School of BEES - Research: Carbon Exchange Modelling

CURRENT RESEARCH BY PROFESSOR ROSS McMURTRIE

Modelling of carbon-exchange and productivity of forests in water- and nutrient-limited environments

Application of models to carbon-exchange data:
(Publications: 56)

Over the last decade a new type of canopy data has become available that provides a tremendous opportunity to critically improve simulation models. The data derive from a technique known as eddy covariance that measures fine-timescale carbon and water fluxes between vegetation and the atmosphere. We have been working on eddy-covariance data from several sites: forests in Australia (Tumbarumba), France, Scotland, Sweden, USA, and savanna in Australia and South Africa. Belinda has applied the detailed model of forest carbon exchange (MAESTRA) to three coniferous European forests with contrasting net carbon exchange to pinpoint reasons for the differences among sites (56, 100). MAESTRA was tested against eddy-covariance data and found to successfully simulate carbon exchange by each forest. Simulations were then run to compare carbon balance among the 3 sites. The most important factor was the differences in respiration rates, particularly soil respiration rates, among sites. Climate was also a very important factor, with differences in incident light affecting gross primary production GPP and differences in temperature affecting both GPP and ecosystem respiration.

Modelling productivity of water- and nutrient-limited forests:
(Publications: 9, 10, 11, 13, 14, 15, 17, 22, 23, 28, 32, 58, 59, 67, 76, 77, 78, 79, 92)

Australia is the driest of all continents and also has the lowest primary productivity (excepting Antarctica). The overall aim of this ongoing research, in collaboration with Professors Mark Adams (University of Western Australia) and Derek Eamus (Univ. Technology, Sydney) is to explain mechanisms linking these observations. The objectives of this research are: (a) to establish relationships between site water status and net primary productivity (NPP) in four woody ecosystems; (b) to establish mechanisms by which site water status influences NPP; (c) to determine the relative importance of these mechanisms; and (d) to incorporate this understanding into the G'DAY ecosystem model. Mechanisms underlying the relationship between site water status and productivity include: (1) stomatal response to vapour-pressure deficit; (2) differences in leaf-scale attributes; (3) altered respiration rate; (4) hydraulic limitations and (5) differences in leaf area index. G'DAY has been applied to E. globulus plantations in south-western Australia in collaboration with CSIRO with contrasting mean annual rainfall, water-holding capacities and fertilities (Dave & Ross, 58).

CURRENT RESEARCH DIRECTIONS

Our current work on the above topics includes:

Applying models to gas exchange and hourly eddy-covariance data from an E. delegatensis stand at Tumbarumba NSW (Belinda & Dave).
Applying G'DAY to daily time-step eddy-covariance data for various forest and savanna sites. The savanna system is important in Australia because of its ecological sensitivity and vastness (occupying 25% of Australia's land area), and because massive vegetation change is taking place across much of the Australian savanna (Ross).
Participation in a new Swedish project where effects of enhanced N deposition and fertilisation on boreal pine forests are to be measured using eddy-covariance methodology (Ross, in collaboration with Sune Linder).
Modelling of growth of plantation eucalypts in north-eastern NSW (Ross & Dave, in collaboration with Dr Dane Thomas, State Forests of NSW). SF-NSW is embarking on a major expansion of its eucalypt plantation estate in N-E NSW with extensive new plantings on ex-agricultural land of marginal quality. This work aims to develop a system for selecting the best species to plant at specific sites (based on climate-site data), and for identifying best management practices for plantations.
Applying models to uneven-aged native black-butt forest stands in N-E NSW (David Dore).
According to a recent global synthesis of NPP data, Australian forests have lower NPP than forests elsewhere in the world with the same rainfall. This raises the question of why Australian forests have relatively low water-use efficiency. Can the difference be explained from plant physiological mechanisms? Or, is it due to harsher weather conditions or infertility of Australian soils? If low fertility is the cause, then can that be explained from biogeochemistry, or fire frequency?