Effects of fire on nutrient availability in Florida scrub

Fire has profound effects on ecosystem nutrient dynamics. Fundamental differences in the biogeochemical cycles of nitrogen (N) and phosphorus (P) suggest that fire will have differential effects on the availability of these nutrients. When plant material is consumed by fire, N may be volatilized and lost from the ecosystem, whereas P will be returned to the ecosystem in ash. Florida scrub ecosystems are fire-adapted and occur on sandy, nutrient poor soils. Although fire is an important disturbance in Florida scrub, little is known about the effects of fire on the availability of N and P. We measured soil nutrient availability in scrubby flatwood sites along a fire chronosequence (1, 4, 6, 8, 10, and 13 years since fire). Ion exchangeable NH₄⁺ and net N mineralization were lower in recently burned and long unburned sites and higher in sites with intermediate times since fire. By contrast, ion exchangeable PO₄^3- was highest in the most recently burned and the longest unburned sites. These results suggest that fire shifts the relative availability of N versus P, and thus, that nutrient limitation may change with time since fire.