BIOMASS AND NUTRIENT DISTRIBUTION IN STANDS OF PINUS-CARIBAEA L IN THE DRY FOREST ZONE OF NIGERIA

The standing crops of P. caribaea at Ibadan, Nigeria, aged 6, 8, 9 and 10 yr were estimated to weigh 82.2, 81.6, 157.8, and 207.0 .times. 103 kg/ha, respectively. These estimates are 3-6% higher when corrected for error resulting from the logarithmic transformation of variables. The lower standing crop of the 8 yr old pines was attributed to a high tree mortality in this group and the use of a different potting mixture for raising seedlings. During this period the live standing crop declined from 95-88% of the total standing crop biomass while the ground litter increased from a low figure of 3.7 .times. 103 kg/ha at 6 yr to 19.7 .times. 103 kg/ha at 10 yr. As the plantation matured there was a consistent decrease in the proportion of standing crop in the leaves and an increase in the proportion contained in the bole. The mean annual rate of dry-matter production estimated at 32.8 .times. 103 kg/ha compared favorably with that (36.1 .times. 103 kg/ha) recorded for the fast-growing P. radiata in New Zealand, while the N and P occurred in comparatively low concentrations in the foliage as compared to P. radiata from that country. The distribution of N, P, K, Ca and Mg in the 6 and 10 yr old stands showed that these nutrients increased in relation to increases in the standing crop. In the younger stand, the quantities of N, P, K, Ca and Mg were 278.9, 11.9, 137, 126.2 and 62.1 kg/ha, respectively, while the quantities increased to 598.3, 26.7, 375, 295.5 and 116 in the older stand. Between 20 and 30% of the N, P, Ca and Mg, and as much as 40% of K were contained in the foliage, 6-14% in the branches, 20-30% in the bole, and 18-20% in the roots. Clear-felling at 10 yr, leading to removal of bole alone, may result in substantial removal of plant nutrients from the ecosystem.