CHAPTER VI 



TIMBER 



THE kind of timber which is required, and the class which the 

 land will produce, are the two chief points to be . borne in 

 mind when deciding upon the planting of a wood. 



Before considering the characters of the timber, however, the 

 chief terms used in describing these must be explained. 



Annual rings. In most species of trees, a cross section of the 

 trunk reveals the fact that it is composed of a number of concentric 

 rings, formed alternately of dark and light coloured wood. Each 

 pair of rings constitutes one year's growth, and is termed an 

 " annual ring." Spring wood is the light-coloured portion. It is 

 less dense, and it contains larger vessels necessary for the sap to rise 

 in spring when the buds are opening. Summer wood is the dark- 

 coloured portion : it is more dense and of higher specific gravit}-. 



Uniform rings are important in determining the quality of the 

 timber. The breadth is usually governed by the extent to which 

 the crown of the tree is allowed to grow, and it is even possible to 

 trace the periods at which a high wood has been thinned, by the 

 increased breadth of the annual rings. Each thinning allows an 

 increased amount of light and air, and consequently an increase in 

 the size of the crown. The result is an increase in the breadth of 

 the annual ring during the following year. This is continued each 

 year, until the struggle for existence is increased by the restriction 

 due to the growth of the canopy.' Consequently, frequent and sparse 

 thinnings (see Chapter VII) are necessary to ensure uniform rings 

 and, therefore, the best quality of timber. 



Heart-wood (duramen) is the term applied to the inner, and 

 therefore the older, annual rings. This portion no longer contri- 

 butes to the vital functions of the tree, beyond the fact that it acts as 

 a support to the crown. In the heart-wood, the colour is usually 



