Comparative Effects of Precommercial Thinning, Urea Fertilizer, and Red Alder in211 a Site 11, Coast Douglas-Fir Plantation

摘要

The authors varied the number of red alder retained with 300 Douglas-fir per acre211u001eon a high-quality site in coastal Oregon. Alder densities of 0, 20, 40, and 80 211u001eper acre were tested. The authors' fifth treatment eliminated nitrogen-fixing 211u001ealder, but substantial nitrogen fertilizer. Treatment 6 had neither thinning nor 211u001ealder control. Treatments were randomly assigned within each of three blocks in a 211u001e9-year-old plantation. Stand density was reduced within 15 of these 18 211u001eexperimental units. Surplus conifers were cut, but surplus red alder were 211u001econtrolled by the 'hack-and-squirt' method. Because numerous trees of other 211u001especies regenerated naturally, combined density of all species before thinning 211u001eranged from 1,400 to 5,700 trees per acre. Subsequent 17-year change in number, 211u001eaverage height, basal area, and volume of Douglas-fir were compared. Retaining 211u001e20, 40, or 80 alder per acre reduced numbers of associated Douglas-fir by about 211u001e10, 17, and 23 percent, respectively. In pur Douglas-fir plots, gross volume 211u001egrowth was similar for nonfertilized and fertilized plots, indicating no 211u001emeasureable benefits of additional nitrogen. in mixed stands, red alder reduced 211u001eyield of associated Douglas-fir, but not yield of combined species. Similar 211u001ecomparisons are needed at other locations, especially those with known nitrogen 211u001edeficiency.