WATER UTILIZATION BY TREES 5 



Although, according to Cheyney (85), jack pine, which grows in dry, 

 sandy regions, is characterized by a widespreading shallow root system 

 rather than by a deep-rooted system, as might be expected, in general 

 seedlings that survive on more arid sites are more likely to possess a 

 taproot at this early growth stage than seedlings of species growing in 

 more mesophytic conditions, as discussed by Tourney (215, pp. 

 157-165). These same conclusions may be drawn from the work of 

 Holch (101), who grew Quercus macrocarpa Michx., Q. borealis Michx., 

 Hicoria ovata Britt., Tilia americana L., and Juglans nigra L. in 

 three different habitats in southeastern Nebraska. The roots spread 

 much farther than the tops and, in the species mentioned, produced 

 during the first year root systems 5.7, 2.4, 2.5, 1.2, and 4.5 feet deep, 

 respectively, the greater depth and stronger lateral branches being in 

 the drier sites. 



Somewhat similar results are reported by McQuilkin (144) for 

 Pinus rigida Mill, and P. echinata Mill, in a fairly comprehensive 

 series of studies on the root systems of these plants as influenced by 

 age, site, type of soil, aeration, water supply, etc. 



Not until much more information of this sort is at hand for all our 

 economic species will our fundamental silvicultural practices be on a 

 technically sound basis. 



ROOT COMPETITION 



The effect of root competition has been studied by numerous in 

 vestigators, especially in the case of herbaceous plants. Craib (89) 

 carried on. some experiments to show the effect of this factor on the 

 amount of soil moisture available to coniferous trees in New Hamp- 

 shire. Trenches 1 foot wide and 3 feet deep were dug around white 

 pines so as to isolate the soil from root competition of plants in the 

 adjoining quadrats. The amount of available moisture was greatly 

 increased by the elimination of root competition, and in very dry 

 periods two to nine times as much moisture was available in the top 

 6 inches of soil in the trenched quadrats as in the un trenched. The 

 competition comes largely from the herbaceous and shrub flora of the 

 forest floor. Beech has about 50 percent of its roots in the top 35 cm 

 of soil and spruce about 70 percent, according to Dengler (4-6), and 

 most tree species have by far the major portion of their absorbing 

 surfaces in the top 3 feet of soil. The effect of root competition by 

 grasses and other herbaceous plants may, therefore, be very serious; in 

 fact, the severity of the competition between grass roots and tree roots 

 is considered by some authors (169) as the chief reason for the absence 

 of trees on the prairies. Some trees, to be sure, have feeding roots 

 6 feet and more below the surface, but the proportion of roots at this 

 depth is small. 



In his well-known monograph on ecological relations of roots, 

 Weaver (226) touches only incidentally on the root systems of trees, 

 but in a later study (227) he performed an experiment to show the 

 effect on young trees of competition with grasses. Honeylocust, box- 

 elder, green ash, white elm, and silver maple were started from seed 

 and grown for 3 years in the prairie near Lincoln, Nebr. Here grasses 

 (mostly blues terns and Panicum) grow 3 to 6 feet high. Four dif- 

 ferent plots were prepared: In (1) the seedlings competed for water, 

 nutrients, and light; in (2) they were watered; in (3) the grasses were 

 clipped to destroy the light competition; and in (4) a strip of sod 1 



