Conditioning a distance-dependent competition index to indicate the onset of inter-tree competition

Abstract

Data from a loblolly pine ( Pinus taeda L.) spacing trial were used to investigate relationships between a distance-dependent competition index (CI) and the inflection age of sigmoidal single-tree cumulative basal area curves. Inflection ages increased with increasing initial growing space (GS), consistent with the hypothesis of maximum usable GS. Competition intensity as measured by the CI was generally smallest at a given point in time for trees with large inflection ages, but the trend varied by planting density. CI values at the inflection age also varied with planting density. The CI was modified so that it gave a constant CI value at the inflection age, on average, across all planting densities. Effects of site quality were accounted for to a limited degree, but the range of sites was narrow in the spacing trial. The modified CI should be useful as an absolute measure of competition independent of spacing.