. Twenty-year growth of thinned and unthinned ponderosa pine in the Methow Valley of northern Washington. Introduction The Study Area Tree spacing of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) can have an impressive effect upon the eventual size of the trees, wood quality, the time to grow the desired product, and—frequently— the quantity and quality of the understory vegetation. Selection of spacing is one of the most significant decisions the forest manager makes, because it sets the stage for the dimensions of future harvests and interim value of other resources. Past research has sho
. Twenty-year growth of thinned and unthinned ponderosa pine in the Methow Valley of northern Washington. Introduction The Study Area Tree spacing of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) can have an impressive effect upon the eventual size of the trees, wood quality, the time to grow the desired product, and—frequently— the quantity and quality of the understory vegetation. Selection of spacing is one of the most significant decisions the forest manager makes, because it sets the stage for the dimensions of future harvests and interim value of other resources. Past research has shown that widely spaced ponderosa pine trees in the Pacific Northwest maintain rapid individual tree growth longer than closely spaced trees (Barrett 1973). Wide spacing, however, is usually accom- panied by losses in stand production until the area between trees is fully used. Barrett (1971) found some evidence to suggest that stands originating on similar sites and allowed to develop full crowns will yield almost the same amount of volume over a wide range of densities. If this is true,' then the question is whether the manager wants the wood in large or small trees. In most stands of ponderosa pine in the Pacific Northwest—as with many other species throughout the West —stand regulation is not that simple; stands that develop from natural seedings rarely have crowns that are free to expand. If they are widely spaced, the site is sometimes invaded by competing, brushy vegetation. In many natural stands, poor crown ratios and poor vigor are common because of high density and overstory suppression. As a result, the time to reach maximum production of useful wood is lengthened. This reduction in growth may be so subtle that the manager is unaware of the loss. Even if the loss is suspected, dealing effectively with it may be impossible because other resource values may be in jeopardy. Research objectives in this study were: • To provide estimates of stand growth for speci
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