Figure 1 - Ponderosa Pine Diameter Increment versus Spacing

Figure 1 plots the results of plantings by Barrett, Schubert, Bolt planting 1, Boldt planting 2, and Boldt planting 3 (sequentially thinned). The graph shows that D+9 to 11 spacing at least doubles diameter growth rates found in natural unthinned stands.

Barrett's and Schubert's data are comparable. Both are about the same site index (80). Boldt's data follows a similar curvilinear relationship below Barrett's and Schubert's data. The site index is only 55 however. On Boldt's sequentially thinned plots the site index is 70.

Extra wide spacing by Barrett did not increase diameter growth rate.

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Last Modified: 07/05/2007