10 BULLETIN" 285. U. S. DEPARTMENT OF AGRICULTURE. 



Table 3 shows that in the Lake States, as in the East, yellow 

 birch and sugar maple are the most abundant generally, the chief 

 characteristics that distinguish this part of the northern hardwood 

 forest from the northeastern part being the abundance and importance 

 of basswood, elm, hemlock, and white pine, and the absence of red 

 spruce. Here also, however, some spruce extends down from 

 Canada, in this case white spruce being the more important, espe- 

 cially in Minnesota, and black spruce occurring seldom except in 

 the swamps or "muskegs." 



In Michigan the stand of sugar maple alone exceeds that of all 

 the other northern hardwoods combined, and amounts to more 

 than a quarter of the total hardwood and softwood stand. The 

 maple in Michigan is of better quality than in many parts of New 

 England, but in Wisconsin much of the maple is very defective 

 (PI. II). Maple is not abundant in Minnesota, and is as yet of 

 small commercial value; in fact, the hardwoods as a whole are of 

 relatively small importance in this State. Beech is found in Wis- 

 consin only for a short distance inland from Lake Michigan. Yellow 

 birch is especially abundant and important in Wisconsin, and in 

 Minnesota it is the most abundant of the characteristic northern 

 hardwoods. Black birch is found, but much less abundantly than 

 in southern New England. There is more basswood than elm in 

 Michigan; in Wisconsin they are nearly equal in quantity. "Poplar" 

 (aspens) occupies considerable area in all three States, but by far 

 the largest amount is found in Minnesota. In Michigan and Wis- 

 consin the stands are for the most part too young to be of any com- 

 mercial value. 



FOREST RELATIONSHIPS AND THEIR EFFECT ON COMPOSITION. 



There are two sets of factors which influence the success of trees 

 in the natural forest, and which must be regarded in silviculture: 

 Physical, including soil and climate, and physiological, including 

 aggressiveness in reproduction, tolerance of shade, rate of growth, 

 form, size, longevity, and resistance to injury and disease. To 

 some extent these factors are interactive, and a deficiency in one 

 or several may be offset by a marked superiority in some other. 

 For instance, rapid growth may compensate for intolerance of shade, 

 air moisture for soil poverty, abundance of seed for low fertility, 

 and longevity and resistance to injury for intolerance and ineffectn e 



reduction. It is therefore profitable to consider the factors d 

 or less in combination. Those of tolerance and reproduction are 

 generally the most important in determining the local distribution 

 and abundance of the species. 



Tolerance and reproduction. — Table 4 lists the important species 

 in the northern hardwood forest in the approximate order of their 



