Above-ground nutrient dynamics of Caribbean Pine (Pinus caribaea) plantation ecosystems

Growth, biomass and nutrient accumulation by 14-year-old stands of Caribbean pine (Pious caribaea Morelet var. hondurensis Barr. and Golf.) on three subhumid savanna sites in Nigeria were investigated. Soil organic carbon, total N, extractable P and exchangeable K, Ca and Mg showed significant decline in the upper 10 cm of the mineral soil as a result of reafforestation with the pine.Estimates of the mean residence time of organic matter and nutrients in the litter layer of the ecosystems were 2 to 4 years thus indicating a slower rate of litter decomposition compared to litter of mixed natural savanna vegetation and broad-leaved plantations in which the residence time of organic matter rarely exceeds 6 months. Nutrient inventory in the different compartments of the pine ecosystem showed that a sizeable proportion of P and K was held in the tree biomass. Nutrient budget analysis showed that total biomass removal in above-ground tree harvest could lead to problem of P and K nutrition in future rotations on some sites. Estimates of nutrient fluxes and their relative contributions to tree nutrition were made. It was concluded based on the relative contributions of the fluxes that the soil remains the dominant source of the nutrients taken up by the tree and consequently tree nutrition as well as tree growth were soil fertility-dependent. Sites with low inherent nutrient quality were considered to be at a risk of nutrient depletion.