Evaluation of field performance of poplar clones using selected competition indices

Use of competition indices in the analysis of forestry experiments may improve detection and understanding of treatment effects, and thereby improve the application of results. In this paper, we compared the performance of 8 indices in an analysis of a spacing trial of four Populus clones planted in pure and mixed clonal plots. Indices were included as covariates in analyses of variance and evaluated on their ability to decrease mean square error. Indices that were simple to calculate (i.e., required only diameter and spacing or distance information) decreased mean square error by as much as 32%. We then illustrate the use of a simple index to assess clonal response to intraand inter-genotypic competition and to interpret treatment effects confounded by different levels of competition. In pure clonal plots (intra-genotypic competition), all the clones tested reacted similarly to competition, while the same clones tested in mixed plots (inter-genotypic competition) reacted differently to varying levels of competition. The use of a competition index to assess clone rankings within a mixed clonal plot can be an effective way to predict clonal performance within a mono-clonal planting.