Growth Dominance In A Long-Term Red Pine Thinning Experiment

Forest stand development is driven by individual tree growth, which is a function of resource acquisition and resource-use efficiency. Although larger trees may have a greater opportunity to acquire resources, physiological constraints of larger trees may restrict their ability to convert resources into growth. One approach to understanding the consequences of resource acquisition and utilization on stand growth is to examine growth dominance, defined as positive when larger trees in the stand display proportionally greater growth than smaller trees, and negative when smaller trees have proportionally greater growth than larger trees. Binkley (2004; 2006) developed a method for quantifying stand-level growth dominance and proposed a hypothesis for how dominance progresses through stand development. We applied this approach to long-term red pine silvicultural experiments to characterize how stand age, thinning treatments (thinned from above, below, or both) and stocking levels (residual basal area) influence stand-level growth dominance through time. In stands thinned from below or from both above and below, dominance was not significantly different from zero at any age or stocking level. Growth dominance in stands thinned from above, by contrast, trended from negative at low stocking levels to positive at high stocking levels and was positive in young stands but not significantly different from zero in older stands. Growth dominance in un-thinned stands was consistently positive and increased with age, supporting Binkley’s hypothesis. These results suggest that growth dominance provides a useful tool for assessing the efficacy of thinning treatments designed to reduce competition between trees and promote even growth across a population