SITE INDEX 

 AND 



YIELD CAPABILITY 

 EQUATIONS 



The information in this section was derived either from published material or from 

 data in the files of the Intermountain Forest and Range Experiment Station, as will be 

 noted for each particular species. The mathematical details of equation construction 

 or derivation have been omitted because use of the equations or computer subroutines 

 does not require a complete description of the means by which they were derived. 



Except for quaking aspen, all site indices are referred to at a base age of 50 

 years. For the user's convenience, computer programs that contain the calculating 

 procedure are presented whenever the calculations required to obtain site index or 

 yield capabilities for a species involve more than the simplest equation. The programs 

 are written in FORTRAN IV. They have been tested on an IBM 360, Model 67 computer and 

 they can be expected to function on any IBM 360 having the minimum of a FORTRAN IV, 

 Level E compiler available. The programing might not always be the most efficient for 

 the IBM 360 because the programs are designed to allow modification to other versions 

 of FORTRAN. These programs have been written as subroutines because it is expected 

 that their use will be implemented through a larger program. 



The user is cautioned that extrapolation of statistically fitted equations beyond 

 the range of the basic data may lead to inaccurate predictions. The probability that 

 this will occur is greater when the equations are more complex. Mistakes in input 

 data, poor selection of site trees, or the sampling of a site quality not represented 

 in the data basic to an equation can prevent the iterative process from reaching a 

 solution. It may well be that this trouble will never be encountered, but it is 

 something of which the user should be aware. 



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