﻿COTTONWOOD IN THE MISSISSIPPI VALLEY. 21 



lower land was under water. This indirect influence of topography 

 accounts for much of the variation in the character of occurrence of 

 cottonwood in this mixed stand. 



If the cottonwood is well represented in such a mixed stand, there 

 is often almost the appearance of a well-defined two-storied forest, 

 in which the more shade-enduring species, such as elm, sycamore, ash, 

 hackberry, or oak, are partially overtopped by the much faster 

 growing cottonwood. By the fortieth or fiftieth year, however, the 

 stand has usually opened enough to give the associate species room 

 for growth. During the next 50 years these gradually fill in the 

 space left vacant by the death of the cottonwoods. At the age of 

 100 years such stands may contain less than half a dozen large cot-, 

 tonwoods to the acre. 



A pure stand of cottonwoods develops in a similar manner into a 

 mixed stand as the trees reach maturity. In fact, during the 

 early life o_f the pure cottonwood stands there is often an under- 

 story of small sycamore, ash, elm, maple, and other species, which 

 upon examination will generally show the same age as the cotton- 

 woods. These associates, gradually augmented by others that come 

 in as cottonwoods die, ultimately occupy the ground to the exclusion 

 of the latter. 



COTTONWOOD- WILLOW STANDS. 



In the Mississippi Valley cottonwood is frequently associated with 

 various willows, which compete with it in occupying newly made 

 lands and bars. Black willow (Salix nigra Marsh.) is the principal 

 associate in the lower valley, while in the north the almondleaf or 

 peachleaf willow (Salix amygdaloides Anderss.) appears to be more 

 common. The latter, together with the small longleaf or sandbar 

 willow (Salix fluviatilis Nutt.), which is common throughout 

 the whole region, seems to appropriate nearly all the available 

 open areas along the upper river, affording very little chance 

 for the reproduction of cottonwood, which apparently seeds some- 

 what later. CottonWood-willow stands, therefore, are infrequent 

 in the north and usually contain a very small proportion of cotton- 

 wood. They are, however, comparatively common in the lower val- 

 ley. Here the black willow and cottonwood seem to grow on more 

 even terms, and both species make almost equally rapid growth for 

 the first 20 to 25 years. The cottonwood, however, continues to 

 develop, and on many situations may ultimately crowd the willow 

 out of the stand. Since, however, the latter seems to be better adapted 

 to poorly drained land, it is not uncommon to find it crowding out 

 the cottonwood on wet, mucky soils. The cottonwood-willow stands 

 are therefore of a very temporary character, few being over 30 years 



