TREE GROWTH AND CLIMATE IN THE UNITED STATES 525 



Under favorable growth conditions loblolly pine, the fastest growing 

 species in this type, will attain a diameter of 24 inches and total height 

 of 111 feet in 100 years. The density in this type is low because the 

 species are relatively intolerant and there is a small amount of avail- 

 able soil moisture. The best estimates show an average density of not 

 more than 75 trees per acre with total yields of approximately 7,000 

 cubic feet per acre. 



Southern Bottom Land Type 



In spite of the long growing season, from nine to eleven months, 

 and the rapid evaporation which this long growing season entails, 

 there is a relatively large amount of available soil moisture on account 

 of the slow run-off. This in turn is due to the fact that the drainage 

 is poor. This type includes the swamp and bottom lands of the southern 

 coastal plain, of which the Dismal Swamp and the Everglades are the 

 most striking examples. The most characteristic species are cypress, 

 tupelo gum, red gum, with some loblolly pine, cottonwood, and ash in 

 association. Diameter, height growth, and yield are all high in this 

 type on the better drained sites ; for example, cottonwood, which 

 never occurs except on the relatively high portions of the swamps 

 immediately adjacent to the river banks, reaches an estimated diameter 

 of 37 inches and a total height of 150 feet in 100 years. Cypress will 

 attain 33 inches in diameter and 119 feet in the same time, while ash 

 will reach 31 inches and 117 feet, and red gum 27 inches and 90 feet. 



Xo satisfactory density figures are in existence and the only yield 

 data are for cottonwood, which shows a total yield of 12,000 cubic 

 feet in 100 years on Quality I sites. Of course these growth and 

 yield figures only apply to the better drained sites. In the wet back 

 swamps where there is more or less water standing all the time, the 

 growth is not nearly so rapid. Too much moisture is of course just 

 as bad as too little, and has approximately the same effect in retarding 

 the growth. 

 Western Yellozv Pine 



In this type western yellow pine is the dominant species, although 

 occasionally Douglas fir, lodgepole pine, and alpine fir do occur. The 

 type is characterized by all qualities of soil, although clay loam is the 

 most common. The growing season is from five to seven months in 

 length ; the precipitation never exceeds 30 inches and may drop off 

 to 20 inches per annum; the evaporation is rapid on account of the 



