FOREST MENSURATION. 19 



FOREST BIOLOG-Y. 



In order to apply silviculture, to manage a forest crop intelligently, we must first be acquainted, 

 with the biology, the life history, and development of the different species which compose our forest 

 or which we desire to plant. We must kiwwhat conditions of soil, of moisture, of light they 

 require for their best development ; how their growth progresses from the seed to maturity, espe- 

 cially their relative height growth and their light requirement or shade endurance. 



The Division engaged, therefore, in 18S6, a number of botanists to study and report on the 

 life history of our most important forest trees. But it was soon found that such kind of field 

 study from the forester's point of view was foreign to these men, and although a number of inter- 

 esting notes were the result of this first venture into field work, their publication had to be 

 deferred until deficiencies in the information could be supplied. In this way the life history of the 

 white pine, of the four important Southern pines, of the two yellow pines of the Northeastern 

 States, of the spruce and the hemlock, of the juniper, of the bald cypress, and of the white cedar 



were studied. 



But so far only the monographs on the Southern pines and that on the white pine have been 

 perfected far enough to be adjudged satisfactory for publication. The magnificent work on the 

 Southern pines, by Dr. Charles Mohr, published as Bulletin 13, furnished a worthy beginning in 

 this line of investigation. It was the first attempt in the United States of a monographic study 

 from a forestry point of view of the economic, technical, and silvicultural conditions and require- 

 ments of four species of forest trees. 



The monograph on the white pine, being prepared for the press as Bulletin 22 while this report 

 is being written, will in no way be inferior in contents to its predecessor, and several of the other 

 monographs were in a fair way of completion when the writer withdrew from the direction of the 



Division. 



It is upon the basis of such knowledge as these life-histories bring that the forester is enabled 



to apply silvicultural principles in the management of his crop. 



In order to apply principles of forest economy he needs more; he must know the capacity of 

 the species for production and the rate of growth in volume. Another line of work, therefore, is 

 necessary to establish this capacity of production by measurements. 



FOREST MENSURATION. 



The forest crop differs from all other crops, and forestry differs from all other industries of 

 production in two ways. There is, first, no definite period when the crop can be said to be mature, 

 as in the case of agricultural products; it consists of annual accumulations, which are allowed 

 to continue until the individual trees attain either a useful or a profitable size; and, secondly, to 

 attain such size a long time, and with different species and conditions, a variable time is needed. 

 Thus, for firewood production a growth of fifteen to twenty-five years might suffice, while for good 

 lumber production not less than seventy-five to one hundred years and more are needed. This 

 indefiniteness of the time of maturity and the unusually long period of production during which 

 the crop has to grow predicate peculiar business arrangements, entirely different from those 

 prevailing in other industries if forest growing is to be carried on as a financial business, and so 

 necessitate to a greater extent than with any other a full knowledge of the progress of the crop. 



Tree measurements, especially measurements of the rate of growth of single trees and of whole 

 stands of trees, furnish the basis for determining the question when under given conditions the 

 useful or the profitable sizes may be expected to be attained, and also the question of quantitative 



production. I 



The Division has therefore for some time, as opportunity, men, and money were at its disposal, 

 carried on measurements of the rate of growth of certain species, especially of the important 



conifers. 



In the forthcoming monograph on the white pine a comprehensive statement of the growth 

 of this most important timber tree, based on the analysis of nearly 700 trees from many localities 

 will be found, which will show that this species is capable of producing, under proper management, 

 larger amounts of valuable material in a shorter time than any of the European species. 



To establish the amounts which a species can produce in different lengths of time is a much 



