4 MISC. PUBLICATION 257, U. S. DEPT. OF AGRICULTURE 



roots and are thus able to reach deep-lying sources of water in the soil. 

 Others, like the spruce, form a shallow system of fibrous roots which 

 extend in all directions from the base of the tree, and which may, ac- 

 cording to Bindseil (15), extend 30 feet from the base of the stem. 

 Between these two extremes are all gradations and intermediate types. 



The proportion of the root system to the rest of the tree also varies 

 with the species as indicated by Buhler (23), who states that in 2-year- 

 old spruce grown on loam soils in a nursery, the weight of the root 

 system is 25 percent of that of the entire plant; in fir, 45 percent; in 

 pine, 13 percent; in larch, 39 percent; while in the broad-leaved trees 

 the root percentage is much higher, being 61 percent in the beech and 

 about 76 percent in the oak. These specific differences in root systems 

 are probably connected with specific water requirements. 



These specific differences are considered by Hayes and Stoeckeler 

 (92), who tabulate the relative rooting depths of trees 20 to 40 years 

 old on fine- textured soils as follows: 



Deep-rooted (10 to 20 feet in depth): 



Ponderosa pine. 



Hackberry. 



Honeylocust. 



Bur oak. 



Mulberry. 



Osage-orange. 

 Intermediate (5 to 10 feet in depth) : 



Green ash. 



American elm. 



Red cedar. 



Russian-olive. 



Caragana. 



Boxelder. 



Black locust. 

 Shallow-rooted (1 to 5 feet in depth): 



Jack pine. 



Scotch pine. 



Norway spruce. 



White willow. 



Cottonwood. 



Catalpa. 



EFFECT OF THE ENVIRONMENT 



It is possible, however, for the environmental influences mentioned 

 above, which include both the physicochemical and the biotic, or root- 

 competition factors, to cause a pine to have a more widespreading 

 root system than a spruce. Weaver and Kramer (228) have stated: 

 " Although the root habits of a tree are governed, first of all, by the 

 hereditary growth characters of the species, they are often quite as 

 much the product of the environment." 



Roots are living things and tend to grow through the soil in the 

 direction of the materials needed for the life of the tree. Thus, if the 

 soils are becoming dry, the roots tend to grow in the direction of 

 available moisture; if a certain region is waterlogged and lacks air, 

 the roots will grow toward better aerated regions; etc. The type of 

 soil and its compactness also affect the type of root system developed 

 in it, as pointed out by Hayes and Stoeckeler (92). The roots, in 

 other words, show a certain type of "adaptation" to their environ- 

 ment within the hereditary mold. Some species, however, are much 

 more plastic than others and are consequently able to grow in a greater 

 variety of sites. 



