Biophysical controls of carbon exchange in old growth Mountain Ash stands

Long-term measurements of CO2, H2O and energy fluxes over a range of terrestrial ecosystem types and maturity are necessary in determining the regional and global carbon budgets. Previous studies from temperate forests have generally shown that the net uptake of carbon (NEE) of ecosystems decreases with stand age, and in old growth forests carbon cycling has often been assumed to be in equilibrium. However, results from the Northern Hemisphere, using eddy covariance flux towers, indicate that old growth forests are a greater sink than first thought. Changes in stand structure, detritus matter and microclimate between young and old growth forests greatly contribute to the variation in the net fluxes of CO2 and H2O. The role of old growth temperate forests in Australia is uncertain and may function remarkably different to their deciduous counterparts in the Northern Hemisphere. An undisturbed old growth, Mountain Ash (Eucalyptus regnans) ecosystem, located in the Central Highlands of Victoria (Australia) has been selected as a permanent study site to investigate carbon and water budgets over diurnal, seasonal and annual cycles. Mountain Ash trees are the world's tallest angiosperms (flowering plant), and fully developed trees can reach heights of more than 100 metres. Mountain Ash forests also occupy a large proportion of Victoria's catchments, making them a crucial resource for the sustainable management and quality of Melbourne's drinking water. This study uses the Eddy Covariance method, which will measure the carbon, water, energy fluxes. The site has been running since August 2005 and we present 18 months of preliminary results from the site. The central theme of this study is to investigate the climatic and biophysical factors that control carbon, water and energy cycles over a range of time scales. Ultimately, this approach will allow us to better understand how these uniquely Australian ecosystems may respond to global climate change.