Estimating the surface area of spruce and pine foliage from displaced volume and length

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Abstract
Accurate determination of the surface area of needle-leaved trees is a basic requirement for many types of physiological or growth analysis studies in forest research. While many methods are available to estimate surface area, there is still a need for an accurate, rapid measurement technique for species with three- or four-sided needle morphology. I propose a regression technique with length and displaced volume as the independent variables. The regression technique is an improvement over the use of displaced volume and length in direct geometric calculation as it does not assume a constant needle morphology. The regression technique gives more accurate results than direct calculation, is comparable in precision, and is necessary to counter bias where variation in the cross-sectional shape of foliage is related to the treatment or variable under study. Use of regression, however, requires that a subsample of foliage, representing the range of conditions to be studied, be sectioned and measured directly for surface area to develop the estimation equation.