the number observed on the laterals of neighboring trees, was much greater than that 

 of other tree roots. A similar situation was recorded in the Lake States where, out of 

 a total of 33,829 inches of rootlets in a square yard, more than half, or 18,879, were 

 other than tree roots (Cheyney 1929). Elimination of this competition might have a 

 pronounced effect on growth of the stand. A correlation between the amount of this 

 ground cover and diameter growth of the stand above it was found in preliminary 

 studies in Oregon.^ 



The tenacity for life of trees is well known (Kramer 1949), but it is illustrated 

 quite forcefully by this tree. The root system described here was exposed and partly 

 eliminated in 1950; only the forked taproot and some sinker roots remained. In the 10 

 years since excavation, radial growth has been only 0.15 inch compared to 1.0 inch 

 during the 10 years prior to excavation. Although the crown had an unhealthy appear- 

 ance for several years, the crown color and annual height growth now appear to be 

 normal. 



Inasmuch as ponderosa pine is considered a species whose root habits are fixed 

 by heritability (Kramer 1949), some silvicultural guides can be noted for consideration. 



1. Many main laterals are close to the surface and can be injured, even severed, 

 by surface fires and logging activity. 



2. The root system extends over an area several times the size of the projected 

 crown. For 18 eastern hardwood trees (17 to 104 years old) this ratio was 4.5 to 

 1 (Stout 1956). For this ponderosa pine it was 5.4 to 1. Competition may there- 

 fore be greater beneath ground than above it because root systems have more over- 

 lapping than crowns. Thinning could decrease this competition. 



3. Because the greatest concentration of secondary laterals is within a radius of 

 10 feet of the bole, and because all the sinker roots are close to the stem (on this tree, 

 about 3 feet from it), thinning near selected crop trees should produce the greatest 

 benefit. This effect of release in terms of diameter growth has been demonstrated for 

 central Idaho (Curtis 1952). 



4. Root grafting can be lessened by thinning, but this would be entirely on a 

 chance basis. Any benefit to uncut trees would depend on the respective sizes of the 

 trees cut and left. 



5. Ponderosa pine is recognized as an inherently taprooted species, but it can 

 also have sinker roots close to the trunk. 



~ Correspondence with E. L. Mowat, formerly with the Pacific Northwest 

 Forest and Range Experiment Station, Bend, Oregon. 



7 



