Non-linear tree crown ratio models in International Institute of Tropical Agriculture Forest, Ibadan

Abstract

Assessment and monitoring of forest is a key tool for environmental purposes which are an integral part to sustainable management of the forest. Crown ratio is generally used to describe the ratio of the crown length to tree total height. The prediction of crown ratio is based on empirical models which aid in the development of accurate predictions for both individual and stand growth, as well as yield, which are useful tools for analyzing a variety of management and decisions making. However, no single model can effectively provide enough information for all stages of decision-making. As such, this study was aimed at the development of crown ratio for International Institute of Tropical Agriculture (IITA) Ibadan. Data used was collected from International Institute of Tropical Agriculture (IITA) Ibadan, Nigeria. Simple systematic line transects of four parallel transect of 200m apart were used for plot laying. Sixteen sample plots of 25m × 25m were laid for data collection, all tree with Diameter at Breast Height (dbh) ≥ 10cm were measured to determine No of stand per hectares (Ni/ha), Quadratic mean dbh per hectare (DQ/ha) and Volume per hectare (V/ha). The entire response variable for predicting tree crown ratio model was measured and computed (Crown Length - CL, Crown Diameter - CD, Tree Slenderness Coefficient - TSC, Tree Total Height - TH and Merchantable Height - MH). Data were analyzed using both descriptive and inferential statistic using non-linear regression packages on R software at α0.05. Comparison of models was done using RMSE, R², AIC and BIC. The stand comprises of 389 stem ha^-1. The DBH, TH, N/ha, DQ, TSC, V and CD values ranged from 10– 170cm, 7.7m – 38.1m, 96 – 704, 18.047 – 52.655cm, 22 – 225%, 0.003 – 24.676m³ and 3 – 13.7m, respectively. The selected model for crown ratio is the Modified exponential model: CR= -0.81745+exp^{(0.05451CL-0.0934THT)} (RMSE = 0.027, AIC = -1278.412, BIC = -1263.705 and R²= 0.906). The established crown ratio models have a substantial association with CL and THT, and may be successfully employed for crown ratio prediction investigations in IITA.