SUMMARY. 127 



relatively shallow-rooted. Almost without exception the major por- 

 tion of the absorbing system lies within the surface 18 inches. A few 

 relicts from earlier successional stages had roots which penetrated 

 somewhat deeper. Many of the roots of tree dominants were found 

 to be superficial. 



The water-content of the soil offers a logical explanation for this 

 community root habit. The duff retards run-off as well as evapora- 

 tion. The trees and shrubs reduce wind movement, lower the tem- 

 perature and evaporation, and consequently greatly reduce water- 

 losses by transpiration. Series of moisture determinations show that 

 the surface 6 inches of soil usually have more available water than the 

 underlying 6 inches, while the third foot is usually much drier than the 

 second. This may be accounted for by the frequent summer showers. 

 Not only are the herbs and shrubs of the forest floor shallow-rooted, 

 but also as a rule the root systems are less extensive in proportion to 

 the transpiring area than is the case with the half-gravel-slide and the 

 gravel-slide plants. 



The root systems of several species growing in two or more dis- 

 tinctly different habitats were studied. It was found that in most 

 cases the root type conformed to the community root habit in which the 

 species was excavated. Thus profound differences, both in root depth 

 and position and number of branches, were determined for most 

 ecads. In general root position conformed strikingly with the distribu- 

 tion of soil moisture. A few stable species were found which showed 

 little or no variation of the root system when grown under different 

 environmental conditions. 



The general characters of the root systems of a species are often as 

 marked and distinctive as are the above-ground vegetative characters. 

 But the root systems of different species of the same genus, while often 

 somewhat similar, may be of entirely different types. 



A knowledge of the position and competition of roots is indispen- 

 sable in explaining the phenomena of succession. Since root position 

 so clearly reflects the moisture conditions of the soil, especially when 

 interpreted in its community relations, a study of the root habits of 

 plants greatly increases our knowledge of the value of various plants 

 in indicating lands of agricultural or non-agricultural value. A knowl- 

 edge of root habits is of further value in solving the problems of the 

 competition of range species and the improvement of the range. 

 Finally, root systems indicate the distribution of soil moisture in 

 various habitats, and thus should aid the forester in selecting sites for 

 reforestation or afforestation. 



