Assessment of growth variables and regression models for the tree volume prediction of <i>Azardirachta indica</i> (a. Juss) at Warwade plantation, Dutse, Jigawa state, Nigeria

Abstract

Savannah is well known with less diverse ecosystem. Tree growth dynamics is a major technique in quantifying the forest composition. However, there is need to determine community structure and model which is suitable for Azadiractha indica in arid land.Therefore, the experiment was carried out to assess the tree growth variables and regression models for tree volume prediction of Azadiractha indica in Warwade plantation. Four (4) plots of 25m x 25m were using random sampling technique at interval of 100m from each other. Tree growth variables such as: diameter at breast height (DBH), diameter at the base (Db) middle (Dm), top (Dt) and height were taken with aid of Spiegel relascope. Frequency of occurrence of all tree with diameter at breast height (DBH) ≥10cm were measured. Three regression models were developed which are exponential, Quadratic and Vapour pressure. A total of eighty-one (81) stems ha^-1 of the species were identified and counted. The tree growth variables measure showed that Azadiractha indica plantation had total volume of 14126.59m³ per ha^-1 and basal area was 339998.19m². The range of 61-70cm of diameter class had the highest number of terms per hectare (33.33%). The models developed showed that exponential model volume was found to be more suitable and good fit for tree volume prediction in the context of the data used. Therefore, exponential model generated in this study is recommended for volume prediction at Warwade Forest Reserve, Dutse, and Jigawa State.

Keywords: Growth Assessment, Regression Models, Tree Volume Prediction, Azardirachta indica and Warwade.