Feb. 16,1914 
Indicator Significance of Vegetation 
383 
surface soil was not high enough to prevent the germination and seedling 
growth of the Artemisia. 
Summary of Physical Conditions. —The observations made in 
Tooele Valley lead to the conclusion that in this area a good stand and 
growth of sagebrush indicates (1) a rather coarse textured, readily 
permeable soil, with low run-off and good underdrainage (water table 
low); (2) a depth of soil of at least 3 feet, in which water can be 
stored and into which the roots of plants may easily penetrate; (3) at 
least 3 feet of soil free from alkali salts in quantity sufficient to injure 
ordinary crop plants. 
Adaptations to the Physical Conditions 
The herbaceous species of the sagebrush association are for the most 
part shallow rooted, and, hence, are dependent upon the moisture of the 
upper soil. The great majority of them grow so rapidly during the 
spring and early summer that they are able to complete their develop¬ 
ment and ripen seed before the water content of the first foot or two of 
the soil has been exhausted to the wilting coefficient. When this occurs, 
they die, at least to the ground. 1 After the middle of July few living 
plants except sagebrush are visible in typical areas of this association. 
The dominant species, Artemisia tridentata (sagebrush) is able to 
continue growth during a longer period. As shown in figure 5 and in 
Plate XLIV, figure 2, it possesses a “generalized” type of roots 2 —i. e., 
a highly developed system of laterals in the upper soil and also a deeply 
penetrating taproot. The former are admirably adapted for securing 
the moisture which penetrates only to a small depth during light rains 
and for which in spring and early summer this plant must compete with 
the numerous associated annual and perennial herbs. By means of its 
taproot the plant can also avail itself of moisture stored at greater 
depths 3 in the readily permeable soils which are preferred by ‘this 
association. 
The great development of superficial lateral roots favors rapid growth 
so long as abundant moisture is present in the upper soil, while the deep 
penetration of the taproot permits the plant to continue growth at a 
slower rate long after most of the herbaceous species of this association 
have withered away. In typical areas of sagebrush vegetation as repre¬ 
sented in Tooele Valley (PI. XLIV, fig. 1) the available moisture is 
probably exhausted before the end of the summer in all depths of soil 
1 They are for the most part" drought escaping ’' rather than " drought enduring.” See Kearney, T. H., 
and Shantz, H. L., The water economy of dry-land crops, U. S. Dept. Agr., Yearbook, 1911, p. 354-357. 
1912. 
2 See Cannon, W. A., The Root Habits of Desert Plants, Washington, p. 87, 1911. (Carnegie Inst., 
Washington, Pub. 131.) 
3 Plate XLIV, figure 2, reproduced from a photograph taken in the vicinity of Nephi, Utah, shows the 
taproot of Artemisia tridentata extending vertically to a depth of over 15 feet. The root penetration of this 
plant under optimum conditions was not studied in Tooele Valley, but it is unlikely that in most of the 
area there occupied by this association the roots reach so great a depth. In this locality the deepest rooting 
plants are doubtless those which grow on the sand hills. 
