REPRODUCTION OF WESTERN YELLOW PINE. 137 



the seed supply is deficient. Occasionally a good seed crop is wasted 

 because of deficient or irregular summer rains. Drought in Septem- 

 ber and October sometimes causes heavy losses; frost-heaving usually 

 takes a large toll: but in average years more seedlings die during the 

 drought of June and early July than during all the remaining portion 

 of the year. 



SOIL. 



Next to climate soil is the most important natural factor. With 

 possibly a few exceptions, none of the soils within the climatic zone 

 of yellow pine in this region contain chemical elements inimical to 

 the reproduction of the species. Reproduction seems to be affected 

 most by the physical condition of the soil, as determined by the pro- 

 portion of sand or gravel which it contains. Where the soil is 

 sandy or gravelly reproduction is seldom a matter of serious concern. 

 Clay soils, on the other hand, are unfavorable to reproduction. Clay 

 is rendered more favorable by the admixture of large proportions of 

 gravel or stones. 



HERBACEOUS VEGETATION. 



Herbaceous vegetation favors germination and protects young 

 seedlings against excessive insolation, winterkilling, and frost-heav- 

 ing: but after the first year these benefits are counterbalanced by the 

 unfavorable effects of root competition and shade. This condition 

 manifests itself in slow growth as well as in a high rate of mortality. 

 Reproduction will usually succeed despite competition from the roots 

 of herbaceous plants, provided that the latter do not attain abnormal 

 density or luxuriance. Such a condition is likely to obtain on the 

 richest soils unless the grass and weeds are held in check. Complete 

 eradication of herbaceous vegetation is not considered necessary, and 

 is distinctly undesirable if accompanied by packing of the soil as in 

 overgrazing, or removal of the loamy surface layer as in deep plow- 

 ing. Although special methods of shallow cultivation might be ex- 

 pected to yield superior results, they are not considered necessary or 

 economically feasible in the present stage of forest practice. Under 

 present conditions properly regulated grazing appears to be the most 

 practical means of controlling herbaceous vegetation. 



CUTTING. 



Forest cover assists germination by shading the soil and protects 

 young seedlings against excessive insolation, wind, and frost; but 

 these benefits may later be offset by injurious effects of root com- 

 petition and shade. Excessive shade is limited to a zone which 

 lies well within the crown projections on the south side of a tree or 

 group, but extends to the north a distance equal to about one-third 



