286 WOOD AND FOREST. 



cultural system can be applied. Indeed, many of the silvicultural 

 systems involve steady improvement of the forest. 



The pruning of branches is a method of improvement, carrying 

 on the natural method by which trees in a forest clean themselves of 

 their branches. 



Seeds of valuable species are often sowed, when the conditions are 

 proper, in order to introduce a valuable species, just as. brooks and 

 ponds are stocked with fine fish. In general it may be said that im- 

 provement methods are only in their infancy, especially in America. 



