16 BULLETIN 2S5, U. S. DEPARTMENT OF AGRICULTURE. 



are an important element of fertility in these soils. The northern 

 hardwoods are not confined to rich soils, however. They often 

 thrive on dry or on very shallow soils, but in each case there must 

 be some compensating factor. A shallow soil must be moist, for 

 example, and a dry one deep. In the lower peninsula of Michigan 

 maple, beech, elm, and basswood grow well near the shore of Lake 

 Michigan on deep, dry, fine sand of low agricultural value, while in 

 the eastern part of the State, adjacent to Lake Huron, they are 

 largely replaced on sandy soils by pines or by dry-land hardwoods, 

 principally oaks. The compensating factor here is probably ah 

 humidity due to the prevalence of moist winds from Lake Michigan. 

 Lender these conditions the growth is more rapid than on heavier, 

 more fertile soil, no farther north, in Wisconsin. Beech is the least 

 exacting species with reference to soil moisture and quality. In 

 Ohio * it grows well in limestone soils in mixture with white oak, red 

 oak, hickory, and white ash, and also on well-drained sandy clay 

 moraines with white oak and hickory. It is rather sensitive to 

 changes in the ground-water level through draining, however, as well 

 as by the opening up of the forest crown cover. White elm, bass- 

 wood, sugar maple, and ash, though apparently less sensitive to such 

 changes, are somewhat more exacting, and in dry climates require a 

 larger amount of soil moisture for their best growth. 



The species differ in the ability of their root systems to adapt them- 

 selves to soils of different depths and moisture content, but as yet 

 little is known of their capacities in this respect. The soil conditions 

 in which they are found indicate that probably the root systems of 

 sugar maple and yellow birch are the least and those of beech, bass- 

 wood, and elm the best adapted to draw moisture from a deep but 

 only slightly moist soil. Where the soil and air humidity are ample, 

 the tendency of all the species is in the direction of shallow-rootedness, 

 and vice versa. 



FORM. 



Tables 50 to 53 (Appendix) show the taper of trees of different 

 species and size, and Tables 5 and 6 give the comparative lengths 

 and breadths of crown of beech, sugar maple, yellow birch, and bass- 

 wood trees. These figures are average measurements of the crowns 

 of forest trees felled to obtain the growth measurements given in 

 Tables 7 to 9, together with the measurements of the sample trees 

 from the second-growth plots described on pages 21 to 27. No regu- 

 lar variation between crown classes was distinguishable, but prac- 

 tically all the trees measured belonged to the upper crown classes. 

 Both the length and the breadth of the crowns are greatest in the 

 most tolerant and smallest in the least tolerant species, though this 



1 O. F. Baker, in "The forest problem in arich agricultural county of Ohio," Forestry Quarterly, vol. 1. 

 No. 2, pp. 138-100 (1908). 



