forests respond to extreme climate events.

“We were able to show from the measurements and her model that evergreen needle-leaf forests have a more conservative water use behaviour, and that basically changes the feedback of water into the atmosphere,” he explains. The revised model, incorporating Medlyn’s work, suggests that instead of releasing water into the atmosphere during heat waves, which would lower temperatures, these forests hold on to their water, which could actually make heat waves worse. This means previous models may have underestimated the heat wave intensity across northern Europe, explains De Kauwe.

Modelling these processes requires a unique combination of skills – mathematics and ecology. Medlyn had always loved mathematics, but after starting her professional career working in a bank, realised she wanted to apply it to the natural world. “There’s a huge need for people with mathematical skills to work in areas like climate science and ecological modelling,” she says.

The transpiration model is just one piece of the puzzle: Medlyn’s overall aim is to develop models that describe forests, particularly Australian ones, and predict how they are responding to climate change, by piecing together as much evidence as possible. That includes modelling the response of forests and trees to increasing carbon dioxide, more frequent and severe drought, and of course, increasing and more severe heatwaves.

It’s a huge task, and despite the years of research already undertaken with her colleagues, Medlyn says in some ways they’re just at the beginning of the process. “I can talk to you about what happens to each of those elements, separately, but putting them together is the tricky part.”  

Meet the Academic | Professor Belinda Medlyn

I have an Honours degree in Applied Mathematics from University of Adelaide. After graduating I went to work for a merchant bank and didn't take to it at all.

Then I heard a seminar by Hugh Possingham on mathematical ecology. As a keen outdoors type, I was fascinated by the idea that one could apply mathematics to the outdoors.

I went back to university and obtained a PhD in theoretical biology from University of NSW. I then spent four years as a post-doc in Europe, where I was privileged to work closely with a number of experimentalists who taught me how to interpret data.

On my return to Australia I married, had two children, and worked part-time for several years. I'm now full-time again and am enjoying leading a productive research group.

With collaborators around the world, beautiful forests to work in, and a number of challenging research problems to work on, I have never regretted leaving finance!

Credit

This research was supported by the Australian Government through the Australian Research Council.

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Future-Makers is published for Western Sydney University by Nature Research Custom Media, part of Springer Nature.