The Big Picture
Climate clearly plays an incredibly strong role in determining what trees can grow where. With climate changing, the world’s forests are very likely to change too. The question our group tackles is this: Can we predict what forests will grow where, and how fast they’ll grow – now and into the future? It’s a big, difficult question, because there are so many different factors involved – atmospheric CO2 concentration, temperature, humidity, drought, and species type, to name just a few! There currently are no believable projections for the likely effects of changing climate on Australian forests and woodlands (see our 2011 report), which means that most Australian land managers are ‘flying blind’. To make such predictions, we are developing computer models based as much as possible on the evidence from ecological and physiological studies of how trees and forests function. We work closely with experimentalists studying forests, at the Hawkesbury Institute and around the world.
Some of Our Research Projects
Brown is the new green: Grassland responses to drought and heat (2018 – 2020) ARC Discovery project; CI’s Belinda Medlyn, Elise Pendall, Sally Power, David Tissue; PI’s Alan Knapp, Melinda Smith (Colorado State University) Grassland ecosystems are important reservoirs of global biodiversity and carbon storage. Grasslands are highly sensitive to drought and heat stress, but we recently showed that current grassland models cannot predict these responses because they do not adequately represent the key processes of physiological drought tolerance, leaf browning, and species traits. We will capitalise on new experimental infrastructure (such as PACE, DriGRASS, DroughtNet) to collect targeted data sets in order to develop and test model representations of these key processes. Our goal is to greatly increase capacity to predict the impact of drought and heat stress on grasslands, at scales ranging from field to globe.
To grow or to store: Do plants hedge their bets? (2016 – 2018) ARC Discovery project; CI’s Belinda Medlyn, Remko Duursma, Roderick Dewar (Australian National U), Mat Williams (U Edinburgh) This project aims to resolve a long-standing question about the function of perennial plants: how much of the carbon taken up by photosynthesis is used immediately for growth, and how much is kept in reserve as insurance against future stress? This question is fundamental to our understanding of how plants respond to stresses such as insect infestation and severe drought, and yet lack of data and theoretical modelling currently hampers our ability to answer it. By applying novel data analysis and modelling tools to recent experimental results, we will test alternative hypotheses for how plants allocate carbon between growth and storage in response to stress.
Identifying regions of high drought mortality risk for tree species in New South Wales (2015 – 2017) ARC Linkages project with Office of Environment and Heritage and Macquarie University; CI’s Belinda Medlyn, Linda Beaumont, Brad Evans, David Tissue, Remko Duursma, Paul Rymer, Mark Tjoelker, Tony Auld, Brendan Choat, Martin De Kauwe
Climate change is likely to increase the occurrence of climatic extremes of drought and heat, provoking large-scale tree mortality episodes. Mortality episodes have been observed in a wide range of forest types globally and in Australia (including river redgum, Cunningham et al. 2007; savanna, Fensham et al. 2009; jarrah, Matusick et al. 2013). However, not all vegetation types are equally at risk, because the likely severity of future droughts is variable across the landscape, and because sensitivity to drought varies among species. In this project, we aim to identify regions of NSW where future tree mortality risk is high. We are using physiological and ecological approaches to identify the drought tolerance of key habitat-structuring species and using future climate scenarios to work out where these tolerances might be exceeded. Ultimately we aim to develop maps of mortality risk that can help inform land management in NSW.
Turning water into carbon: a synthesis of plant water-use efficiency from leaf to globe (2012 – 2014) ARC Discovery project; CIs Belinda Medlyn, Remko Duursma, Colin Prentice, Almut Arneth. Post-doc Dr Yan-Shih Lin
Plant water use efficiency is the amount of carbon gained per unit water transpired, is a fundamental determinant of ecosystem function. Controlled by stomatal behaviour, it governs plant productivity, hydrology, and vegetation distribution. It has been very frequently measured, but there was little understanding of how it varies, due to a lack of theory to tie the observations together. We developed a new theory for water use efficiency and put together global data sets across a wide range of scales to develop a new, broad understanding of how water use efficiency varies.
Elevated CO2 effects on vegetation: repairing the disconnect between experiments and models (2010 – 2013) ARC Discovery Project; CIs Belinda Medlyn, Michelle Leishman, Sune Linder, Rich Norby, Ram Oren. Post-doc Dr Martin De Kauwe.
Atmospheric CO2 is currently increasing at an unprecedented rate, which has important consequences for vegetation: plants can photosynthesise faster and shut their stomata to conserve water. Ecosystem models need to take these effects into account, but to do so they need to be solidly based on experimental evidence. Our goal in this project was to synthesise data from a wide range of high-CO2 experiments in ways that could be used to inform models. We contributed to a model comparison of the Duke and ORNL forest FACE experiments that led to a solid understanding of which CO2 effects models capture and which they don’t. We’re now applying similar methods to the new EucFACE experiment at UWS. We also tested and developed models for the effects of atmospheric CO2 on stomatal behaviour, the interactions with drought and temperature, the response of different species types, and the implications for competition among species.