The 10-year growth response from an initial spacing study established in a ponderosa pine (Pinus ponderosa Dougl, ex Laws.) and grand fir (Abies grandis (Dougl. ex D. Don) Lindl.) plantation was measured in central Oregon. The study was designed to compare the growth rates of pure pine, pure fir, and a 50-percent mixture of each species planted at 6-, 12-, and 18-foot spacings. Height growth of pure pine was about twice as great as that of pure fir because of damage to the fir from frost and animals; growth of the pine-fir mixture was intermediate. Both basal area and total cubic volume increment per acre increased at the narrower spacing but diameter growth per tree was less. The height advantage of the pine is likely to be maintained in the future.
Seidel, K.W. 1985. A ponderosa pine-grand fir spacing study in central Oregon: results after 10 years. USDA Forest Service PNW Research Note No. 429. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 8 p