A ]\I E R I C A N S Y L V I C U L T U R E 



flexile swaying twigs. In heavy storms Yellow Pine often loses 

 wliol^ branches. White Pine, on the other hand, does not lose its 

 shoots (topshoots) easily, unless they are whipped in the wind 

 by the stiff branches of Black Locust, Beech, ]\[aple. Aspen, etc., 

 forming a superstructure above it. The top shoots of the taller 

 individuals are immune from harm. Thus a tree, once in the lead 

 of its competitors, has a good chance to retain the lead over them. 



IV. Grades of density of cover are: Pressed cover, Close cover, 

 Light cover and Open cover. Xo strict definition of these terms can 

 be given. Obviously the number of stems under pressed conditions 

 is very large, and under open conditions very small. 



Indications of a normal cover are: 



a. Relation between length of crown and length of bole. 



b. Xormal diameter growth and height growth. 



c. Proper participation of the various diameter classes in the 

 volume of wood at hand. The normal participation in a pure, even- 

 aged wood is for the 



1st. Diameter class, 40% of total volume. 

 2nd. Diameter class, 24% of total volume. 

 3rd. Diameter class, 17% of total volume. 

 4th. Diameter class, 12% of total volume. 

 5th. Diameter class, 7% of total volume. 



If cover overhead is too dense, the first diameter class shows 

 over 40% of volume and vice versa. 



V. In nature, the same causes necessarily havo the same result. 

 The causes of timber production are soil and atmospheric food " fall- 

 ing " onto the soil in the shape of sunshine, moisture and air. 

 Hence, whatever the species are, it seems as if the acre of ground, 

 fully stocked, must produce on the annual average the same weight 

 of timber, though not the same volume of timber. Thus, ceteris 

 paribus, species of light specific gravity are the best volume pro- 

 ducers. Since, however, shade-bearing species are better digestors 

 of atmospheric and terrestrial food, the largest growth per acre 

 per annum is obtained from shade bearers and " intermediates " of 

 light weight (Hemlock, Spruce, Fir, Douglas Fir, White Pine, etc.). 



In the virgin forest the annual production of wood fibre is 

 exactly offset by the annual death and decay of wood fibre. The 

 virgin forest is a forest seemingly in economic stagnation. 



VI. The sectional area of a tree usually measured chest high 

 (41/0 feet above ground), inclusive of bark, is the area of the circle 

 corresponding with the diameter measured chest high. 



34 



