Fifteen-year results from a Grand fir-Shasta red fir spacing study.

A 43-year-old, even-aged stand of advance reproduction of grand fir and Shasta red fir in central Oregon responded to release and thinning with diameter and height growth two to three times the prerelease rate. The response began the first growing season after the overstory was killed with 2,4-D. Diameter growth during the second and third 5-year periods after release increased significantly over that of the first 5 years. Differences in spacing had no effect on diameter growth during the first 5 years, but growth at the wider spacings increased considerably during the second and third periods. Increased growth after release suggested that saving true fir advance reproduction can be a desirable option, but the potential for losses from heartrot should also be considered.