Effects of Fire on Nutrient Movement in a South Carolina Pine Forest

Abstract

The movement of major cations, nitrate, and phosphate was studied in burned and control areas of a South Carolina pine forest. Artificial leaching of litter showed that fire increased the solubility of cations by the following factors: Ca++, 20 °; Mg+?+, 10 x; Na+, 2.3 x; K+, 2.3 x. Natural leaching over a 1—mo period reduced the ion yield of burned litter by 80%—83% for divalent cations and 45%—63% for monovalent cations. Amounts of soluble nitrate and phosphate were identical in burned and unburned litter samples. Nitrate and phosphate were substantially higher in the first rainfall at the burned area after the burn, but not in subsequent rains. Collections of rainfall plus fallout from the burned area consistently contained about twice the amounts of cations present in similar collections from the unburned area. Runoff was low but contained greater amounts of cations in the burned area. Samples of superficial groundwater provide some evidence for changes in ionic balance due to burning. Biologically available N and P in the litter is apparently not increased directly by burning, but a rise in soluble nitrate and phosphate occurs some time after the burn and is probably due to increased microbial activity. Large amounts of N are probably volatilized and could exercise important effects on the productivity of systems remote from the burn if some biologically active compounds are included in the vapor. Although the upper soil layers are an efficient adsorption trap for cations, there is a potentially important movement of ions in runoff, in groundwater, or in the wind as particulate matter following a fire.