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Stem form responses to differing areas of weed control around planted Douglas-fir trees Robin Rose, Douglas A. Maguire, and Scott Ketchum Department of Forest Science Oregon State University
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Introduction Discerning differences in stem form and volume among silvicultural treatments.
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Introduction DBH and height respond to control of competing vegetation. Consequently stem volume also responds to vegetation control.
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Introduction As trees develop under intensive management: Form differs from a cone ( /12)D 2 H, Trees large enough for existing volume or taper equations.
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Introduction Application of volume and taper equations: Regional development; May not include intensively managed stands; Averages lose subtle differences;
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Introduction Volume and taper equations: Most are functions of only DBH and HT. Consequences: Insufficient for detecting treatment differences.
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One solution Measure upper stem diameters. Assess existing volume or taper equations. Develop new site-specific equations.
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Past work Upper stem measurements were made at sites near Marcola and Summit: Fit Kozak’s variable-exponent taper equation: Tested parameters across treatments; No treatment effect was found.
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Past work Compared empirical volumes to Bruce and DeMars (1974) volume estimates. Bias increased with progressively more weed control.
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Past work Compared volumes to a cone Control: Cone underpredict volume, Trees more parabolic. Weed control: Cone overpredicts volume, Tree more neiloid.
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Objective Compare upper stem measurements to those predicted by Jim Flewelling’s taper system.
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Methods Sites Summit, OR: Central region of the Oregon Coast Range. Marcola, OR: Western Cascade Mountain foothills.
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Summit Marcola
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Methods Experimental design Completely randomized design, 8 treatments, 3 replicates, Plot area = 0.112 ac, 49 seedlings planted at 9.8 ft square spacing.
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Methods Treatments No herbicide, 4 ft 2 full control, 16 ft 2 full control, 36 ft 2 full control, 64 ft 2 full control, 100 ft 2 full control, 100 ft 2 woody vegetation control, 100 ft 2 herbaceous vegetation control.
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1-ft 2-ft 3-ft 4-ft 5-ft 4 ft 2 64 ft 2 16 ft 2 36 ft 2 100 ft 2
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Methods Diameter outside bark was collected at tree base, breast height, 8 ft, and every 4 ft above 8 ft. Observed DOB’s were compared to those predicted by Flewelling system. Consistent bias – inferences unaffected Changing bias – inferences questionable
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Results Average differences: Summit: DOB overpredicted Across most of stem profile Marcola: Low at upper and lower stem positions. High at middle stem positions.
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Results Averages by treatment: General overprediction over stem profile Largest overpredictions: Upper stem positions Greater for more intensive control
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100 0 4
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Discussion If Flewelling predictions are regional averages: More intensive weed control Narrower upper stem profiles. Less intensive weed control Slightly narrower lower stem profiles.
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Results Treatment differences by site: Marcola: Underpredicts near base (greater weed control); Underpredicts near top; Overpredict near middle of tree.
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100 0 4
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Results Treatment differences by site: Summit: Overpredicts over entire stem profile; Overpredictions increase with greater weed control.
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100 4 0
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Conclusions Biases in predicted DOB’s are small. Systematic bias among treatments. Bias the estimated effects of treatments on stem profiles. Formal statistical analyses on implications are continuing.
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