Evaluation of competition indices in modelling the increase in diameter of tree species in Mixed Ombrophilous Forest

Abstract

This study aimed to evaluate distance-dependent and distance-independent competition indices and their effect in modelling the periodic annual increment in diameter (PAId) of five tree species in a Mixed Ombrophilous Forest. Data were recorded from permanent plots installed and monitored every 3 years in the period 2002–2017 in the National Forest of Irati, Paraná, Brazil. Ten distance-dependent and distance-independent competition indices were evaluated based on Spearman’s correlation coefficient between each index and the periodic annual increment in diameter over the study period (15 years), evaluating the selection range of competing neighbours in the distance-dependent competition indices. Individual tree models were also developed to estimate the PAId of each species and for all forest species with four different approaches (depending on the competition indices tested) by the ‘stepwise’ procedure. All distance-independent indices generally showed moderate correlation with the growth of individual trees, with an emphasis on the Stage, Corona and Ferrara, Glover and Hool, and Lorimer indices. The distance- dependent competition indices showed stronger correlations with PAId using radii of 10, 15, 17 and 20 m. The PAId models, derived from 3-year monitoring periods and incorporating intermediate diameter as an input variable, consistently produced superior estimates compared to the other models, although their practical application is difficult. This study provides insights into the inclusion of competition indices in diameter increment models in the context of individual tree-level modelling in Mixed Ombrophilous Forest.