An indicative estimate of carbon stocks on Victoria's publicly managed land using the FullCAM carbon accounting model

The Victorian Department of Sustainability and Environment (DSE) is responsible for managing public land in Victoria. The land comprises mostly national park and state forest tenures but also includes a range of other Crown land tenures. The broad goal of this study was to provide an event-driven set of carbon accounts for Victoria's publicly managed land. An event-based model increases the understanding of fluxes in carbon stocks and informs the policy development process in areas relating to managing carbon as an asset. The study aims to discuss the method and its imperfections in addition to investigating the results from running the model. Variation in carbon stocks across the state is virtually unknown, with most past investigations occurring within the actively harvested, productive forest. This paper constitutes the first attempt at modelling carbon on all publicly managed land in Victoria. The study area was stratified on the basis of historical event data that are known to influence carbon stocks, such as fire and harvesting activities and geographic region. Large volumes of historical event data were simplified and aggregated to allow modelling and used to determine the stock trajectories for each stratum. The input resided in a geographic information system (GIS), and a database system was developed to pass data to and from the carbon accounting model, FullCAM, where carbon stocks were calculated. Simulations showed that carbon stocks were most heavily influenced by wildfire events, with more than 16 million t of carbon, or 2% of the total stock of 750 million t of carbon (2750 million t CO2), emitted by fires during the period from 2000 to 2009. Furthermore, the total carbon stocks of Victoria are highly correlated with large-extent wildfire events, yet even so the effect is largely transient even if corresponding emissions are significant. Events such as harvesting, wildfires and prescribed burns are major causes of change in carbon stocks on Victoria's publicly managed land. Of these events, the direct effect of harvesting is greater in reducing carbon stocks at particular locations than either wildfire or prescribed burning, yet the relative effect of wildfires is greater due to the spatial extent of these events. Prescribed burning has very little effect on carbon stocks in the FullCAM model, due to the patchy nature of these events and generally low intensity of prescribed burning operations. The forested lands are resilient to effects of harvesting and fire as carbon stocks were found to return to pre-disturbance levels, with recovery of the debris pool being fastest. The soil carbon pool is relatively stable, whilst the live vegetation carbon pool is the most dynamic and heavily influenced by events.