Graduate Thesis Or Dissertation
 

Growth of plantation conifers and whiteleaf manzanita in southwest Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/t148fk20n

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  • Southwest Oregon presents an environment of hot dry summers, cool moist winters, and rocky, shallow soils. The establishment of conifer plantations in this region presents challenging problems for initial seedling survival and subsequent growth. Three areas of concern include early conifer growth after seedling establishment, growth of competing hardwoods within the conifer plantation ecosystem, and the difficulty of estimating site index with early conifer growth. Analysis of early conifer growth, in four different plantations, illustrates the influence of various levels of indigenous hardwoods during the first fifteen years after planting. Growth patterns resulting from differences in woody competition during the first five years after planting continue to diverge. Trees that have grown without woody associates show no signs of slowing prior to attaining a commercial size. Conifers growing under the most severe level of whiteleaf manzanita competition have either died, are suppressed, or appear chlorotic. Each of four plantations show similar growth response patterns to the influence of hardwood competition. Early competition is strongly associated with growth to age fifteen. Whiteleaf manzanita regenerates naturally on many low elevation sites after mechanical site preparation. I examine the growth of whiteleaf manzanita, at varying densities, within the confines of a conifer plantation ecosystem. Growth prediction equations are for height, basal diameter, biomass per individual, and biomass per hectare. The accumulated biomass after 13 years of growth is substantial and may present an economic opportunity for the production of fiber. Competing hardwoods complicate the estimation of site index in young conifer plantations. Conifer growth appears to be highly plastic, thereby confounding attempts to estimate site index accurately. I present correction factors for estimating site index in young conifer plantations growing on poor sites in southwest Oregon. These correction factors utilize the density of hardwood cover as an independent variable. The density of hardwoods, hence the intensity of silvicultural activities to control competing hardwoods, is a major determinant of stand productivity and estimation of site index. The areas of conifer growth, hardwood growth, and site index, are all integral parts of long-term land management planning.
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