SYLVICULTURE. 



species of light specific gravity are the best volume producers. Since, 

 however, shade-bearing species are better digesters of atmospheric 

 and terrestrial food, the largest growth per acre per annum is 

 obtained from shade bearers of light weight (Hemlock, Spruce, Fir. 

 White Pine). 



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 

 (4y 3 feet above ground), inclusive of bark, is the area of the circle 

 corresponding with the diameter measured chest high. 



The sectional area of an acre of forest is the sum total of the 

 sectional areas of the trees standing thereon. It rarely exceeds one- 

 half per cent, of the acreage of the ground, or 218 square feet 

 per acre. 



E. Rotation. 



Under rotation is understood the number of years which a seed- 

 ling requires to reach maturity. For a second growth in America, 

 rotations will vary in length from 60 years to 160 years, according to 

 the species and local conditions. During a rotation a \vood lot may 

 pass through the cleaning stages, thinning stages, the stage of pre- 

 paratory cutting, the seed-cutting stage and the stage of final 

 removal. 



F. Size classes and age classes. 



I. Pinchot adopts the following seven age classes or size classes 

 of trees in his " Primer : " 



a. Seedlings, up to 3 feet high. 



b. Small saplings, from 3 to 10 feet high. 



c. Large saplings, 10 feet high to 4 inches diameter. 



d. Small poles, from 4 inches to 8 inches diameter. 



e. Large poles, from 8 inches to 12 inches diameter. 



f. Standards, from 12 inches to 24 inches diameter. 

 3. Veterans, over 24 inches diameter. 



II. During the sapling stage, the specimens form a thicket; dur- 

 ing the pole stage, they form a polewood; and during the standard 

 and veteran stage, a tree forest. 



III. During the thinning stage (pole stages) of trees in an even- 

 aged wood, the following classes of mess-mates might be distin- 

 guished : 



a. After Schlich, " Dominant," " Dominated," " Suppressed, yet 

 alive," and " Dead." 



b. After Pinchot, " Dominant," " Retarded," and " Overtopped." 



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