EFFECTS OF TIME-SINCE-FIRE ON SOIL NUTRIENT DYNAMICS IN FLORIDA SCRUBBY FLATWOODS

Differences in the volatilization temperatures and sources of inputs of nitrogen (N) and phosphorus (P) suggest that fire will decrease N relative to P over the short term and that N will increase relative to P over the long term after fire. In Florida scrubby flatwoods—a pyrogenic ecosystem that occurs on sandy nutrient-poor soils—we tested the hypotheses that N availability increases with time-since-fire, that P availability decreases with time-since-fire, and that the ratio of available N to P increases with time-since-fire. We measured nutrient availability and soil characteristics in scrubby flatwoods sites along a time-since-fire chronosequence (1, 4, 6, 8, and 10 yr since fire). Resin-exchangeable and K2SO4-extractable N, soil N and C pools, potential net N mineralization, chloroform-labile microbial N, resin-exchangeable PO43-, and resin-exchangeable N:P ratios did not differ significantly with time-since-fire. Turnover of organic matter likely controls nutrient availability in scrubby flatwoods; and low organic matter in sandy scrubby flatwoods soils, coupled with sequestration of nutrients in plant biomass, appears to limit accumulation of soil N with time-since-fire. In contrast to many other fire-influenced ecosystems, we did not detect a long-term effect of fire on nutrient availability in scrubby flatwoods.