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Effect of competition on the growth and crown form of lodgepole pine Bailey, Gordon Raymond

Abstract

Tree growth and crown form of 131 open-grown and 63 forest-grown lodgepole pine were investigated. Areas sampled included representative sites in the Interior, Lower Mainland and Vancouver Island in British Columbia. Both graphical and multiple regression analyses were used. The best, but still inadequate, estimator of either radial or basal area growth for the last five years was the growth for the period six to ten years ago. Standard errors of estimate ranged from 21.4 percent for basal-area growth of individual open-grown trees to 43.5 percent for basal-area growth of individual forest-grown trees. More than 90 percent of the total variation in the crown width of open-grown lodgepole pine was accounted for by d.b.h. alone. For forest-grown trees only 56.8 percent was accounted for by d.b.h. This percentage may be increased to 81.1 percent by the addition of height-crown width (H/CW), and to 68.4 percent by the addition of crown width/diameter (CW/D). Average value for CW/D was 0.99 for the forest-grown, and 2.13 for 90 open-grown trees ten years of age or older. Both H/CW and CW/D are significantly related to site index and age. However, when d.b.h. is taken into account, only six percent of the variation in CW/D is affected by site index. Almost 50 percent of the height to the lowest dead branch, and over 90 percent of the height to the lowest live branch could be accounted for by tree age, d.b.h. and height. One of four "competition factors", all related to distance to, and size of, competing trees, accounted for an additional 13.7 percent of the variation in height to dead branches. However, basal area, H/CW, and CW/D were of little importance after the effects of age, d.b.h. and height were accounted for. The maximum growth rate for open-grown trees was determined graphically for ages from 30 to 50 years by site index classes. Comparison with normally grown trees showed that at least twice the normal yield-table-estimate of growth rate may be expected from open-grown trees. Using regression equations developed from the data, a theoretical conversion to lumber was made for a butt log from an open-grown tree. For boards, graded under the Western Pine Association's rules, it was shown that large knots may degrade lumber grown at the maximum rate. Therefore, use of an open-to-normal density model, which allows crowns to compete before excessive knot formation occurs, would be a desirable objective for management of lodgepole pine.

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