think climate. think change.
Department of Climate Change
Ben Harms and Ram Dalal, Department of Natural Resources and Mines, Brisbane, February 2003
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The amount of organic carbon in soil at a given time is a function of carbon input and carbon decomposition rates, as influenced by soil temperature and soil moisture (rainfall and evaporation), and soil type. Land clearing disrupts this balance by removing vegetation, thereby reducing the carbon dioxide (CO2) sink and transfer of carbon to soil as well as by increasing CO2 emissions from dead biomass and soil carbon. Therefore, land clearing invariably leads to changes in soil carbon, which need to be accounted for in modelling total greenhouse gas emissions. As soil organic matter is the main supplier of soil nitrogen, changes in soil carbon are likely to be associated with similar changes in soil nitrogen.
This report completes a consultancy agreement between the Department of Natural Resources and Mines (Queensland) and the Commonwealth of Australia (represented by the Australian Greenhouse Office) to investigate soil carbon and nitrogen stocks and fluxes following land clearing in Queensland since 1970. Following the recommendation of Webbnet Land Resource Services (1999), it was agreed to select and investigate approximately 50 paired sites from the main areas of recent tree clearing in Queensland.
This study reports on sampling conducted at 33 sites across central and southern Queensland, representing a total of 49 paired plots. Soil type characterisation (profile description and laboratory analysis) for each plot was used to establish the validity of selected cleared and uncleared pairs. However, due to the short-range spatial variation that often present in soil landscapes, paired site studies are inferior to long-term experiments where soil changes are measured at exactly the same location before and after land use change. Laboratory analysis indicates that ten of the 49 paired plots may be less than adequately matched in terms of clay percentage and/or cation exchange capacity.
