Effects of fire on soil CO2 - Implications for karst processes

Wednesday, 17 December 2014
Katie Coleborn1, Andrew Spate2, Mark Tozer3, Pauline C Treble4, Martin S Andersen5, Ian J Fairchild6, Andrew Baker3, Stephen Meehan3 and Andy Baker1, (1)University of New South Wales, Sydney, NSW, Australia, (2)Optimal Karst Management: Cave and karst consultancy, Sandy Bay, Australia, (3)New South Wales Office of Environment and Heritage, Sydney, Australia, (4)Australian Nuclear Science and Technology Organisation, Institute for Environmental Research, Lucas Heights, NSW, Australia, (5)University of New South Wales, Sydney, Australia, (6)University of Birmingham, Birmingham, United Kingdom
Fire reduces soil CO2 concentration by destroying vegetation and soil dwelling microbial communities thus reducing both heterotrophic and autotrophic contributions to soil respiration. While reductions in microbial respiration are short-lived, root respiration can take longer to recover, depending on the dominant growth forms (e.g. trees vs herbs) and modes of post-fire recovery (e.g. resprouting vs seedling establishment). This study aimed to quantify whether soil CO2 concentration was reduced ~5 years and ~10 years after a fire in a subalpine karst environment in south-eastern Australia and to consider the implications for karst dissolution processes and speleothem growth rate. Paired sites with burnt and unburnt soil were compared with regards to CO2 concentrations, soil moisture and soil temperature. Samples were taken from a grassland site and woodland site burnt ~5 years ago and a woodland site burnt ~10 years ago. The results showed that soil respiration was depressed in burnt sites relative to the unburnt pair in both the grassland and woodland sites after ~5 years; however, after ~10 years there was no significant difference between the burnt and control woodland sites. This indicates that soil CO2 concentration takes between 5-10 years to return to pre-fire levels in subalpine environments in south-eastern Australia. In a karst environment, this long-term reduction in soil CO2 concentration caused by fire is likely to cause a decreased stalagmite growth that could be incorrectly attributed to multiannual climatic drying, such as the El Nino Southern Oscillation, when reconstructing past environmental change from stalagmite records.