NATURAL HISTORY OF THE FOREST. 157 



the important question of volume development of 

 stands. Hopeless as this would seem at first, it 

 has been accomplished with tolerable success by 

 German foresters, and a good beginning has been 

 made for the species of the United States. 



The general laws which have been deduced 

 from the thousands of measurements made by the 

 Germans are, within limits, applicable to our native 

 species ; they exhibit at least what the possibilities 

 are under good management. 



In the first place, these measurements show that, 

 so far as weight of production is concerned, the 

 same acre produces annually the same weight of dry 

 material, with practically whatever species it may 

 be grown, namely from 4000 to 8000 pounds per 

 acre, according to the quality of the acre (see p. 123). 

 In volume there is, to be sure, a considerable dif- 

 ference, due to the difference in specific weight of 

 the wood of different species, and of the water con- 

 tents ; in other words, the trees with heavy wood 

 would, ceteris paribus, produce less volume per year 

 than the light woods. That the weight of vegetable 

 product should be the same was logically to be 

 expected, since on the same acre the active factors 

 which produce assimilation and the potential energy 

 of the soil remain the same, and the result in prod- 

 uct must be the same. Nearly one-half of this 

 product is represented by foliage and roots, and one- 

 fourth by brush wood and bark, leaving only about 

 three-eighths available as useful wood material. 



