Overview

In the late 1970s, the outlook for conifer seedlings in new plantations in the Western United States was dismal-too many were dying or growing below the potential of the site. This situation was untenable, and a large study aimed at increasing the survival and growth of planted conifer seedlings was implemented. This was the National Administrative Study on Vegetation Management of which the California portion is reported here. This study was really a program on plantation release with 32 individual studies that resulted in more than 60 publications over a 25-year timeframe. The authors emphasized plant community development and biological influences to help explain why some direct release methods were effective and some were not. Survival and growth of several species of conifer seedlings were correlated to the density, foliar cover, and height of various combinations of over 235 species of hardwoods, shrubs, forbs, and graminoids after application of five principal release techniques (herbicides, manual release, mulches, grazing, and mechanical [large machines]). Herbicide use was the most effective treatment followed by manual release and mulches. Domestic grazing, as currently practiced, was not effective, and release with large machines was worthwhile only if followed by an herbicide. Genetic enhancement of conifer seedlings showed promise as a vegetation management tool at first, but lost its efficacy later. Indirect vegetation management by using shade and organic material to reduce the growth and density of competing vegetation has potential, but needs more study. Nineteen principles and 10 conclusions resulted from this research program, but more work in the form of 11 challenges is recommended.

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9781480132924

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