40 FARM rOEESTRY 



long, clear trunk is finally produced. The succeeding layers 

 of annual rings laid on about the tree will cover over the 

 wound and in a few years there will be nothing to show that 

 a branch ever grew at that point. The branches, however, 

 will remain concealed in the tree and will form the knots that 

 appear when the trunk is sawed into boards. 



During this period the tree grows faster in height than at 

 any other time, and before the large pole stage is completed 

 they will have nearly reached their total height. There is a limit 

 to the height to which trees will grow. Some species naturally 

 grow taller than others, but with every species there is a limit 

 beyond which the moisture from the soil cannot be raised. 

 When this point has been about reached there will be little 

 additional height growth. 



(c) Period of Rapid Diameter Increase. — After the trees 

 have passed the period of most rapid height growth begins 

 the period of rapid diameter increase. The diameter at first 

 small has increased gradually as the trees have developed 

 until with the completion of the rapid height growth the growth 

 energy of the trees becomes concentrated in the production 

 of wood material, and wide annual rings result. 



Owing to the long, clean trunks that have resulted from 

 the rapid height growth and to the shade caused by the trees 

 growing closely together, the diameter growth put on annually 

 during this stage is of clear wood, and the trees increase 

 rapidly in value for lumber. It is the period of the greatest 

 vigor in the life of the trees. Seed production becomes very 

 large. The crowns of the trees become thicker and the ground 

 beneath the trees is shaded more than during the other periods. 

 Having reached their total height the tops of the cfowns are 

 no longer able to push upward, but the side branches begin to 

 grow and strive to reach the same height as the tops. The 

 crowns of the trees lose the more or less conical form which 

 they have had up to this time and begin to flatten out. Because 

 of this sidewise growth the competition between the trees 



