Growth of Lodgepole Pine Thinned to Various Densities on Two sites with DifferingProductivities in Central Oregon

摘要

Plots in two natural lodgepole pine (Pinus contorta Dougl. ex Loud.) stands withdiffering productivities were repeatedly thinned to one of five growing-stock levels (GSLs). Bole area was used to define GSLs. A linear relation between stand density index (SDI) and bole area was found after each thinning on the highly productive site, but the slope of this relation decreased with successive thinnings as trees grew larger. On the site with intermediate productivity, the upper limit for bole area was higher and a curvilinear SDI-bole area relation occurred. A constant bole area level probably does not represent the same competition level across a range of tree sizes. Low incidence of mortality caused by mountain pine beetle (Dendroctonus ponderosae Hopkins) occurred at SDIs below 170 for both sites. Concave curvilinear decreases in diameter growth occurred with increasing GLSs. Significant decreases in height growth with increasing GSLs were not detected. A convex curvilinear increase in gross basal-area growth and cubic-volume growth took place with increasing GLSs. Gross total cubic-volume PAIs increased with increasing SDIs for both sites until stand densities reached 95 percent of the normal stand SDI. This cubic-volume PAI-SDI curves then flattened with increasing SDIs. Maximum cumulative net cubic-volume (total and merchantable) and board-foot yields were produced at the intermediate growing-stock level at the high site. Little apparent differences in these yields occurred among the four highest GSLs at the intermediate site. Net total cubic-volume yield was higher for the three highest GSLs than net yields for unmanged stands from yield tables at comparable sites and ages.