172 FORESTRY IN NEW ENGLAND 



the quality of the soil for any species, and consequently a table 

 showing the average height of trees of different diameters and 

 on different sites furnishes a ready means of determining the 

 relative value of the sites for the species in question. In fact 

 the three quality sites commonly recognized are usually deter- 

 mined by a classification of heights. 



I. Age of Trees. 



The age of a second-growth pine tree and of some other 

 species up to fifty or sixty years can be obtained with fair accu- 

 racy by counting the whorls of branches, since the pine makes but 

 one whorl each year. The buds of winter develop in the spring 

 into branches and leader. Height growth is made entirely 

 at the top. One can only approximate the age of most trees 

 without cutting and counting the rings on the stump. Every 

 fall, in our climate, the growth ceases and the tree remains at 

 rest until spring. When activity in the cambium (the tissue 

 just inside the bark) recommences, large wood cells are made 

 with comparatively thin walls. Throughout the growing season 

 new layers of cells are formed, but as the season advances these 

 cells become smaller and their walls relatively thicker. On 

 account of this difference in structure the wood formed in 

 spring and early summer is lighter colored than that formed at 

 the end of the season. A sharp, well-defined line in most 

 species separates the dark growth of the fall from the light 

 growth of the next spring, and the belt between these dark 

 hues is called the annual ring. In the tropics where there are 

 no well-defined seasons, no distinct rings occur, and the age 

 of trees cannot be ascertained in this way. The distinctness of 

 the rings in trees varies with the texture of the wood. In 

 such woods as the spruce, pine, oak, ash and chestnut the 

 rings are easily distinguishable, although slow growth in some 

 cases may require the use of a magnifying glass. With such 

 fine-grained trees as beech, birch and maple, on the other hand, 

 it is often very difficult to distinguish the rings. In obtaining 

 the age of a tree by counting the rings on the stump it must be 



