Changing Australian vegetation from 1788 to 1988: Effects of CO₂ and land-use change

We present a tractable and transparent approach (the TMSC model) to estimating the total stock of carbon (roots, stems and leaves) in living vegetation (C _living), from gross primary productivity (GPP) estimates. The TMSC model utilises the TMS scheme of canopy functional types and a generic allometric scheme to derive these estimates. Model estimates are presented for the Australian continent under the following three vegetation?[CO₂] scenarios: the present (1988) vegetation and a hypothetical natural (1988) vegetation cover with atmospheric CO₂ concentration ([CO₂]) of 350 μmol mol^-1 (pveg350 and nveg350), and the natural vegetation (1788) having [CO₂] of 280 μmol mol^-1 (nveg280). The change between the nveg280 and pveg350 scenarios represents the combined effects of changes in land use and CO ₂. The change resulting from CO₂ alone is the difference between the nveg280 and nveg350 scenarios. The estimated C _living for the continent is 21 Gt for pveg350, 23 Gt for nveg350 and 10 Gt for nveg280. This translates to an averaged rate of increase in C _living (CSI) of about 50 Tg C year^-1 over the last 200 years for the continent. Where wooded areas have been extensively cleared for agriculture, the CSI is negative (down to -4 g C m^-2 year^-1). Elsewhere, the CSI over the last 200 years ranges from ∼55 g C m^-2 year^-1 in the tropical and subtropical forests to ∼0 g C m^-2 year^-1 in the most arid regions.