Brush reduces growth of thinned ponderosa pine in northern California

Abstract

The effects of tree spacing and brush competition were evaluated on a ponderosa pine (Pinus ponderosa Dougl. ex Laws. var. ponderosa) site of low productivity in California's North Coast Range. Eleven-year-old saplings were thinned to square spacings of 2.1, 2.4, 3.0, and 4.3 m (7, 8, 10, and 14 ft), and all, half, and none of the understory brush (principally manzanita [Arctostaphylos sp. J) manually removed in a split-plot design. Analysis of variance showed that brush crown cover was significantly related to periodic annual increment in diameter-at-breast-height, height, and volume of the pines. Spacing significantly influenced diameter growth only when all brush was removed. A nonlinear equation relating brush cover and trees per hectare to periodic annual increment in diameter explained 90 percent of the variation. The results suggest that, for the plantation studied, any amount of brush will restrict diameter growth. When cover exceeds 20 to 30 percent, brush competition overwhelms intertree competition, and trees grow at about the same rate regardless of spacing.

Citation

Oliver, William W. 1984. Brush reduces growth of thinned ponderosa pine in northern California. Res. Pap. PSW-RP-172. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station. 7 p.