28 THE PRINCIPLES OF HANDLING WOODLANDS 



principles of classifying trees: First by age, second by 

 size, and third by development of crown and position in 

 the stand. 



Age-Class. — It is customary to classify the trees in a 

 forest in arbitrary age-classes. Usually the range of a 

 single age-class is 20 years. Thus, if the oldest trees are 

 120 years, there would be 6 age-classes, 1-20, 21-40, 

 41-60, 61-80, 81-100, 101-120 years. Sometimes, in 

 our forests, age-classes of 50 years are used. In Europe 

 10-year age-classes may be used, but the 20-year age-class 

 is most common, both here and abroad. 



Size-Class. — In a great deal of forest work it is more 

 convenient to classifv the trees by size than by age. 

 The simplest classification is by inch-diameter groups. 

 Two-inch or 4-inch or other classes are used, according 

 to convenience. In certain work in forest mensuration 

 height-classes are also used. 



Crown-Class. — Trees are classified also with reference 

 to the development of the crowns and their position in 

 the canopy of the forest. If the trees in an even-aged 

 stand are examined, it will be seen that there is a wide 

 variation in the development of the crowns. Some trees 

 are distinctly the leaders, with crowns well developed, 

 and occupy the principal position in the canopy. Other 

 trees, crowded from the side by their more thrifty neigh- 

 bors, lag behind in their growth, are shorter, and have 

 a smaller crown and a smaller diameter than the leaders. 

 Still other trees are entirely overtopped and after a time 

 are killed. Five crown classes are recognized, as shown 



