HYDROLOGICAL NUTRIENT FLUX IN ISOLATED EXOTIC STANDS OF MANGIFERA INDICA LINN: IMPLICATIONS FOR SUSTAINABLE RAINFOREST ECOSYSTEM MANAGEMENT IN SOUTH-SOUTHERN NIGERIA

Abstract

Nutrient flux by exotic tree species is becoming very relevant to the sustenance and productivity of rainforest environment. Apart from being a source of shade and fruits, the growing of exotic trees within rainforest environment helps to return nutrient elements back to the soil. This study applied scientific approach to investigate rainwash nutrient flux in isolated exotic stands of Mangifera indica in south-southern Nigeria. This is with a view to managing the degraded rainforest environment owing to the high relevance of trees to man. Through fall and stemflow, water samples were taken from 15 stands of M. indica and rainforest (control) for one year. Throughfall and water samples from open space (incident rainfall) were taken with funnel-type collectors; while samples from stemflow were collected by tying ¾ mm hose round the tree trunks. Samples collected were analysed in the laboratory using standard methods. From the stands of M. indica and control sites, annual throughfall volumes (%) were 88.6 and 84.2; while stemflow volumes (%) were 6.2 and 7.3 of the water samples from open space (4325mm). Nutrient elements released back to the soil via the rainwash sources varied. N, P, K, Ca., Mg. and Na. returned via throughfall from stands of M. indica were 3.43, 0.78, 9.5, 5.77, 2.17 and 0.81 kg/ha per year; the corresponding values for the control were 6.04, 0.58, 8.5, 4.46, 2.13 and 0.65 kg/ha/yr. While N, P, K, Ca., Mg. and Na. released to the soil via stemflow from stands of M. indica were 0.25, 0.04, 0.3, 0.42, 0.26 and 0.04 kg/ha per year; the corresponding values for the control were 0.47, 0.08, 0.7, 0.28, 0.55 and 0.14 kg/ha per year. Exotic trees release nutrients back to the soil under their stands. The nutrient elements released to the soil by exotic trees help to improve soil qualities within the rainforest ecosystem.