Developing diameter distribution models in Ukpon rainforest reserve of Cross River State, Nigeria

Abstract

The aim of this study is to provide the most appropriate model for tree distribution into diameter classes in Ukpon tropical rainforest reserve of Cross River State, Nigeria. Systematic line transect was used to lay sample plots. Two transects of 1500m in length with a distance of at least 500m between the two parallel transects were used for this study. Sample plots of 50m x 50m in size were laid in alternate along each transect at 100m interval and thus, summing up to 10 sample plots per 1500m transect and a total of 20 sample plots in the study area. A total of 1100 individual tree species spread across 65 species belonging to 21 different tree families were measured for diameter at breast height, diameters at the base, middle and top and tree total height. The mean diameter at breast height and total height of 28.8cm and 18.6m were obtained. Mean basal area of 50.29 m2 ha-1 was obtained with a mean volume of 271.249 m3 ha-1. Easy Fit software was used for Diameter Distribution models. Three diameter distribution models were developed and validated for the reserve. However, Dagum four parameters (4P) was the more flexible among the selected diameter models in the reserve. None of the selected model was significant; meaning that each of the three models is accurate and fit for diameter prediction is the reserve. The research has provided easy to use diameter distribution models for prescription of silvicultural treatment per time in the reserve in order to enhance effective and efficient management of the reserve.