Graduate Thesis Or Dissertation
 

The influence of stand structure and topography on growth, leaf area and efficiency of young Douglas-fir in the Oregon Coast Range

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  • The relative influences of stand structure and topographic variation on volume growth, photosynthetic surface area, and stem growth efficiency were determined for six 17 to 23 year old well stocked stands in the central Oregon Coast Range. Plots were assigned to topographic classes (aspect, slope steepness, and slope position), by which stand density, stand growth and efficiency, and individual tree size and growth were compared. Plots were also assigned to classes according to the hardwood content and the same characteristics compared. In addition, individual trees were assigned to and compared by crown dominance classes. Multiple regression analyses were performed to show correlations of growth and efficiency variables with stand structure and topography variables. Results showed that not only stocking levels but also stand structure influence both stand and individual tree volume growth and efficiency. At a given Relative Density, stands with a lower stem density of large trees grew more volume and were more efficient than stands with many small trees. In addition, stands with more variation in tree size were more efficient than were more uniformly sized stands. The effect of stand structure overrode the effect of topography on growth and efficiency with two exceptions: stand volume growth and efficiency were higher on southerly than on northerly aspects and in areas of higher rainfall. In these areas, stands of a given density carried more leaf area, which may help to explain why growth was better there. In the regression analyses, stand volume growth correlated positively with Douglas-fir stand basal area, average annual rainfall, Relative Density, and an aspect variable that indicated better growth on southerly aspects. Stand volume growth correlated negatively with stem density of Douglas-fir. Stand leaf area correlated positively with stand basal area, average annual rainfall, stem density, and south aspects. Stand stem growth efficiency (volume growth per unit of leaf area) correlated positively with Relative Density, individual tree size variance, and southerly aspects, and correlated negatively with stem density and leaf area. Individual tree growth was mostly determined by the tree basal area, although there was a small negative effect of increasing stand basal area. The more dominant a tree was in a stand the greater was its growth, but suppressed trees were the most efficient, whether efficiency was calculated in terms of stem volume growth per unit individual tree leaf area or basal area growth per unit individual tree basal area. The presence of hardwoods of the small size and low densities in this study had no effect on absolute growth, however Douglas-fir grew more efficiently in pure stands than when mixed with hardwoods.
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  • Master files scanned at 600 ppi (256 Grayscale) using Capture Perfect 3.0.82 on a Canon DR-9080C in TIF format. PDF derivative scanned at 300 ppi (256 Grayscale + 265 b+w), using Capture Perfect 3.0.82, on a Canon DR-9080C. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
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