Role OF Structural Indices and Other Spatial Measures in the Improvement Of Crown Variables Prediction For Lannea fructicosa

Abstract

Theoretically, the stem of the tree must be strong enough to withstand the forces that act on it. These forces include the weight of the crown and the drag exerted on it by the wind. This mean that for a well-established root system, there should be some kind of balance between crown and stem sizes, otherwise the stem be break. The sizes, shapes and relative locations of crowns both determine and respond to the shading and constriction effects that characterize aboveground interactions between trees. Due to this kind of balance, tree crown parameters have been used as predictor variables in diameter and height growth equations. Although the correlation between tree variables and crown dimensions has well documented in the literature, other stand composition and conditions such as competition, elevation and aspect are believed to be among the unexplained forces that exert strong influences on the accuracy of the allometric models used for that relationship. This study attempted to quantify the effect of structural indices and other spatial measures to improve the prediction of crown radius and crown length for trees in natural woodlands. Field data were recorded for Lannea fruticosa tree species that naturally grown in Elgarri forest reserve in Blue Nile State, Sudan. The data was used to test the performance of estimating crown dimensions on the basis of allometric relationships with tree diameter and height. A total of thirteen spatial and non-spatial indices were incorporated into modified crown dimension models. Coefficient of multiple determination (R2) and relative bias were used to test the performance of these indices in improving the accuracy of estimates. According to the results all predictions of crown length and radius were found to be better after the incorporation of the spatial and non-spatial, with positive R2 gain and acceptable negative bias values for crown radius and positive ones for crown length. For all cases, the spatial indices were found to be better than the non-spatial ones.