36 



The Botanical Survey of Nebraska 



land and shrub habitats we find that the latter, with very few ex- 

 ceptions, has the greater amount, A comparison of that between 

 shrub and forest further illustrates the law of succession deter- 

 mined by Fuller in Illinois and Weaver in Washington, Idaho 

 and Minnesota, that as the xerosere progresses toward the climax 

 stages there is a continuous increase in the water content of the 

 soil. 



Periods when no water was available for plant growth in the 

 first six inches of soil occurred twice in the prairie and scrub ; 

 while the non-available point in the second six inch soil layer was 

 reached three times in the prairie, only once in the scrub, but also 

 once in the forest. 



However, as our knowledge of the greater extent of root sys- 

 tems of prairie plants grows and we find how even seedlings of 

 grasses and trees rapidly reach soil depths greater than a foot, we 

 can more clearly understand why drought in the surface soil 

 layers even through extended intervals is not necessarily fatal. 



The following table shows the total soil moisture at depths of 

 I to 5 feet. 



TABLE 4 



Total Water Content of the Soil in the Prairie, Shrub and Forest 



AT Depths of i to 2, 2 to 3, 3 to 4 and 4 to 5 Feet in the Prairie, 



Shrub and Forest at Peru in 1917 



42 



