Pacific Southwest Research Station

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Title: Vegetation Trends in a 31-Year-Old Ponderosa Pine Plantation: Effect of Different Shrub Densities

Author: McDonald, Philip M.; Abbott, Celeste S.

Date: 1997

Source: Res. Paper PSW-RP-231. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 35 p

Station ID: RP-PSW-231

Description: On a poor site in northern California, a brushfield community was treated in various ways which left initial densities of no shrubs, light, medium, and heavy shrubs. Density and development (height, foliar cover, crown volume) for three shrub species (alone and combined), one grass, and planted ponderosa pine in these categories were quantified from 1966 to 1992. Successional trends (ascendance and decline) are presented for these species and for forbs from 1962 (the date pines were planted) through 1992. Regression equations that model density and development are presented for the shrubs and pine. In general, greenleaf manzanita prospered during the study; snowbrush initially developed well, but then declined; Sierra plum endured, but was relegated to the understory; needlegrass invaded rapidly, peaked early, and was mostly gone by the end of the study. Only a trace of forb species remained by study end. Needlegrass displayed strong environmental preference, becoming dense and developing well in shrub-free areas, but was scarcely present in heavy shrubs. Ponderosa pine grew well in no-shrub plots, fairly well in light-shrub plots, and poorly in medium- and heavy-shrub plots. Extensive testing showed that shrub foliar cover and crown volume per acre explained more variation in several pine parameters than shrub height or density.

Key Words: density, development, grasses, plant succession, ponderosa pine, shrubs

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Citation

McDonald, Philip M.; Abbott, Celeste S.  1997.  Vegetation Trends in a 31-Year-Old Ponderosa Pine Plantation: Effect of Different Shrub Densities   Res. Paper PSW-RP-231. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; 35 p.