l8o FORESTRY IN NEW ENGLAND 



the average age, which may be considered as the age of the 

 average sized tree. For example, a stand which has produced 

 forty cords to the acre in thirty years may be expected to produce 

 about one and one-third cords per acre a year, for the next few 

 years. This method of predicting growth is only approximate 

 because the growth of a stand is not uniform throughout its 

 life. During the first part of its Hfe the annual growth would 

 exceed the mean annual growth, but in later years it would be 

 less. 



As a basis of forest management to indicate what different 

 types of forest can produce under various conditions, and at 

 different ages, so-called, yield tables^ are in use. Compara- 

 tively few of these have as yet been constructed in this country, 

 but their construction is one of the most important lines of 

 forestry research open to the forester. These tables are based 

 on the measurements of many stands of a given type at different 

 ages, and express the average volume per acre that can be ex- 

 pected at different ages. Such tables may be "local," if based 

 on stands in a single community, or "general," when the data 

 is secured over a large area, as a whole forest region. It will be 

 readily seen that yield tables, for even-aged stands, not only are 

 more easily made, but are of wider application than those for 

 uneven-aged stands. Since the chief use of yield tables is to 

 predict what forests will produce under favorable circum- 

 stances, they are based usually on the measurements of fully 

 stocked stands, and ' then are called "normal." Often it is 

 impossible in our irregular forests to find acres that are fully 

 stocked, and consequently fractions of acres are measured rather 

 than entire acres which include open areas. Three classes of 

 forests need to be studied for the construction of such yield 

 tables: (a) unthinned pure forests; {b) unthinned mixed 

 forests; (c) thinned stands. Thus far all of the yield tables 

 made in this country have been for the first and second classes, 

 especially for pure forests, and do not indicate what these forests 

 can produce when properly treated. In the future this last (c) 



1 Several yield tables are included in the appendix. 



