Feb. 16,1914 
Indicator Significance of Vegetation 
393 
of the soil contained about 0.15 per cent of salts, the second 6 inches 
0.36 per cent, and the second foot 1.2 per cent, showed only dead roots 
below the depth of 12 inches. A possible explanation of these circum¬ 
stances would be that in some past period of exceptionally heavy rain¬ 
fall the salt had been washed down to an unusually low depth and that 
the growth of the roots had kept pace. In subsequent years an upward 
movement of the salts would have resulted in the death of the deeper 
roots. 
The total quantity of water available for growth in Kochia land is 
probably less than in any other type of land in the valley. The quan¬ 
tity of organic matter produced is also less, and although the plants 
often remain alive throughout the greater part of the summer the total 
quantity of water transpired is necessarily small. 
Poa sandbergii , the only other abundant species of this association, is 
a shallow-rooted grass, which ripens its seeds and withers to the ground 
early in the summer. It is clearly dependent upon the moisture avail¬ 
able in the surface soil. 
Effects of Disturbing Factors: Successions 
Where Kochia land has been plowed so as to completely destroy the 
original vegetation and subsequently has been abandoned, the reestab¬ 
lishment of the Kochia probably takes place rather slowly. When the 
“breaking" has been less thorough and a few plants have been left alive, 
the reestablishment of the Kochia proceeds more rapidly. The interven¬ 
ing stage of annual weeds or of Gutierrezia, such as occurs when the 
vegetation has been removed from sagebrush land, apparently does not 
follow after breaking on Kochia land. 
Grazing is general in Tooele Valley, where many sheep are wintered. 
Kochia land is especially suitable for pasturage, being relatively level 
and free from spiny shrubs. The Kochia plants themselves are usually 
not much injured by grazing, but the associated grass (Poa sandbergii) 
is eaten to the ground and is often almost wholly eradicated. 
Variations from the Typicae Association 
Kochia with Sagebrush. —As was pointed out above, Artemisia 
iridentata penetrates Kochia areas along drainage channels and in other 
places where the soil-moisture conditions are more favorable and the 
salt content smaller than in typical Kochia land. When associated with 
sagebrush, the plants of Kochia are much larger and more vigorous than 
where this plant occurs in the pure association. 
Kochia with ShadscaeE. —On the lower edge of the Kochia zone 
plants of shadscale appear, scatteringly at first, then in greater numbers, 
until finally the two species are found mingled together in approximately 
equal proportions over large areas. The shadscale, being much the larger 
plant, is alone visible at a short distance, even where it is numerically 
