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

Abstract

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 CO2. 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.