. Ponderosa pine saplings respond to control of spacing and understory vegetation. Ponderosa pine; Ponderosa pine Spacing. Other Thinning Effects The tree spacing to be selected in a precommercial thinning depends, in part, upon the total "product mix" desired from the forest, that is, wood, water, and forage. Narrow spacings tend to increase total wood production, if small trees can be used. On the other hand, wider spacings tend to favor forage and water production. Therefore, an understanding of the effect of thinning on forage and water is important in selecting an appropriate in
. Ponderosa pine saplings respond to control of spacing and understory vegetation. Ponderosa pine; Ponderosa pine Spacing. Other Thinning Effects The tree spacing to be selected in a precommercial thinning depends, in part, upon the total "product mix" desired from the forest, that is, wood, water, and forage. Narrow spacings tend to increase total wood production, if small trees can be used. On the other hand, wider spacings tend to favor forage and water production. Therefore, an understanding of the effect of thinning on forage and water is important in selecting an appropriate initial Figure pine saplings thinned to a wide spacing (1959). Understory vegetation left (top). Understory vegetation removed (bottom). Forage.—Thinning stimulated not only growth in diameter and height of trees but also growth of understory vegetation (figs. 10 and 11). Four years after thinning, it was obvious that most thinned plots in this experiment where understory was left had considerably more understory vegetation than nearby un- thinned stands. Furthermore, by this time there was a tendency for greater amounts of understory vegetation to occur at wider spac- ings except for the widest spacing. By 1967, we were tempted to speculate that vegetation was responding to the additional amounts of light, soil moisture, and nutrients provided by wider spacing, as differences in amounts of vegetation present at the various spacings were significant at the 5-percent level of probability. In addition, orthogonal compar- isons showed a trend toward more understory vegetation at wider spacings, although the 125-tree-per-acre treatment averaged more understory vegetation than the 62-tree-per- acre treatment (as indicated in figure 11). Statistical tests showed no real difference between the two treatments. Vegetation crown cover increased with time through all the spacings tested (fig. 11). For example, at the spacing, density percentages ranged fro
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