Native: Vegetation 
33 
lower altitudes than lodgepole pine, while lodgepole pine flour¬ 
ishes at lower elevations than Engelmann spruce and balsam fir. 
Douglas fir is an associate of both yellow pine and lodgepole pine, 
but usually does not extend far into the lodgepole pine belt. As¬ 
pen, although found from 5,000 feet to timber-line, is best devel¬ 
oped in the lodgepole pine zone. White fir has about the same 
altitudinal limits as lodgepole pine. 
GRASS-STEPPE 
Distribution. —Grass-steppe or a short-grass formation is the 
dominating vegetation over the Great Plains of Colorado, from its 
eastern border up to the foothill base, where it meets a woody 
type of vegetation, which may be thicket or coniferous forest. It 
is almost uninterrupted, except by fringes of broadleaf forests 
along the watercourses, and by fragments of the prairie-grass 
type of vegetation in its eastern portion, represented by bunch- 
grasses, and that vegetation peculiar to sand-hills and blowouts. 
The short-grass type of vegetation, so well exemplified on the 
plains of Colorado, extends from almost the Canadian line to 
southern Texas, and eastward to the prairies (tail-grass forma¬ 
tion) in the central part of the Dakotas, Nebraska and Texas. 
Character of Vegetation .—The two most characteristic grasses 
of the Great Plains are buffalo-grass ( Buchloe dactyloides) , and 
grama-grass ( Bouteloua oligostachya) , shallow-rooted plants, in¬ 
dicating a soil with considerable run-off and little penetration. 
However, there are localities, more or less limited, over which 
these two grasses may appear relatively unimportant, and taller 
forms hold sway. For example, near the mountains, especially on 
a course, non-agricultural soil, which permits a deeper penetra¬ 
tion of water, bushy snakeweed ( Gutierrezia sarothrae ) and com¬ 
mon, small silvery sage ( Artemisia frigida ) are locally important.- 
Again, in eastern Colorado, adjacent to sand-hills, wire-grass (Ar- 
istida longiseta) may cover wide stretches. Moreover, taller her¬ 
baceous plants may seem to dominate during certain seasons. But, 
take it the Great Plains over, the distinctive vegetation is a short- 
grass formation in which buffalo-grass and grama-grass are the 
most important components. 
Climate. —Grass-steppe is a vegetative response to a low, in¬ 
frequent rainfall, the greater percentage (approximately 7 5%) of 
which comes during the growing season, and about 60% of which 
is during the four months June, July, August and September. 
Grass-steppe in Colorado occupies territory with a mean annual 
precipitation ranging from 10 to 20 inches. There is seldom more 
than 50 inches of snow. The average for 13 stations is 26.6 inches. 
