THE SHELTERWOOD SYSTEM 155 



5. Species not desired in the next crop. 



The aim is to leave thrifty dominant trees of moder- 

 ate size regularly distributed over the area. It is often 

 necessary to leave standing trees with overdeveloped 

 crowns, as well as undesired species, when their removal 

 would open the canopy so much as to induce a growth of 

 weeds and brush before the stand is readv for the seed- 

 cutting. 



The preparatory cutting removes from 25 to 40 per 

 cent, of the trees, which amounts to from 20 to 30 per 

 cent, of the volume. The crown canopy is reduced 20 or 

 25 per cent. The aim is to isolate the trees verv moder- 

 ately, leaving them spaced from 3 to 5 feet between the 

 peripheries of their crowns. 



The number of cuttings needed, the severitv of each, 

 and the aggregate opening made, depend on the follow- 

 ing factors: 



1. Danger from Windfall. — The greater the danger, 

 the more gradual must be the opening. 



2. Character of the Forest Floor. — The thicker the 

 vegetable cover, the heavier the cuttings. The slower 

 the natural processes of decomposition, the heavier the 

 cuttings. 



3. The Character oj Canopy. — The thicker the can- 

 opy, the denser is the shade, and, consequently, the 

 heavier are the openings required. 



4. Height of Canopy. — The higher the canopy, the 

 denser is the shade cast, and hence the larger are the 

 openings required. 



