138 The Farm Woodlot 



to that of 65 cubic feet to the acre a year. This increase 

 in yield has been brought about almost entirely by a sys- 

 tematic and intelligent process of thinning. 



The theory of thinning lies in the fact that a tree as a 

 growing organism is governed in its rate of growth and 

 perfection of development by the amount of light, mois- 

 ture and soil fertility it secures. Light is the first and 

 most important factor. A tree responds to light through 

 its leaves just as an animal responds to air through its 

 lungs. Leaves are the lungs of plants and it is through 

 the leaves that most of the wood of a tree is formed* Wood 

 is made up largely of carbon obtained from the air by the 

 leaves in the presence of sunlight. It follows then that 

 increased light produces more leaves, consequently a 

 greater leaf surface, which results in a greater production of 

 wood. A tree growing in dense shade cannot develop as 

 fast as when given a large amount of light. It should be 

 the purpose of every woodlot owner to produce wood as 

 rapidly as possible. As soon as a stand of trees becomes 

 crowded and the trees interfere with one another, some 

 should be removed and a greater amount of light admitted 

 to the remaining ones. The amount of light to admit at 

 any one time is a matter for careful judgment, since height 

 growth is best obtained in a close stand, and a crop of 

 grass must not be allowed to come in and occupy the forest 

 floor. 



To illustrate how largely wood is made up of carbon 

 taken from the air by leaves in the presence of sunlight, 

 let us take as an example a cigar and a piece of wood the 

 same size ; burn the two and compare the amount of ash. 

 The cigar is a product of the leaves of a plant, while the 



