EFFECTS OF BURNING ON NUTRIENT BALANCE IN AN AREA OF GORSE (ULEX-EUROPAEUS L.) SCRUB

Wildfires affect nutrient balance as a result of combustion of biomass , increased surface and subsurface runoff and increased soil erosion. In the present study, nutrient inputs and outputs to burnt and unburnt Ulex scrub plots were monitored over a 2-year period. During burning, between 50 and 75% of the nutrients contained in above-ground plant t issues were directly lost due to volatilization and upward movement of particulates to the atmosphere. Only small amounts (less than 3% for all. elements) were deposited at the soil surface as ash. During the f irst rains after burning, N, P and K losses were largely due to sedime nt transport in surface runoff, while Ca and Mg losses were roughly eq ually distributed between sediment losses and soluble-form losses (in surface runoff and subsurface flow) and Na losses were largely in solu ble form. Post-burning nutrient inputs to the soil in throughfall were lower than in the control plots for N and K; in the case of the remai ning elements (P, Ca, Mg and Na), inputs to the burnt plots and contro l plots differed little. In general, burning led to clear net losses o f nutrients; annual losses were approximately 2.5-3.5 g m(-2) in the c ase of N and approximately 6.5-9.0 g m(-2) in the case of K. In the un burnt plots, by contrast, outputs were approximately equal to inputs. (C) 1997 Elsevier Science B.V.