INTRODUCTION 



How fast do trees grow in height? The answer requires a great deal of detail about 

 the tree's environment and about the tree itself, or some specific growth measure on the 

 tree that indicates the combined effects of all environmental factors and the tree's 

 individual characteristics. Diameter increment is such a measure. It is much more 

 easily measured than height increment, and responds to the same growth determinants. 



Diameter increment, however, is much more responsive to effects of stand stocking 

 than is height increment. Past effects of stocking on height growth relative to diam- 

 eter growth are indicated by the tree's form, as measured by the height/d .b .h . ratio, 

 and by its crown ratio (live crown length/total height). In this report, we seek to 

 develop a prediction equation that relates height increment to concurrent diameter 

 increment, tree height, diameter, crown ratio, and habitat type (Daubenmire and 

 Daubenmire 1968) . 



To use this equation for calculating the height increment component of current 

 volume increment of trees on inventory plots, a computer subroutine is provided in 

 the appendix. For more extended prognoses, the same equation for predicting height 

 increment can be imbedded in a computer model of forest stand development (Stage 1973) . 



For many years Forest Survey in the Intermountain Forest and Range Experiment 

 Station has calculated current volume increment from changes in height computed from 

 diameter increment and diameter. Wright (1961) recommended a similar procedure. Both 

 approaches were derived from a single curve of total height over d.b.h. by determining 

 the differences in the curve height for current d.b.h. and for d.b.h. plus diameter 

 increment. Hence, these approaches assume that all trees of a particular species fol- 

 low height/diameter curves that have the same slope for a given d.b.h. 



Better prediction equations should be possible where data are available from 

 direct measurements of height increment. Prediction equations presented in this report 

 are based on analysis of 1,165 trees felled as part of management planning inventories 

 of the Kaniksu, Coeur d'Alene, St. Joe, and Lewis and Clark National Forests in northern 

 Idaho and western Montana. 



