Site quality assessment and allometric models for tree species in the Oban Forest, Nigeria

The suitability of site form (SF) methods for evaluating site quality was investigated. Systematic sampling techniques were used for plot location in four sites (Aking, Ekang, Erokut, and Ekuri) within the Oban Forest of Nigeria. Four 2-km-long transects/sites were sampled, totaling 16 transects. Five 0.25-ha plots were alternately laid along each transect, making 80 plots. All trees with diameter at breast height (DBH) >= 10 cm were measured for height and diameter at the merchantable limit, middle, and base. Soil samples were collected at 0-15 and 15-30 cm depths in each plot, then analyzed using standard laboratory procedures. Site forms were computed using an index diameter of 25 cm. Data were analyzed using descriptive statistics, correlation analyses, and regression models. Ekuri had the highest stand density (173.0 +/- 51.0 stems/ha), Erokut had the lowest (143.0 +/- 39.0 stems/ha). Ekang had the highest stem volume (3,847.14 +/- 2.16 m(3)/ha), while Erokut had the lowest (2,127.71 +/- 1,382 m3/ha). The most productive site was Ekang (SF = 26.52 m), while Erokut was the least productive site (SF = 21.70 m). Stem volume (SV) has significantly positive correlations with soil organic matter, calcium, and silt. The best height-diameter model was logarithmic (R-2 = .51; RMSE = 4.462). The most suitable SV model was polynomial (R-2 = .85; RMSE = 2.207).