Changes in Prescribed Fire Frequency Alter Ecosystem Carbon Dynamics

Abstract

Changes in fire frequency from historical norms are becoming more frequent due to both changes in management and climate change factors. There is uncertainty about whether increasing fire frequency will lead to decreased carbon pools due to shorter inter-fire recovery periods, or increased carbon pools due to lowered fire intensity due to lighter fuel loads. Additionally, data are needed to determine whether plant and soil carbon pools respond similarly and whether ecosystem responses are consistent across environmental gradients that can affect fire intensity, such as soil moisture. We measured soil and vegetation carbon pools and fluxes at sites that had experienced different experimental burn treatments over the previous 8 years and across a range of soil moisture in a longleaf pine (Pinus palustris) ecosystem in North Carolina, USA. We found that increasing fire frequency, assessed by either the number of days since a previous fire or the number of fires a plot had experienced over the previous 8 years, significantly reduced carbon stocks in the litter pool and soil carbon pool and reduced the productivity of understory plants. Total carbon stocks also significantly declined, and there was a marginally significant shift away from soil carbon and toward tree carbon as being the dominant carbon pool in the system with increasing fire. None of the results showed any interaction with soil moisture, suggesting that in this landscape, fire effects are consistent across an important environmental gradient. Over the timeframe of this study, management that increases prescribed fire frequency appears to reduce carbon storage.