Tree structural and species diversities in Okwangwo Forest, Cross River State, Nigeria

Abstract

For sound forest management decisions, appraisal of flora species and forest structure is crucial for any meaningful conservation work. We assessed tree species distribution in Okwangwo Forest, Nigeria. Systematic sampling technique was adopted for plot selection. 24 transects, measuring 1000m long at 500 m intervals were laid. Four sample plots of 0.25 ha were located alternately at 250m intervals along each transect, making 96 plots (24 ha) in all. The diameters of all the trees with dbh .10 cm were measured. All measured trees were identified to species level. Data were analyzed using descriptive statistics such as means, frequencies, percentages and charts. Also, species relative densities and  richness were computed. Tree species were grouped into abundance classes. A total of 125 tree  species belonging to 36 families and 96 genera were recorded in the area with Margaleffs index of species richness of 2.2754. Most (99) of the tree species  encountered were threatened/endangered, 23 species were rare with only 3 tree species (Brachystegia eurycoma, Bailonella toxisperma and Ceiba pentandra)  being  abundant in the area. Frequent and occasional species were not encountered in the area. Leguminoseae  was the most represented family  with 14.84% (19  species) with Styraceae, Polygonaceae,  Papilionioideae, Sapindaceae, Connaraceae, Flacourtiaceae, Tiliaceae, Asparagaceae, Ochnaceae,  Bignoniaceae,  Mimosoideae, Piperaceae, Anisophyllaceae and Violaceae being the least with one species each. The mean basal area of 111.32 m²/ha recorded in the area was higher than the value suggested for a well-stocked and managed forest in Nigeria. There were more trees in the lower diameter classes than in the larger classes. The result of soil physical and chemical properties was also impressive with potential for site quality improvement going by the good stand structure.