The role of terresterial ecosystems in the global carbon cycle has raised considerable interest among researchers and policy makers. Exchange between atmosphere and vegetation involves large two-way fluxes, with fixation of CO 2 into biomass through photosynthesis approximetaly balanced by the release of CO2 through processes of decomposition and burning. It is estimated about 60 Pg 1 carbon is exchanged (in both directions) between terresterial ecosystems and the atmosphere every year, with a net terresterial uptake of 0.7 ± 1.0 Pg 1 C (Lasco, 2004). However, relative to the size of the atmospheric pool of CO 2 , land use change and forest conversion aresignificant source of CO 2 contributing to around 1.7 ± 0.6 Pg C year (Watson et al . 2000). In geological history the process ofCO 2 fixation has dominated over that of CO 2 release, contributing to the large reserves of ‘fossil fuels’. At the current rate of global fuel consumption and economic growth, it ispredicted that within 100 years global mean temperature will increase by 1.7 – 4.5ºC (Houghton et al ., 2001).