Field and Computer Application of Mesavage and Girard Form Class Volume Tables

Mesavage and Girard form class volume tables for estimating board foot volume of standing trees remain the most widely used volume tables in the East and South even though newer, more versatile and sophisticated volume functions are available. The volume tables are being misused by foresters because the merchantability standards of the average, upper-log taper table used to derive the volume tables does not show that merchantable top diameters and form class applications require appropriate sampling and accurate measurement of form on selected trees. The original upper-log tapers, developed from averages of actual tree measurements and ocular estimates, were fitted to a regression model to smooth the inconsistencies of the table values. The resulting Mesavage and Girard "taper equation" is used to obtain upper stem diameters for trees of known Girard form class, dbh, and merchantable height. The taper equation shows that top-limit diameter increases with both tree size (dbh and height) and Girard form class, and any attempt to apply form class volume tables to a fixed-top diameter on inventory trees would produce erroneous cruise volumes. The derived taper equation can be used in an iterative procedure during computer applications to obtain single tree volumes as the sum of log segment volumes for segments of user-defined length. A hierarchy of suggested form class application options is presented along with suggestion sampling, measurement, and stratification procedures. South. J. Appl. For. 22(2):81-87.