Stock Density and Fruit Yield of African Walnut in Tropical Lowland Rainforests of Southwest Nigeria

Abstract

Despite the high socio-economic potentials of African walnut, Plukenetia conophora Mull-Arg, there is a dearth of information on stock density and yield studies under different site conditions. Therefore, this study was carried out to investigate the stock density and fruit yields of P. conophora in three different habitats (i.e. less disturbed natural forest, recently disturbed natural forest and plantation forest) within Omo Forest Reserve (OFR) and Shasha Forest Reserve (SFR) of Nigeria. Stratified random sampling was used to carry out the inventory survey. Fruit yields were determined by collecting fruit falls through double sampling approach. Both descriptive and inferential statistics were used in analysing the data at p=0.05. Stock densities of P. conophora were 5.33+1.7 stands/ha, 14.67+2.05 stands/ha and 16.00+2.94 stands/ha in OFR, while they were 7.33+0.47 stands/ha, 14.67+1.25 stands/ha and 10.67+04.7 stands/ha in SFR for recently disturbed forest, less disturbed forest and plantation forest respectively. There were significant differences in number and distribution of species by forest types, but not between forest reserves. The mean yield of P. conophora was estimated at 7,800 kg/ha/yr for OFR and 6,534 kg/ha/yr for SFR. Yields from plantation area contributed more in OFR, while yields from less disturbed natural forest area were higher in SFR. Yields from recently disturbed natural forest were consistently lower in the two reserves. These results show that P. conophora thrives better in plantation and old re-growth forests. This information is pertinent towards improving the management of the species, increase its productivity and enhance benefits in a more sustainable manner to the rural populace.