Graduate Thesis Or Dissertation

 

Construction of regression models for predicting crown development in southwestern Oregon Douglas-fir Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/707959725

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  • A branch mortality dating technique and whorl sampling strategy were implemented to model five-year crown recession from data collected on temporary plots. Twenty-eight Douglas-fir from two levels-of-growing- stock studies in Oregon and Washington were first dissected to validate the proposed dating technique and assess alternative sampling strategies. Branch mortalities in 10-15 whorls below crown base were dated by locating discontinuities between branch and bole growth rings in stem cross-sections. Along with height measurements to the sample whorls, this technique allowed reconstruction of past crown base positions. Backdated heights to crown base corresponded closely with 15-year repeat crown measurements taken on the same trees. Seven sampling strategies (sampling scheme and estimator) were assessed for their ability to estimate past five-year crown recession by sampling only two to four whorls per tree. Simple linear regressions of estimated on actual recession for various five-year intervals suggested that a two-whorl sampling scheme with an appropriate estimator would perform adequately on temporary growth plots. This sampling strategy was applied to 357 Douglas-fir from temporary growth plots in southwestern Oregon. Numerous nonlinear and logarithmic models were developed to predict five-year crown recession from other tree, stand, and site variables. Residual analyses and indices of fit demonstrated that a multiplicative model with lognormal errors was the most appropriate model form. Sapwood taper above breast height was modeled with a quadratic-quadratic segmented polynomial. This taper function allowed extrapolation or interpolation of sapwood area measurements near crown base to sapwood area at crown base. Transformation of gross crown dimensions into expressions of conic surface area yielded accurate predictions of sapwood area at crown base. These expressions were therefore inferred to reflect equally well the total leaf area of individual Douglas-fir trees in southwestern Oregon. Modeling at the resolution of gross crown dimensions therefore possesses both the physiological appeal of providing an accurate index of the tree's relative photosynthetic capacity and the conceptual appeal of portraying competition for light and aerial growing space.
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