Impact of Slash Burning on Nutrients in Industrial Plantations: A Conceptual Model for the Tsitsikamma, South Africa.

SYNOPSIS

Slash treatment experiments were conducted after clearfelling of Pinus pinaster in the Tsitsikamma Forest Region, South Africa, to determine the effect of burning on pH, N and P budgets. pH(H₂O) increased from an average of 4,49 to 4,78 and P-budgets in the topsoil increased by 60 % at the expense of a P-budget loss of 25 % in partly-consumed H (humus) layers, and a total loss of P in L and F-layers, which was completety consumed by the fire. N concentrations in the topsoil after burning ranged from 607 to 2 129 mg/kg. A volatilisation of 60 % of total N in forest floor layers, and 10 to 15 % of the total N-budget, is predicted.

The increase in P and decrease in N budgets will act favourably to reduce high NP ratios, which will reduce the occurrence of Pinus radiata growth disorders experienced. The increase in P levels as a result of burning is inadequate for normal tree growth requirements, and fertiliser applications will still be needed to address the critical P shortages in the Tsitsikamma.