Development of vegetation in a young ponderosa pine plantation: effect of treatment duration and time since disturbance

Abstract

The density and development of deerbrush (Ceanothus integerrimus Hook. & Arn.), other shrubs, forbs, graminoids, and ponderosa pine (Pinus ponderosa Dougl. ex Laws. var. ponderosa) seedlings were evaluated in a young plantation in northern California from 1988 through 1997. Treatment regimes consisted of manual release (grubbing) over 3 to 6 years and resulted in vegetation recovery times of 4 to 10 years. Revegetation was remarkably diverse, rapid, and vigorous. At the end of the study, the dominant shrub, deerbrush, had significantly lower average density and foliar cover relative to the control when treated either the first 3 years or the second 3 years, but average height was similar regardless of treatment. Average density of the 11 other shrubs was statistically higher in the control relative to other treatments, but cover and height did not differ. Density, foliar cover, and height of the forbs and graminoids did not differ among treatments at the end of the study. In the control, deerbrush plants numbered 6,100 per acre; other shrubs, 2,550 per acre; forbs, 27,300 per acre; and graminoids, 5,800 plants per acre in 1997. Foliar cover of deerbrush at 22,700 ft2 per acre was more than five times that of all other naturally established species combined and slightly exceeded that of pine seedlings in all treatments. Average height of pine seedlings ranged from 7.7 ft with intensive release to 5.6 ft with no release. In general, release statistically improved pine growth regardless of timing or duration, but delayed release was more costly.