Fire Effects on Soil Biogeochemistry in Florida Scrubby Flatwoods

Fire is a major factor in the ecosystem dynamics of upland Florida habitats. Fire impacts have been well studied in terms of plant community responses, but the effects of fire on soil characteristics and post-fire plant-microbial interactions in these systems remain poorly documented. We investigated the effect of fire intensity and pre-fire vegetation on soil biogeochemistry in Florida scrubby flatwoods. We measured vegetation structure in 30 plots of 1/4 m radius before a prescribed burn. Fire duration and temperatures were recorded in each plot. Soil samples taken immediately preceding and 2 w after the burn were analyzed for organic matter, inorganic N, available P and K, N mineralization rates, and potential nitrification rates. All nutrients and N mineralization rates significantly increased after fire. N and P increases were positively correlated with both fire intensity and vegetation. N mineralization was most strongly correlated with changes in available soil P, suggesting P stimulated N mineralization. These results contrast with the few other studies in Florida scrub, which found no effect of fire on soil nutrients. We suggest that taking measurements within a few weeks of burn and using a shallow sampling depth is necessary to document the nutrient pulse in these sandy, nutrient poor systems, and we recommend more research into fire's effect on the soil microbial community. Fire's impact on nutrients and nutrient turnover rates could have important repercussions on post-fire vegetation regrowth. Understanding the effects of fires on soils is therefore critical to developing fire management protocols.