208 



FORESTRY AND IRRIGATION 



May 



assistance in directing logging opera- 

 tions. In taking stem analysis the men 

 need to have the trees felled and cut into 

 logs. For this reason they follow up the 

 loggers at work whenever possible, al- 

 though sometimes they have to cut and 

 section the trees for themselves. First 

 they count and measure the rings of 

 annual growth on the stump or the butt 

 log to learn the age of the tree and its 

 rate of growth in each decade of its life. 

 Sometimes, especially in hardwoods, the 



the contents of an average tree and mul- 

 tiplying by the number of trees ascer- 

 tained from the surveys. 



The mass of wood which a tree adds 

 to its bulk during any period of its life 

 may, for practical purposes, be consid- 

 ered as a hollow truncated cone. The 

 volume of this conical tube of wood may 

 be obtained by calculating the volume 

 of a solid truncated cone of the same 

 dimensions and subtracting from it the 

 volume of the similar interior figure 



FOREST RKSERVE WORK IN THE ROCKIES. 



rings are so closely crowded that a lens 

 must be employed to distinguish them. 

 The height of the stump, length of 

 each log, and the length of top added 

 together give the height of the tree. 

 Diameters are measured at each place 

 where the trunk is sawed through, and 

 the thickness of the bark is noted, so 

 that a vertical median section of the tree 

 could be drawn to scale if necessary, and 

 the actual quantity of wood in the trunk 

 can be closely calculated. From these 

 figures the amount of wood in the whole 

 forest can be estimated by calculating 



whose base is measured on the stump 

 by the annual rings extending from the 

 heart of the tree to the inner side or 

 beginning of the growth period under 

 consideration. 



Thus it may be ascertained at what 

 year of its life the tree ceases to pay 

 good interest, in wood, on the value of 

 the space it occupies. It should not be 

 allowed to stand after reaching that 

 age, and it may be gainful to cut it 

 sooner under some conditions. In this 

 way the plan can name the diameter 

 below which trees should not be cut, in 



