2 MISC. PUBLICATION 101, U. S. DEPT. OF AGRICULTURE 
occupied by shrubs in the Western States, but it undoubtedly runs 
into nine figures (102, 120.) There are millions of acres of the 
chaparral types in California alone; the sagebrush formation char- 
acterizes the landscape of vast portions of the Great Basin and the 
Rocky Mountain region generally, while the tremendous wastes of 
the southwestern desert support numerous highly specialized types 
of shrubby plants. On the basis of Shantz and Zon’s natural 
vegetation map of the United States (120, pt. 1, sec. EF’) the areas 
of the five essentially browse types of the West are as follows: 
Square miles 
Sagebrushece 40) lec 3 ANA | BAe ee SE a Be 213, 646 
Creosote bush 2 22.0 SE ee a one rae ane 133, 872 
Piflon-juniper.- 32 - = Ss ee ea Ss eee $29) GL 
Grease wood L2s2 aS aie eee ee ee 19, 551 
Ghaparral! 22925 2 7 Se ee eee oe ee 17, 980 
Totah 2 oe oe te ee 514, 760 
Shrubs frequently grow in pure or nearly pure stands, forming a 
distinct shrubby type of vegetation; even more commonly, however, 
they occur in conspicuous admixture with other plants; for example, 
as an understory in forests or as more or less scattered individuals 
in grass or weed types in parks, on foothills, and on mountain slopes. 
In the mountain regions of the West shrub types are often met with at 
the lower elevations, as on the foothills and lower plateaus, above 
or near timber line, on southerly or easterly slopes, or on burns and in 
alkali basins. In regions of too great aridity, coolness, evaporation, 
or alkalinity to support tree growth shrubby formations are com- 
monly encountered. 
Students of plant distribution and succession are wont to dis- 
regard shrub associations, in favor of trees or grasses, in designating 
climax or permanent types of vegetation, but there are numerous and 
important instances where shrubs constitute a permanent type. 
There is no question as to the stability and permanence of the shrub 
type of vegetation on huge areas of the Western States. 
Harshberger (57), who has made the fullest account of plant dis- 
tribution in North America, discusses over 380 essentially shrub 
formations in the West. ‘These are: 
Sand-hill territory 
Amorpha (leadplant)-Prunus (sand plum)-Ceanothus association, in the sand 
hills. 
Foothill district 
Sage formation. 
Greasewood-Eurotia formation. 
Mountain-mahogany scrub formation. 
Southern. Park mountain district 
Meadow-thicket formation. 
Oak-mountain-mahogany formation (foothill thicket at eastern base of the 
mountains). 
Willow-birch bog formation. 
Rocky hills formation. 
Black Hills area 
Limestone-table-land formation. 
‘Italic numbers in parentheses refer to Literature Cited, p. 180. 
