Crop-based agroforestry systems in the buffers of protected areas: Implications for tree species conservation in Okomu National Park, Nigeria

Abstract

Woody species inventory was carried out in the traditional agroforestry around Okomu National Park (ONP), Nigeria, to ascertain the conservation of trees/shrubs in the farming systems. Systematic line transects were employed in the laying of Temporary Sample Plots (TSPs) in the existing compartments of ONP forest ecosystem. Two temporary sample plots of 25m x 25m (0.0625ha) in dimension were established in alternate positions along transect at 100m interval, amounting to four (4) temporary sample plots per range and a total of sixteen (16) TSPs within the national park. Total enumeration of live woody species was carried out in each sample plot. Three predominant farming systems were selected from buffer zone and boundary communities. Four (4) farms were purposively selected from each of the farming systems and used as sample plots. All live woody species present on each farm were enumerated and recorded, and diversity indices used to analyze species density and diversity. The density of the tree species identified in the study area include 519, 35, 174 and 80 (ha-1) for ONP, Cassava, Cocoa and Plantain land uses respectively. While diversity indices ONP, Cassava, Cocoa and Plantain land uses were: Shannon’s diversity index of (3.431, 1.868, 2.168 and 2.284); Species evenness (0.711, 0.711 0.537 and 0.733); Families Annonaceae, Meliaceae were the richest families identified in ONP while families Moraceae, Mimosoideae were common to the three agroforestry land uses. The analysis of variance of the diversity indices revealed that the biodiversity of the three farming systems differed significantly (P ≤ 0.05)from ONP. However, all land uses surveyed showed no significant difference in species evenness. The species diversity indicates that traditional farming systems can be effective biodiversity conservation tools in the edges of protected forests and consequently provide environmental sustainability.