PLxVNTING AND CARE OF TREES 21 



trunk may be best measured directly by calipers at breast height from 

 the ground or indirectly obtained by dividing the circumference by 

 3 (more accurately by ir =3.1416). A number of rough methods 

 of estimating height are given in books on forestry. For example, 

 from a distance equal to several times the length of the tree, the 

 height of a 10 ft. pole beside the trunk or a mark on the trunk 

 of known height may be compared with the height of the whc 

 tree. 



The height to which one can reach may be detennined by trial 

 and this kept in mind as a unit of measure. A piece of paper is 

 fastened to the trunk at this height from the ground. From a 

 distance, with arm fully extended, we measure oif w4th the finger 

 on a lead pencil the height of the paper from the ground which 

 we will imagine to be 7 feet. Using this distance on the pencil 

 as a scale, we continue sighting upward and find that the top of 

 the tree is 8^ units, let us say, from its base. Each unit being 

 7 feet the total height is, therefore, approximately 59^^ feet. Ex- 

 perience has shown that if the distance from which the sights are 

 made is at least three or four times the height of the tree and the 

 arm is kept fully extended during the process of sighting, the re- 

 sults show a fair degree of accuracy. 



The shadow of the tree may be compared w^ith the shadow of an 

 erect pole of known height and the height of the tree computed by 

 the rule of three. A right angle triangle constructed of wood or 

 cardboard with two sides equal may be used as a measure. One 

 of the equal sides is kept vertical by an attached plumb line and 

 sights are made along the long edge from different distances till 

 the top of the tree is just seen above the line of sight. The dis- 

 tance paced to the tree gives the height of its top above the eye. 

 Instead of using a triangle to find the point from which to pace to 

 the tree, German foresters are said to sometimes use a cruder 

 method which consists in bending over with the back to the tree 

 and finding the distance where the top is just visible when viewed 

 with the head between the knees. This method, however, has 

 natural limitations. The last three methods are conditional upon 

 the tree standing upon approximately level ground. 



Instruments for more accurate measurement are on the market 

 under the name of hypsometers. A home-made instrument may 

 readily be constructed which has been found to compare favor- 



