Feb. i6,1914 
Indicator Significance of Vegetation 
399 
taproot, its root system being, therefore, very different from that of 
Kochia vestita. 
The roots of shadscale, although by no means so deep as those of 
Artemisia iridentata , doubtless as a rule penetrate and obtain water 
from a greater depth of soil than do the roots of Kochia. 1 This would 
help to explain the fact that, notwithstanding the more favorable con¬ 
ditions for penetration of water, the deficit during periods of drought of 
moisture available for growth in the second, third, and fourth feet is 
normally greater in shadscale than in Kochia land. 
The moribund appearance in 1912 of the shadscale plants in most of 
the area covered by this association in Tooele Valley points to the con¬ 
clusion that in years of not more than average rainfall the moisture 
supply is inadequate. Thus, in 1912 the moisture available for growth 
had been exhausted to a depth of 4 feet, and the plants had begun to 
shed their leaves before the end of June. Apparently, with the normal 
thickness of stand in this association, the older individual plants can not 
obtain sufficient water to maintain life in all parts of their bodies. The 
branches are in active competition and the plant as a whole remains 
alive only by sacrificing some of its members. The death of some of the 
branches in almost every plant which has passed the seedling stage 
reduces by so much the transpiring surface and results in a proportionate 
economy of the scanty moisture available to each individual. To an 
even greater degree than Artemisia iridentata this plant has the faculty 
of remaining during a great part of the year in a nearly dormant condi¬ 
tion, while retaining some of its foliage. 
Effects of Disturbing Factors: Successions 
The exact stages in the revegetation of shadscale land from which the 
original plant cover has been removed by fire or by the plow remain to 
be worked out. There is evidence, however, that Gutierrezia sarothrae 
forms an important stage in these successions. A large area near the cen¬ 
ter of Tooele Valley is covered with an almost pure growth of this small, 
yellow-flowered plant of the Composite. While a part of this tract was 
probably once occupied by sagebrush, the greater portion occurs in the 
midst of the shadscale belt and has a strongly saline subsoil. 2 
1 Nevertheless, the Atriplex roots do not develop well in a strongly saline subsoil. Thus, at a boring 
where the first foot of the soil contained o.i and the second 0.8 per cent of salts, few living roots were found 
below the depth of 12 inches. 
2 This plant shows marked adaptability to varying soil conditions. In areas having a saline subsoil, 
which were presumably covered originally with shadscale, the plants of Gutierrezia are scattered and 
small and have a superficial root system, while in nonsaline areas, where sagebrush was probably the 
original vegetation, the stand is denser, the plants are larger, and a good taproot is developed. 
