Since 1984, an ongoing joint project of the International Institute for Tropical Agriculture (IITA) and the United Nations University has been studying the effects of deforestation on the soils, hydrology, microclimates and biotic environments of land-use systems abutting tropical forest. The project is being conducted on cleared plots and adjacent high rainforest land 75 km southeast of Benin City, Nigeria. Eight types of land-use systems are being studied, including:
(1) traditionally cleared
and farmed plots supporting yam, tomato and melon mixtures,
(2) alley cropping of Gliricidia sepium with rice/cowpea crops,
(3) improved forestry,
(4) oil palm with maize/cowpea crops,
(5) coconut pastures,
(7) cassava, and
(8) forested control.
Plots #2-7 were cleared using a shear blade mounted on a bulldozer. As expected, clearing forest exerts a considerable effect on the microclimate. Evaporation rates were 10-12 times greater in the cleared plots than in the control. The cleared plots also had higher radiation levels, lower minimum relative humidity and higher maximum air temperatures than the forested control. Within two years after planting, the microclimate under Cassia siamea forest in test plot #8 was similar to that under the natural forest. Bulk density of soil was highest in the mechanically cleared plots even two years after initial cutting. Steady-state infiltration rates were highest in the manually cleared, traditionally farmed plots (304 cm/h) and lowest in the mechanically cleared plots (47 cm/h). The surface runoff rate, measured under forest and oil palm plots, averaged 1.34 % of the rainfall under forest and 2.20 % of the rainfall under oil palm. Related IITA studies using legumes (Psophorcarpus, Centrosema and Stizolobium) as live or in situ mulches have shown promising results in reducing this type of runoff.