Distance-Dependent Competition Measures for Predicting Growth of Individual Trees

Abstract

Abstract Modified distance-dependent competition indices were developed for predicting tree growth in plantations. These modified indices adjust the growth of an average tree up and down depending on the size of competitors as compared to the subject tree. A neighbor larger than the subject tree--dominant neighbor--places the subject tree at a competitive disadvantage, whereas a smaller neighbor--suppressed competitor--places it at a competitive advantage. Dead neighbors are included as a special kind of suppressed neighbor. Based on this philosophy, new versions and modifications of distance-weighted size ratio and area overlap indices were developed and compared to some previously published indices. Data from a spacing study established in eucalypt plantations in Portugal were used for the empirical aspects of this study. Single correlations with growth, on a spacing X age basis, were generally higher for the modified indices than for their original unmodified counterparts. Modified indices, in conjunction with stand-level variables, also performed well in multiple linear regression equations for predicting growth of individual trees. For. Sci. 35(3):816-831.