Historical vegetation dynamics and the carbon cycle: current requirements and future challenges for quantifying carbon fluxes in Australian terrestrial ecosystems

Concern about the potentially dangerous effects of increased atmospheric concentrations of CO2 and other greenhouse gases on global climate has resulted in international agreement to stabilise atmospheric concentrations of these gases. Terrestrial vegetation plays a significant role in the global carbon cycle and management actions that increase carbon stocks in vegetation and soils could potentially offset CO2 emissions from use of fossil fuels. Inclusion of such actions in international climate agreements has been controversial. The Kyoto Protocol allowed for a limited set of vegetation 'sink' activities to be accounted toward greenhouse-gas mitigation targets in the first commitment period and rules regarding implementation of these activities have recently been agreed. Inclusion of carbon in vegetation sinks in the Kyoto Protocol has focused policy attention on the need for better understanding and monitoring of carbon dynamics in terrestrial ecosystems. Recent investment in remote sensing, modelling and accounting systems has improved capacity to assess and report on carbon fluxes in vegetation, particularly those associated with recent land-cover change from forest to non-forest and vice versa. Quantitative understanding of carbon dynamics across the broader vegetation estate remains limited. Future challenges for a comprehensive assessment of carbon cycling in vegetation include quantification of the effects of changes in vegetation structure from historical changes in fire and grazing regimes, the impact of human and natural wildfire and the area and growth of regrowth forest created by past clearing and timber harvesting. Different repotting processes will require separation of the effects of human-induced versus natural processes. These will require greater investment in vegetation monitoring systems that efficiently integrate remote sensing and field measurements.