A Model to Estimate Tree Size when Trunk Girth Cannot be Used

Abstract

Tree size measurements are usually taken to estimate the bearing potential of a tree, and also as a covariate to be used in the analysis of covariance in field experiments. The more simple measurement is trunk circumference, but in some cases this measure is not related to tree size, particularly in multi-trunk trees, in old trees with trunks showing geometry different to a cylinder, or in uncrowned trees. In such cases, the height and spread of the canopy is measured to calculate canopy volume, but this estimation is sometimes tedious and imprecise. In the present work, the relationship between trunk girth and the girth of the main branches (scaffold limbs) was determined in almond, walnut and olive trees to establish a model to estimate tree size. The experimental trees were trained in a vase-shape with trunks of 90 to 100 cm in height. The most accurate relationship between trunk girth and the girths of the main branches was TC= 1.6, BCwhere TCis the trunk circumference and BCthe average branch circumference. This model was validated for the three species and was applied to estimate tree size in multi-trunk olive trees. In these trees, an imaginary single-trunk was calculated for each tree using the previous model combining the individual trunk girths by adding them and dividing the sum by the number of trunks per tree. The imaginary single-trunk circumference was highly and significantly correlated to canopy volume and linearly related to fruit yield, suggesting that it could be a more precise and easy measure that may be used as a substitute of canopy volume to estimate relative tree size.