Tree Slenderness Coefficient and Percent Canopy Cover in Oban Group Forest, Nigeria

Abstract

Oban Forest health was assessed using tree slenderness coefficient (SC) and percent canopy cover as indicators. Systematic sampling technique was adopted for plot locations in Aking, Ekang, Erokut and Ekuri sites within the forest. Four transects of 2 km-long situated 600 m apart were established in each site. Five 0.25ha-plot were then alternately laid along each transect at 400 m intervals. A total of 20 plots per site, and 80 plots in all were used. Tree heights, Dbh and crown diameter were measured on trees with Dbh≥10cm to compute SC and percent canopy cover (%CC). Trees were classified based on their SC as high (SC>80), moderate (SC: 70-80 and low (SC<70). Data were analyzed using descriptive statistics and correlation analysis. There were 36, 49 and 67 trees/ha with high, moderate and low SC, respectively for the pooled data with 56.5% CC. On site basis, Aking had 145 trees/ha, and of these, 44, 45 and 56 trees/ha had high, moderate and low SC, respectively. Ekang had 147 trees/ha, and of these, there were 45, 50 and 52 trees/ha with high, moderate and low SC, respectively.  Erokut had the least 143 trees/ha, and of these, 37, 50 and 56 trees/ha were with high, moderate and low SC, respectively with 49.95% CC. Ekuri had the highest 173 trees/ha, and of these, 62, 43 and 68 trees/ha had high, moderate and low SC, respectively with 59.8% CC. There were negative correlations between SC and other tree growth parameters except tree height (r = 0.07). About 24% of the trees had high SC, which implies high susceptibility to wind-induced damage, with highest trees/ha in this category found in Ekuri site due to high stand density. This may cause competitions among trees, thereby limiting trees development. Hence, appropriate silvicultural treatment such as low-impact logging is recommended.

Keywords: Stand stability, slenderness ratio, crown dimension, susceptibility, wind-throw