Characteristics of high- and low-vigor lodgepole pine trees in old-growth stands

Lodgepole pine (Pinus contorta var. latifolia Engelm.) trees in an old stand differed widely in appearance. Some appeared healthy, with deep crowns, high leaf areas, nearly conical-shaped crown tops, and branches with live needles extending well back from the tip. Others with similar-sized boles appeared to be in a state of decline, having much shallower crowns, lower leaf areas, crowns that were flattened at the top, and "tufted" branches with needles only near the ends of the branches. Ten trees, five each in these two apparent vigor classes, were selected from a one-hectare area of a mature stand. Trees in the two groups were found to have similar height, diameter at breast height, age, and total volume. As expected from the selection criteria, high-vigor trees had much deeper crowns (P = 0.01) and higher leaf areas (P = 0.10). The volume of heartwood in the bole was higher in the low-vigor trees (P = 0.08), and the volume of the sapwood was higher in the high-vigor trees (P = 0.13). Sapwood and heartwood ages were similar in both classes. This suggests that, in earlier years, low-vigor trees reached a larger volume, represented by the present heartwood, than did the high-vigor trees (i.e., the current vigor rankings are the reverse of what they had been). The ratio of sapwood volume to total leaf area was not significantly higher in the low-vigor trees (P = 0.24), although this ratio varied tenfold among the data. Results suggest that a physiological basis for assessing vigor involving leaf area, sapwood, heartwood, age, and incremental growth data would identify a continuum of response from high- to low-vigor trees rather than discrete groups based on visual appearance.