INTRODUCTION 



Today, as in the past, the accurate estimation of tree volume is an essential pre- 

 requisite for foresters involved with timber management planning, forest surveys, damage 

 appraisal, timber sale preparation, trespass, and condemnation proceedings as well as 

 growth and yield studies. To be of immediate value, volume estimates must be expressed 

 in units of measure related directly to the products derived from the tree. The board 

 foot and the cubic foot are traditional units of measure, although the latter is 

 increasing in importance as utilization of the total tree becomes more common. However, 

 it is also recognized that cubic foot volume, when combined with square feet of circum- 

 ferential surface and linear feet, provides for more consistent and accurate estimates 

 of a tree's product potential (Grosenbaugh 1954; Davis and others 1962; Bruce 1970). 

 Thus, future needs of foresters may well require estimates in these units of measure as 

 well as the traditional board foot. This paper is concerned solely with tree volume 

 estimation in the Southwest. Surface area equations for selected species in the same 

 area were provided by Hann and McKinney (1975) . 



All of the early volume tables and equations published for exclusive use in 

 Arizona, New Mexico, or both were for the prediction of unforked, gross Scribner board 

 foot volume to an 8-inch top. When volume equations were developed, the logarithmic 

 method described by Schumacl.cr zr/^ Hall (1933) was followed (Hornibrook 1936; Lexen and 

 Thomson 1938a, 1938b; Peterson 1939b, 1939c, 1939d; Lexen and Peterson 1939b, 1939c, 

 1939d; and Krauch and Peterson 1943). \Vhen this method did not work, the alinement chart 

 method was used (Peterson 1939a; Lexen and Peterson 1939a; and Krauch and Peterson 

 1943). These early equations and tables were for "blackjack" or immature ponderosa pine 

 (Hornibrook 1936; Peterson 1939b), "yellow" or mature ponderosa pine (Hornibrook 1936; 

 Peterson 1939c) , combined ponderosa pine (Peterson 1939d) , white fir (Lexen and Thomson 

 1958a; Lexen and Peterson 1939a), southwestern white pines (Lexen and Thomson 1938b; 

 Peterson 1939a), Apache pine (Lexen and Peterson 1939b), Arizona pine (Lexen and Peter- 

 son 1939c) , Chihuahua pine (Lexen and Peterson 1939d) , and Douglas-fir (Krauch and 

 Peterson 1934). 



In addition to these, Meyer (1938) published gross volume tables for unforked 

 ponderosa pine derived from data collected in several western States, including the 

 Southwest. Volumes were given in three units of measure--total stem cubic foot. Inter- 

 national 1/8-inch, and Scribner board foot. 



More recently, the logarithmic method has been used to develop equations for 

 unforked, gross Scribner board foot volume to an 8-inch top in white fir (Peterson 1958) 

 and in Englemann spruce (Peterson 1961) , and for unforked, gross cubic foot volume to 

 both a 4- and an 8 -inch top in immature and mature ponderosa pine (Gaines and Peterson 

 1960). Minor (1961) used weighted, least squares regression to develop an equation for 

 unforked, gross cubic foot volume to a 4-inch top in ponderosa pine, whereas Myers 

 (1965) used ordinary, least squares regression with segmented data to develop unforked, 

 gross volume equations for (a) total stem cubic foot volume, (b) merchantable cubic foot 

 volume to a 4-inch and variable top limit, and (c) International 1/4-inch and Scribner 

 board foot volumes to a variable top limit. (Myers used the term "variable top limit" 



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