COTTONWOOD IN THE MISSISSIPPI VALLEY. 98 
height and diameter of bottomland trees at different ages. Even 
on fresh, well-drained upland situations, where cottonwood seldom 
occurs naturally, planted trees will easily increase 2 to 3 feet in 
height annually for the first 20 years. 
GROWTH AND YIELD OF STANDS. 
The most important question in considering the growth of a spe- 
cies is, How much wood will it yield per acre? The growth of cot- 
tonwood stands was determined by means of 100 sample plots laid 
off in pure stands of cottonwood on overflow lands in the lower Mis- 
sissippi Valley. 
The growth of stands depends on the growth of the individual 
trees and on the number of trees per acre. Pure stands of cotton- 
wood are open in character. Table 3 shows the average number of 
trees per acre at different ages. It is apparent from this table that 
the rapid growth of individual cottonwoods is to some extent offset 
by the comparatively small number of trees to the acre. At 35 years 
59 trees remain, of which 53 are 14 inches and over in diameter. 
By 40 years the total has diminished to 48, nearly all of which are 
at least 14 inches in diameter. The rapid decrease in number is 
apparent when it is seen that at 10 years there were 699 trees, at 20 
years 163, and at 30 years only 80. (See Pl. IV.) 
Because of the open character of cottonwood stands very heavy 
vields of lumber per acre are rare. By utilizing all trees down to 
14 inches on the stump to a top diameter of 12 inches, it is doubtful 
if even the best pure stands will cut over 40,000 board feet per acre. 
- Yet, considering the early age at which cottonwood reaches mer- 
chantable size, the yield compares favorably with that of such trees 
as white pine and Douglas fir, which, though larger, take a much 
longer time to reach such size. Measurements of a large number of 
plots in the Mississippi River region show that fully stocked pure 
stands yield an average of 31,000 feet board measure in 40 years, 
and that some stands at this age will cut as high as 36,000 feet to 
the acre. 
Table 3 gives the average yields from fully stocked stands of 
.cottonwood at different ages in board feet and cubic feet. The 
average annual yield of a stand is obtained by dividing the total yield 
per acre by the age. From Table 3 it is apparent that the number of 
board feet produced per year is greatest when the stand is about 35 
years old, after which the average annual production gradually falls 
off. Theoretically, therefore, the best time to cut cottonwood is 
when its average annual production begins to decline. As shown 
later, however, other factors may affect the time of cutting. 
