24 Forestry Quarterly. 



tables for our different species and types on different quality- 

 sites these rules could be easily deduced after we had made a 

 careful analysis of the stand. Unfortunately, we do not have 

 many normal yield tables at present, and temporarily at least we 

 must usually construct for ourselves, rough ones, or substi- 

 tutes for them. Since the common methods for constructing 

 yield tables require more time and opportunities than is commonly 

 to be had by forest officers in charge of small timber sales, the 

 following method is offered; developed from a suggestion in 

 "Forest Working Plans" by D'Arcy. 



Method of Regulation. 



To construct our picture of a normal forest of a particular 

 type and site quality, first, from measurements on the whole tract 

 or on sample plots with the aid of which an estimate is made for 

 the whole, we determine the actual number of trees in each 

 diameter class. The age of standing trees is obtained only with 

 great difficulty, unless one has a record of their planting. The 

 diameter of a dominant tree is roughly proportionate to its age. 

 For practical purposes, we shall substitute diameter classes for 

 age classes. Instead, then, of regulating age classes we will aim 

 to regulate diameter classes, since practically it will amount to 

 nearly the same thing. The trees may be divided either into inch 

 classes or, more usually, into classes comprising several inches. 

 But a knowledge of the actual number of trees in each diameter 

 class is of slight value, except in estimating the volume of the 

 stand, unless we have some means of comparing this data 

 with the normal number of trees in each diameter class. 

 As we have no known normal stands with which to make 

 comparison we are forced to construct them theoretically 

 This may be done as follows : the first step is to determine the 

 average horizontal croiun-spread of average dominant trees of 

 each diameter class. The field work may be done by sighting 

 along a plumb line at several points on the margin of the crown, 

 placing sticks or surveying pins in the ground to mark the 

 crown's projection ; after which measurements of the ground area 

 in square feet is computed. It is suggested that a curve be drawn, 

 from which a table of crown-spread may be prepared. If such a 

 table is prepared in advance for different types on three or more 



