Equations for predicting sapwood area at crown base in southwestern Oregon Douglas-fir

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Abstract
Two basic taper models were analyzed for their ability to predict sapwood area at crown base. Sapwood areas were estimated on stem cross sections by measuring sapwood radii on the longest and perpendicular to longest axes and by assuming conformity to an ellipse. These data were collected on 2 to 14 points along the stems of 72 Douglas-fir trees in southwestern Oregon. Across the range in diameter at breast height, total height, and height of crown base, quadratic-quadratic segmented polynomials (T. A. Max and H.E. Burkhart. 1976. For. Sci. 25: 283-289) provided more consistent monotonic taper from breast height to crown base than F. A. Bennett and B. F. Swindel models (1972. USDA For. Serv. Res. Note SE-179). A model for predicting breast height sapwood area from only diameter at breast height, total height, and height to crown base is also presented.