Competition among loblolly pine trees: Does genetic variability of the trees in a stand matter?

The intensity of intraspecific competition among trees in a stand was compared for seed origin versus clonal origin stands of loblolly pine using tree size-based competition indices. A method that uses maximum likelihood with simulated annealing (MLSA) and one that uses discrete radii with simple correlation coefficients (DRSC) were applied and their results compared to stand level observable effects of competition. DRSC was found to give estimates of competitor search radii that were reasonable and in line with observable stand level effects of intraspecific competition. MLSA appeared to overestimate the optimum competitor search radius, had the potential to give estimates of the competitor search radius that were not unique, and was generally not conclusive on which genetic variety had the most intense level of competition among trees in its stand. The DRSC approach provides a simple alternative to MLSA where the assumptions behind MLSA do not hold or where it may not be easy for them to be checked. A comparison of competitor search radii in the different genetic variety stands and the observable stand level effects of competition did not find evidence to support the hypothesis that greater genetic uniformity among trees in loblolly pine stands would result in more intense intraspecific competition among the trees in the stand.

► Comparing competition intensity in forest stands.
► Discrete radii with simple correlations a better alternative.
► Maximum likelihood with simulated annealing not conclusive.
► Competition in clonal versus non-clonal stands of loblolly pine.
► Clonal stands do not necessarily experience more intense inter-tree competition.