100 
JournaZ of Agricvltural Research 
Vol. XXVIII, No. 2 
an additional key has been prepared arranging the types according to their ap¬ 
proximate carrying capacity. This was based on the average period of the 
time each year that the vegetation can be grazed without injury. 
To aid in the use of the vegetation types, especially to show their range, a 
map was prepared dividing the western part of the United States into 15 regions, 
each having in a general way a similarity in vegetation. A copy of this map, 
together with a list of the types giving their distribution in the various regions, 
follows the text. 
(1) Grama Grass (Bouteloua gracilis (H. B. K.) Lag.).—The grama grass 
type shown by Plate 1, A, is probably the most common and abundant plant 
type throughout the northern and western Great Plains region. It also extends 
westward into the semidesert areas on the high plateaus of New Mexico, Arizona, 
southern Colorado, and southeastern Utah. It is composed of a relatively even 
stand of grama grass, presenting to the eye no other prominent plants, and 
grows in a rather compact fertile loam soil usually known locally as hard or tight 
land. The rainfall over the region occupied by this type is usually between 10 
and 15 inches which penetrates the soil to a depth of 1 to 1} feet. Areas char¬ 
acterized by the grama grass type of vegetation will produce good crops of wheat 
and other small grains only during years of more than normal rainfall. As 
grazing land this type is good, having a carrying capacity of from 20 to 40 head 
of cattle per section. 
(2) Grama Grass and Wheatqrass (Agropyron smithii Rydb.).—The rather 
heavy clay loam soils in the northern Great Plains are mainly vegetated 
by the grama grass and wheatgrass type, which is composed of about equal 
amounts of grama grass and wheatgrass. The heavier the texture of the soil, 
the greater the amount of wheat grass present in the type, while on the lighter 
soils grama grass is dominant. The heavy soil makes crop production doubtful 
in dry years, but relatively heavy in wet years. Considerable native hay is cut 
from this type. It also provides a large amount of excellent grazing, especially 
for cattle and horses. The number of stock that it will graze varies considerably 
according to the density of the vegetation but most of the lands will carry from 
30 to 60 head of cattle per section. 
(3) Grama Grass and Niggerwool (Carex filifolia Nutt.).—A more or less 
equally mixed plant cover of grama grass and niggerwool is a very common type 
in the northern Great Plains. The latter species is characterized by innumerable 
black roots which form a dense tough sod. This type grows in well-drained loam 
soils, frequently where growing conditions are less favorable than for the preced¬ 
ing type owing to shallow or rocky soils, or to a lower precipitation. Crops can 
only be produced on lands supporting this vegetation during exceptionally good 
years. Niggerwool has a very short growing season and produces its growth 
early in the spring. This type is not so good grazing as Type (1), but will usually 
carry from 20 to 40 head of cattle per section. 
(4) Grama Grass, Niggerwool, and Junegrass (Koeleria cristata (L.) 
Pers.).—An even mixture of grama grass and niggerwool containing an open 
stand of Junegrass is a common type in well-drained fertile loam soils of the 
northern Great Plains. A large acreage of this type has been placed under 
cultivation with fair success in all but the drier years. It also provides fair 
grazing, having a carrying capacity ranging from 30 to 60 head of cattle per 
square mile during the average year. 
(5) Grama Grass and Mountain Sage, also known as Fringed Wormwood 
(Artemisia frigida Willd.).—This type, illustrated by Plate 1, B, is composed 
of a relatively pure stand of grama grass with scattered overgrowth of moun¬ 
tain sage. It is found in rather limited areas in the northern Great Plains 
occupying the higher grasslands, mesas, mountains, and valleys, as far south 
