Can Selection Thinning Convert Even-Age Douglas-Fir Stands to Uneven-Age Structures?

Uneven-age management of Douglas-fir (Pseudotsuga menziesii) stands can be used to address aesthetic, wildlife habitat, biodiversity, and sustainability concerns, but there has been little long-term experience with this type of management. To develop timely information on converting even-age stands to uneven-age forests, we used retrospective stand reconstruction methods to document harvest frequency, intensity, and stand structural development at four sites in western Oregon. We studied stands managed by selection thinning and identified strategies for creating and managing uneven-age forests. Selection thinning benefited mid- and understory trees and stimulated natural regeneration. Although stand growth was less than expected from low thinning, growth per unit of growing stock was similar to that in unmanaged stands. Douglas-fir often dominated regeneration and had satisfactory vigor at stocking levels about half that considered full stocking for even-age management, but good growth of regeneration may require even lower overstory stocking. Shade-tolerant grand fir and western hemlock, however, were more abundant at higher stocking levels. Selection thinning of young Douglas-fir stands can sometimes be effective in promoting viable regeneration while providing regular income and biodiversity. Because this was a retrospective study only, further, long-term testing is necessary.