66 



Yearbook^ of Agriculture 1949 



and snow. Furthermore, isolated indi- 

 vidual shade trees do not have the 

 advantage of gaining additional mois- 

 ture by stopping drifting snow, as do 

 shelterbelt or block plantings. Because 

 of the reduction in annual precipita- 

 tion from east to west in the midcon- 

 tinental section of the United States, 

 there is a corresponding reduction in 

 the choice of usable tree species. Sur- 

 vival and growth are usually poor, even 

 for the hardiest species, where annual 

 precipitation is less than 16 inches in 

 the extreme northern part and 20 

 inches in the more southern part of the 

 Plains States. 



Low winter temperatures can like- 

 wise endanger the survival of trees. 

 Even worse are freezes in early fall and 

 late spring. Consequently, the choice of 

 species becomes more restricted the 

 farther north one goes. 



In the following discussion of trees 

 for the Great Plains, we have separated 

 broadleaf species from the conifers and 

 describe in greater detail the trees that 

 can be used in all parts of the Plains. 



The broadleaf species include the 

 ash, cottonwood, elms, oaks, birch, 

 poplars, and others. 



GREEN ASH, a native species, devel- 

 ops spreading branches and makes a 

 medium-sized, round-topped tree up to 

 50 feet in height. Its trunk may grow 

 1J/2 feet thick. It makes a moderate 

 growth and the light-green foliage, 

 turning golden yellow in autumn, gives 

 dense shade. The greenish flowers de- 

 velop in late spring. Green ash develops 

 best in deep, rich, lowland soil, but it 

 also does well on heavier upland soil. 

 It is one of the best broadleaf trees for 

 streets and yards in the Plains States. It 

 is moderately drought-resistant, but it 

 will stand wet as well as dry sites. Borers 

 damage it, especially on droughty sites. 

 Several relatively unimportant leaf 

 spot diseases and a rust affect it. Green 

 ash is moderately susceptible to cotton 

 root rot. 



White, blue, or red ash are impor- 

 tant locally, principally on the extreme 

 eastern edge of the Plains. 



THE PLAINS COTTONWOOD was wide- 

 ly planted by early settlers. This native 

 tree quickly develops an open crown 

 and it reaches a height of 80 or 90 feet. 

 The trunk gets to be as large as 6 feet 

 in diameter at the base. It affords light 

 shade. Flower catkins appear in early 

 spring before the leaves. The leaves 

 become a colorful yellow in autumn. 

 The trees may attain an age of 60 years 

 or more on the better sites. Although 

 they prefer rich, moist soil and thrive 

 particularly well in the lowlands, they 

 will also grow in drier, sandier loca- 

 tions of the uplands. They do poorly on 

 soils with clay hardpan near the sur- 

 face, and should not be planted on 

 sand dunes. The life of the plains cot- 

 tonwood on such soil is short, usually 

 10 years or less. The tree is susceptible 

 to borers, especially on the drier sites. 

 Poplars and cottonwoods are highly 

 susceptible to cotton root rot. Bacterial 

 limb galls, not uncommon, cause con- 

 siderable branch dying in older trees. 

 Fungus stem cankers are destructive to 

 young trees, especially on unfavorable 

 sites where growth is slow. Leaf rusts 

 are common but of little consequence 

 to thrifty trees. Cottonwoods are sub- 

 ject to attack by gall insects, which 

 make them unsightly but cause little 

 harm. They are moderately drought- 

 resistant when well established on good 

 upland sites. They are also susceptible 

 to chlorosis and grow poorly on alka- 

 line soils. They are mainly usable as 

 farmstead trees. When used for street 

 plantings, only male trees should be 

 selected, to avoid the nuisance from 

 cottony seed. Roots of the cottonwood 

 often clog sewer and drain pipes. The 

 wood is weak and subject to breaking 



