Impacts of prescribed burning on soil greenhouse gas fluxes in a suburban native forest of south-eastern Queensland, Australia.

Prescribed burning is a forest management practice that is widely used in Australia to reduce the risk of damaging wildfires. It can affect both carbon (C) and nitrogen (N) cycling in the forest and thereby influence the soil-atmosphere exchange of major greenhouse gases, i.e. carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). To quantify the impact of a prescribed burning (conducted on 27 May 2014) on greenhouse gas exchange and the potential controlling mechanisms, we carried out a series of field measurements before (August 2013) and after (August 2014 and November 2014) the fire. Gas exchange rates were determined at 4 replicate sites which were burned during the combustion and another 4 adjacent unburned sites located in green islands, using a set of static chambers. Surface soil properties including temperature, pH, moisture, soil C and N pools were also determined either by in situ measurement or by analysing surface 10 cm soil samples. All of the chamber measurements indicated a net sink of atmospheric CH₄, with mean CH₄ uptake ranging from 1.15 to 1.99 mg m^-2 day^-1. The burning significantly enhanced CH₄ uptake as indicated by the significant higher CH₄ uptake rates at the burned sites measured in August 2014. While within the next 3 months the CH₄ uptake rate was recovered to pre-burning levels. Mean CO₂ emission from forest soils ranged from 2721.76 to 7113.49 mg m^-2 day^-1. The effect of prescribed burning on CO₂ emission was limited within the first 3 months, as no significant difference was observed between the burned and the adjacent unburned sites in both August and November 2014. The temporal dynamics of the CO₂ emission presented more seasonal variations, rather than burning effects. The N₂O emission at the studied sites was quite low, and no significant impact of burning was observed. The changes in understory plants and litter layers, surface soil temperature, C and N substrate availability and microbial activities, resulting from the burning, were the factors that controlled the greenhouse gas exchanges. Our results suggested that the low intensity prescribed burning would decrease soil CO₂ emission and increase CH₄ uptake, however, this effect would be present within a relative short period. Only slight changes in the surface soil during the combustion and very limited damages in the mineral soils supported the quick recovery of the greenhouse gas exchange rates. [ABSTRACT FROM AUTHOR]