Litter Fall, Mineral Turnover and Litter Accumulation in Pinus caribaea L. Stands at Ibadan, Nigeria

Abstract

Litter fall was measured at approximately fortnightly intervals during a three-year peroid in adjacent stands of thinned and unthinned Pinus caribaea L. of the same age. Mean litter fall was 5988 ? (SE)647 and 5767 ? (SE) 308 kg/ha. yr in the thinned and unthinned stands, respectively. These values are similar to estimates of leaf litter fall obtained in mixed deciduous native forests in the same locality, but lower than values recorded for the wetter, humid, tropical forests. The mean annual returns of nutrients from the litter of both stands are similar and amount to an average of 26.2, 0.6, 14.0, 34.5 and 10.8 kg/ha for nitrogen, phosphorus, potassium, calcium, and magnesium, respectively. Compared to broad-leaved species, the return of nitrogen and phosphorus is very low. It is suggested that these elements may be limiting growth of the trees in the plantation. Measurements of pine-litter changes over a three-year period indicate that the litter builds up under Pinus caribaea L. as in the case of pine litter in higher latitudes. The time for the mineralization of one-year litter fall was estimated at 3.6 years as against the short period of 2 to 7 months in which litter of angiospermous species decompose in the area. LITTER FALL CONSTITUTES the major pathway in the biogeochemical cycle of terrestrial ecosystems. In the lowland tropics, it has been shown that a large proportion of the annual litter fall (especially the leaf litter) is decomposed within the year, usually between 2 to 5 months (Nye 1961, Madge 1965, Hopkins 1966, John 1973, Egunjobi 1974), thus releasing minerals to be reabsorbed by the plants or to be lost to the ecosystem by leaching and run-off. However, these studies have been conducted in areas dominated by broad-leaved, angiospermous species. Pines are not natives to West Africa, and very little is known about the fate of pine litter when grown in the lowland humid tropics. Preliminary investigations (Egunjobi and Fasehun 1972), however, indicate that pine litter may not mineralize as fast as litter of broad-leaved species, thus accumulating on the soil surface as in higher latitudes. This paper gives an account of litter fall, mineral content of the litter, and litter accumulation in a Pinus caribaea stand.