166 PRINCIPLES OF AMERICAN FORESTRY. 



and vigorously from sprouts, and continues to do so for 

 a long period of years, it is probable that such a plantation 

 will last indefinitely. 



Willow wood makes good summer fuel, and as a fence- 

 post, when the bark is removed and the wood well cured, 

 it is quite satisfactory, and will last in the soil about seven 

 years. It is also good for poles when peeled and dried. 



The Common Cottonwood on very rich soil will prob- 

 ably yield from five to seven cords of firewood per acre 

 per year. 



DIAMETER GROWTH OF SOME MINNESOTA TREES. 



Cottonwood 1 inch in 1.4 years 



Norway Spruce 1 inch in 2. 5 years 



Silver Maple 1 inch in 2.7 years 



White Willow 1 inch in 2.8 years 



Basswood 1 inch in 4.5 years 



Sugar Maple 1 inch in 6.6 years 



White Elm 1 inch in 6.8 years 



Bur Oak 1 inch in 8.5 years 



The height growth of Silver Maple and White Willow 

 is about two feet per year, Norway Spruce one foot per 

 year. Bur Oak averaging thirty feet in height makes 

 an average growth of about .55 foot per year, while the 

 rate of height growth of the first twenty feet of market- 

 able cordwood is about one foot in 1.5 y c ars. The height 

 growth of Cottonwood varies from two to eight feet per 

 year. A fifteen-year-old Cottonwood will often grow 

 in height three feet per year. Black Spruce has shown 

 a diameter growth of one inch in 14.7 years, and a height 

 growth of one foot in 2.3 years. 



