. Twenty-year growth of thinned and unthinned ponderosa pine in the Methow Valley of northern Washington. 62 125 250 500 Unthinned TREES PER ACRE Figure 11.—Average annual net cubic-volume increment ot ponderosa pine during the first, second, third, and fourth 5-year growth periods, and increment on a comparable number of the best well-distributed trees in the unthinned stand. YEARS SINCE THINNING 0 5 10 15 20 (25) (30) 2600 -. 0 I i I ! I I 1 1— 47 52 57 62 67 (72) (77) AGE Volume Increment and Yield The effect of spacing on volume increment was significant (table 1). Periodic volume incremen
. Twenty-year growth of thinned and unthinned ponderosa pine in the Methow Valley of northern Washington. 62 125 250 500 Unthinned TREES PER ACRE Figure 11.—Average annual net cubic-volume increment ot ponderosa pine during the first, second, third, and fourth 5-year growth periods, and increment on a comparable number of the best well-distributed trees in the unthinned stand. YEARS SINCE THINNING 0 5 10 15 20 (25) (30) 2600 -. 0 I i I ! I I 1 1— 47 52 57 62 67 (72) (77) AGE Volume Increment and Yield The effect of spacing on volume increment was significant (table 1). Periodic volume increment also showed a trend toward increase with time in all thinned treatments (fig. 11). Trees on plots at various densities of 62, 125, 250, and 500 trees per acre produced 62, 92, 107, and 114 percent of the volume produced by the unthinned plots during the last period. This annual increment will probably increase until maximum capacity for growth for a given density is reached. The larger, dominant trees in the unthinned stand are not contributing much volume increment. For example, the 125 largest trees in the unthinned stand produced only 16 percent of the volume grown by all the trees in the unthinned stand (fig. 11), indicating that even the dominants are suffering severe competition from other trees in this natural, dense stand. Although the unthinned stand presently contains the highest amount of wood fiber (fig. 12), the volume is distributed on trees that have an average diameter of a little less than 4 inches. Compare this to trees at the widest spacing that now average 11 inches in diameter. The relation of volume increment to stand density for ponderosa pine, over a range of sites and plant communities in the Pacific Northwest, needs to be deter- mined. As a beginning, volume increment related to basal area and stand-density index (SDI) (Reineke 1933)6 in this study are presented in figures 13 and 14. 6 Personal communication with Donald DeMars. Pacific Northwest
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