Variability of aboveground and belowground carbon stocks in Florida flatwoods ecosystems undergoing restoration and management

Background/Question/Methods
It has been well documented that terrestrial ecosystems have a great potential to store and sequester carbon. Therefore, a former ranchland at the Disney Wilderness Preserve, Central Florida, USA is being restored to native ecosystems and managed to preserve biodiversity and increase carbon storage. This study quantified the carbon stocks within the aboveground biomass, litter, belowground biomass, and top 90 cm of soil in five ecosystems at the Disney Wilderness Preserve, all of which are managed with prescribed fire every two to three years. These carbon stocks were compared in ecosystems in different stages of restoration: bahia grass pasture, pasture in restoration for longleaf pine flatwoods, and restored longleaf pine flatwoods. The carbon stocks were also compared among three restored flatwoods communities: longleaf pine flatwoods, slash pine flatwoods, and scrubby flatwoods. To determine the effects of prescribed fire management, carbon stocks were estimated and compared in recently burned (4 months prior) areas and areas burned two to three years prior, in all ecosystems. Soil carbon properties were assessed using ¹³C isotope analysis.

Results/Conclusions
Aboveground biomass and litter carbon stocks increased with higher stage of restoration, and were significantly reduced by fire management. Belowground biomass carbon stocks also increased with higher stage of restoration. Soil carbon stock did not differ significantly in different stages of restoration or with different times since fire, but differed significantly between the flatwoods communities. In un-restored pasture and pasture in restoration sites, the soil was increasingly depleted in ¹³C with increasing soil depth. This pattern indicated that carbon in the upper, more labile soil carbon pool had been derived from current C4 pasture or native grasses, while carbon in the deeper, more stable carbon pool is a legacy of the historical C3 forest vegetation that existed prior to conversion to pasture. Additionally, a pattern of less depletion in ¹³C with increasing time since deforestation was noted, indicating an increasing loss of historic forest carbon with increasing pasture age. The isotopic composition of the soil profile in the restored longleaf pine flatwoods may serve as a reference value for soil profiles of the restoration sites. Currently at this site, the five ecosystems store approximately 400,000 Mg C, and this value could increase by approximately 8300 Mg C once the pastures are restored to longleaf pine flatwoods.