Tree-Level Patterns of Lodgepole Pine Growth and Leaf Area in Yellowstone National Park: Explaining Anomalous Patterns of Growth Dominance Within Stands

Binkley, Dan; Kashian, Daniel

Abstract The growth of forests is the simple sum of the growth rates of all the trees. The growth of individual trees results from non-linear competition among trees for resources, including efficiency in the use of resources to grow stems, and these characteristics may change as trees and forest age. Lodgepole pine (Pinus contorta) forests in Yellowstone National Park showed an unusual pattern of low dominance of large trees (=reverse growth dominance), and we hypothesized this pattern resulted from a pattern of declining resource use efficiency (defined as wood growth per unit of tree leaf area) for large, old trees. Across a 96-site chronosequence, the largest trees continued to increase growth with age. Leaf area increased faster with tree size than did growth, leading to lower growth efficiency for large trees in stands older than about 125 years. These patterns contrasted strongly with those from a similar study with fast-growing Eucalyptus saligna, where strongly positive growth dominance resulted from greater growth efficiency across all sizes and ages. The hypothesis was supported, as the reverse growth dominance was associated with declining resource use efficiency in large, old lodgepole pine trees. Several factors may contribute to the declining growth efficiency of large, old pines, and the contribution of these potential factors could be determined from further investigation.