Initial and continued effects of a release spray in a coastal Oregon Douglas-fir plantation

Portions of a 4-year-old Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) France) plantation were sprayed with herbicide. Five years after spraying, we established 18 plots and used several means to determine retrospectively that six plots probably received full spray treatment and six others received no spray. Various portions of the remaining six plots probably were sprayed. Herbicide reduced number and size of red alder (Alnus rubra Pong.), increased number and size of planted Douglas-fir, damaged terminal shoots of Douglas-fir resulting in more abnormal boles and branching, and increased number of volunteer conifers. Fifteen of the eighteen plots were thinned. In the subsequent 6 years, thinned plots that had received full release at age 4 averaged 9 percent more volume growth (all species) than plots not released.