The data indicated no apparent advantage in using nonlocal red alder to reduce aboveground competition with Douglas-fir at this location. Survival of both sources of interplanted alder was high, and the average diameter and height were similar through plantation age 10. Retaining about 1100 volunteer alder per hectare (445/acre) through plantation age 7 had no measurable positive or negative effect on the associated Douglas-fir.

When alder densities are less than about 1 250/ha (500/acre), silviculturists can safely delay alder control on most average or below-average site quality land until 6 to 8 years after planting Douglas-fir. This reduces alder sprouting and permits combining complete or partial control of alder with precommercial thinning of associated Douglas-fir. To ensure timely control, periodic observations of Douglas-fir red alder mixtures are necessary, however.

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