ROOTS OF A PONDEROSA PINE 



James D. Curtis 



At best a silviculturist has difficulty in deciding whether a tree should be cut or 

 left in a stand. Actually he can see only half the tree- -the half that is above ground. 

 He knows neither the extent nor the condition of the half beneath ground even though it 

 may, to some extent, be revealed by the crown. He uses various criteria to make his 

 decision depending on the species, age, density, composition of the stand, the con- 

 dition of the tree , and the market for forest products . And yet , the condition of the 

 aerial part of the tree depends on the condition and arrangement of the subterranean 

 parts. For mature and overmature stems this disadvantage is not very important, but 

 familiarity with and knowledge of tree root systems in weedings, improvement cuttings, 

 and thinnings enable the silviculturist to gain proficiency in marking and thus leave his 

 stand in a better condition than he would otherwise leave it. 



An obvious deficiency in silvical information about many tree species is a lack of 

 knowledge of the development, arrangement, and functioning of root systems, particu- 

 larly in the 25th to the 75th year age group. This deficiency may be due to the work 

 involved in exposing all the roots of a sizable tree without undue damage. Again, it is 

 virtually impossible to find a "typical" tree. Our knowledge of root systems of middle- 

 aged North American conifers in natural stands is confined, with several notable ex- 

 ceptions (Bemdt and Gibbons 1958; Bishop 1962; Cheyney 1932; Heyward 1933; Horton 

 1958; McQuiMn 1935; Woolsey 1911; Yeager 1935), to windthrown individuals and oth- 

 ers whose root systems have been exposed by soil disturbance caused by land clearing, 

 roadbuilding, and massive or limited sloughing. Windthrown trees are a precarious 

 basis for judging the nature of a species' root habit, but they may provide a clue 

 (Busgen and Munch 1929). 



The causes of tree root variation are the depth and nature of soil and the height 

 of the water table which, in turn, determine (1) the availability of oxygen and moisture, 

 and (2) the frequency and nature of obstructions throu^ which roots cannot pass 

 (Busgen and Miinch 1929; Kramer 1949). Several investigators point out that although a 

 species usually has a typical root system, this trait is by no means consistent (Bemdt 

 and Gibbons 1958; Busgen and Miinch 1929; Horton 1958; Jeffrey 1959; Yeatman 1955). 

 The difficulty arises in knowing when this variation occurs because obviously it can 

 modify silvicultural practice. To guide his choice, the tree marker can observe only 

 surface configurations, soil characteristics, and condition and appearance of the tree. 

 Nevertheless, if he can keep in his mind's eye the general nature of the root system of 

 the species with which he is dealing, he will do a better job of marking. 



^Research forester, Intermountain Forest and Range Experiment Station, Forest 

 Service, U.S. Department of Agriculture , stationed at Boise, Idaho. 



