TREE GROWTH AND CLIMATE IN THE UNITED STATES 523 



60 aspen trees per acre in a rotation of 100 years on Quality I sites. 

 The density for northern hardwoods is estimated to be 275 trees per 

 acre at 100 years. In spite of the slightly longer growing season 

 aspen seems to be the one species which makes much more rapid 

 diameter and height growth than is attained in the spruce type. Its 

 diameter and height in 100 years are estimated to be 23 inches and 89 

 feet, respectively. Sugar maple in the same length of time will attain 

 12 inches and 75 feet, yellow birch 12 inches and 74 feet, and the 

 average for the Vermont hardwoods is estimated to be 10 inches and 

 85 feet. 



White Pine Type 



The white pine type includes the sandy soils which are too dry for 

 the growth of northern hardwoods and occurs in New England, New 

 York, and the Lake States. White pine is the dominant species, 

 although beech, birch, maple, red oak, and ash are often found 

 occurring in association with white pine. On the drier sites, especially 

 in the Lake States, red pine and jack pine are also found in this type. 

 Climatically it is characterized by a growing season from four to six 

 months in length; total annual precipitation 30 to 45 inches, medium 

 run-ofif and evaporation. In spite of the rapid drainage of the sandy 

 soils the gentle slopes tend to counterbalance the openness of the soil. 

 Summing up, there is unquestionably less available moisture for tree 

 growth in this type than in the hardwood type, but unfortunately our 

 records do not permit us to measure this absolutely ; a growing season 

 of fair length permits of rapid diameter and height growth. 



White pine attains in 100 years on Quality I sites an average 

 diameter of 20 inches and total height of 113 feet, while red pine in 

 the same length of time will reach 24 inches and a total height of 101 

 feet. Yield tables for white pine show that the best sites have a 

 density of 154 trees per acre in 100 years and will yield 14,700 cubic 

 feet without thinning. 



Southern Hardzvood Types (Cove-Slope-Ridge) 



Climatically the southern hardwood types come next because their 

 characteristics are very similar to the southern extension of the white 

 pine type. However, the total annual precipitation is greater, the 

 run-off more rapid on account of the open winter, and the evaporation 

 considerably greater by reason of the longer growing season which 

 covers from five to seven months. Unfortunately it is not possible 



