The Effects of Fire and Termites on a Zambian Woodland Soil

Abstract

Grass-burning experiments in natural standing woodland in Zambia were maintained continuously by the then Northern Rhodesia Forest Department from 1933 onwards, the treatments including both late and early burning and complete protection. The effect which these treatments had on the top 15 cm of soil after 23 yr is discussed. The soils are of very low organic content and extremely low base saturation. The pH, exchangeable Ca and phosphate status were markedly improved by the burning treatments, when compared with the effect of protection, and particularly by late burning. These effects are consistent with the composition of wood ash in this region. A notable result was the complete lack of effect of protection on the content of N and organic matter. The lack of effect on organic matter is due to the disposal of litter by large populations both of humus-feeding and of wood- and litter-feeding termites. Small Cubitermes-type mounds of the humus-feeding class had 3-4 times the organic C concentration of surface soils and a marked increase in exchangeable bases with high base saturation. Large mounds of Macrotermitinae of the wood-feeding class showed corresponding increases in organic C over normal subsoil and still greater increase in the bases. It is suggested that fire and termites exert complementary effects on the base status of the soil, the fires promoting the return of bases brought down in litter from the woodland canopy, while the termites deplete this return by consuming unburnt litter, the derived bases gradually becoming concentrated in the large termite mounds. In either case, the organic content of the soil is kept at a very low level.