A new approach to assessing competition from trees on Nelder wheels

Aim of the study: To develop an index to describe the competition of trees of Eucalyptus spp. clones in different densities; also, to evaluate the productivity of the clones on Nelder wheels (NWs). Area of study: Ten Eucalyptus spp. clones distributed in nine NWs, located in the northern state of Tocantins, Brazil. Material and methods: A new competition index was formulated as the ratio of geometric areas and average cross-sectional areas of sampling units from different locations on the NW referenced to a unit taken in the center of it. Besides, two distance-dependent indices were tested to evaluate their performance in different spacings. The correlation between the competition indices and the variables height, diameter, volume and cross-sectional area, average distance and mortality percentage was evaluated. To check the difference in productivity between the clones we used MANOVA and discriminant analysis. Main results: The Alba-Péllico index provides a better understanding of the competitive relationship between trees, as well as a better explanation of the competitive process in the NWs than the other indices evaluated. The variation in the basal area between the clones in the less dense locations, substantiates the characteristics of each clone or possible interferences of the location since in this condition they are free from the influence of spacing and competition. This shows that competition is more influential than other characteristics of sites and genotypes in the behavior in diameter, basal area and volume in the densest sites. Research highlights: The characteristics of the Alba-Péllico index indicate good interpretation to understand the competitive relationship among trees since the results vary between 0 and 1, and the closer to zero the smaller or non-existence of competition.