Feb. i6,1914 
Indicator Significance of Vegetation 
385 
ground among the blackened stumps. After a few years Gutierrezia is 
likely to become the dominant plant on these burned-over areas. (PI. 
XLV, fig. 1.) This, in turn, is followed by the sagebrush, which gradu¬ 
ally reestablishes itself. 
In sagebrush land which has been plowed up and subsequently aban¬ 
doned, the removal of the shrubs favors the development of various annual 
and biennial weeds, such as Bromus tectorum , alfilaria (Erodium cicuta- 
rium), pigweeds (species of Amaranthus), Sunflower (. Helianthus annuus ), 
wild tomato (Solanum triflorum ), vervain ( Verbena bracteosa) , etc. As 
time goes on, Gutierrezia sarothrae y a small, much-branched, yellow- 
flowered composite, often becomes established and maintains itself 
for a period which is short or long accordingly as the conditions are 
more or less favorable for the reestablishment of the sagebrush. Sooner 
or later the Artemisia reappears (PI. XLV, fig. 2), and unless fire or 
some other disturbing factor intervenes, the territory is eventually 
reconquered by the original association. (PI. XLV, fig. 3.) 
The succession after either fire or breaking may be shortened, Arte¬ 
misia following immediately after the annual weed stage, without the 
intervention of Gutierrezia. As a rule, however, the succession com¬ 
prises (1) a growth of annual and biennial weeds, (2) a growth of the 
perennial Gutierrezia, and (3) the return of the original sagebrush 
vegetation. 
Grazing does not materially alter the sagebrush vegetation, although 
diminishing the numbers of many of the herbaceous species. Artemisia 
tridentata itself is rarely eaten and is, in fact, benefited by grazing, since 
the plants which compete with it for the soil moisture are thereby 
removed. 
Variations from the Typical Association 
Sagebrush with Kochia and with Shadscale. —Near the lower limit 
of the main area occupied by sagebrush this association comes into con¬ 
tact with the Kochia and shadscale associations, and the dominant species 
of the three associations often grow together in a mixed community. The 
plants of Artemisia which push out farthest into areas occupied by these 
other associations are confined to drainage channels, depressions, and 
the vicinity of animal burrows. In such places the conditions as to 
soil moisture are more favorable and the greater penetration of the 
rain water has leached the salts into lower depths of soil than is generally 
the case in Kochia and shadscale land. But along the frontiers of these 
associations scattered, small, and sickly looking plants of Artemisia 
mingle directly with Kochia or with shadscale. 
Borings made where Artemisia tridentata and A triplex confertifolia grow 
side by side invariably showed the presence of salts in the second, or, 
at the deepest, in the third foot of the soil. (Table VI.) The sagebrush 
roots are unable to penetrate this saline subsoil, and the total quantity 
of water available for the growth of this plant is correspondingly limited. 
