Pacific Northwest Research Station

Title: Branch and crown dimensions of Douglas-fir trees harvested from old-growth forests in Washington, Oregon, and California during the 1960s

Author: Hummel, Susan S.

Date: 2009

Source: Northwest Science

Description: 

In temperate rain forests of western North America, some second-growth forests are managed to promote development of the multidimensional structures observed in old-growth forests. Information about tree architecture from across a range of growing conditions is needed to support this goal. Accordingly, branch and crown dimensions associated with tree age, site index, and stand basal area are reported for 854 Douglas-fir trees, which were harvested from old-growth forests in Washington, Oregon, and northern California in the 1960s. Sample trees ranged from 38 to 647 years old. The average diameter and the relative height of the first live and dead branch increased with tree age. In contrast, only weak relations existed between live crown ratio, which was highly variable, and tree age or site index. Differences between old Douglas-fir trees and younger trees with an equivalent breast-height diameter (dbh) were greatest in the dimensions of their first branches. Between ages 100 to 500 yr, for example, the mean first live branch on a 127-cm dbh tree was estimated to more than double in diameter--from 3.1 to 6.6 cm--at a basal area of 114 m2/ha. Despite the limitations associated with inherited data, study results have silvicultural implications for managed Douglas-fir forests because they indicate that crown morphologies of large, young trees were not the same as their similarly sized, older counterparts on sites spanning a range of average natural stand density conditions within the Douglas-fir region.

Keywords: Douglas-fir, western North America, old-growth forests, branch and crown dimensions

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Citation

Hummel, Susan S.  2009.  Branch and crown dimensions of Douglas-fir trees harvested from old-growth forests in Washington, Oregon, and California during the 1960s.   Northwest Science.