50 



BULLETIN 1105, U. S. DEPAKTMENT OF AGRICULTURE, 



show the most moisture whei'e there is least herbaceous growth and 

 where the pine seedlings are largest. 



Table 14. — Effect of cutting and herbaceous cover upon soil moisture. 

 Sample Plot 3a. August 30, 1920. 



Location of sampling point. 



Wilting 1 coeffici- 

 ent. 



6 inches. 12 inches 



Available soil 

 moisture. 



6 inches. 12 inches 



Outside fence, grazed: 



Stump patches, sparse vegetation. 



Natural areas, bunch grass 



Inside fence, ungrazed: 



Stump patches, dense vegetation . 



Natural areas, bunch grass 



Per cent. 

 12.0 

 12.2 



10.7 



Per cent. 

 16.8 

 16.9 



1L6 

 11.9 



Per cent. 

 5.0 

 2.8 



1.8 

 6.8 



Per cent. 

 3.8 

 2.5 



1.9 

 4.5 



1 All wilting coefficients in this investigation were determined at the Fort VaUey Experiment Station 

 by the wax-seal method of Briggs and Shantz (2). Oat seedlings were growm in ordinary glass tumblers 

 in a greenhouse. The values given for available soil moisture are the net values after deducting wilting 

 coefficient from total soil moisture. 



Note. — The summer rains in 1920 were below normal, with the result that in many places they pene- 

 trated scarcely below 12 inches. On account of the surface packing due to overgrazing, the stump 

 patches outside were probably most affected. In years of normal rainfall all of the samples would show 

 a considerably higher moisture content, and the 12-inch samples would be higher than those at 6 inches. 



The differences which have been pointed out lead to the following 

 conclusions : 



As to size, the striking superiority of the seedlings on stump patches 

 outside the inclosure is due mainly to the fact that they have but 

 little competition for soil moisture, since the ground is almost bare 

 of other vegetation, even the absorption by tree roots having been 

 eliminated. Organic matter in the surface soil strata resulting from 

 the decay of leaf litter is also a contributing factor. On the other 

 hand, stump patches within the inclosures where no grazing is per- 

 mitted bear seedlings which are distinctly below normal size, be- 

 cause of the fact that in these situations the herbaceous vegetation 

 is much denser and more luxuriant than elsewhere, thus subjecting 

 the pine seedlings to severe competition for soil moisture and in a 

 lesser degree for light. 



In point of numbers, the stump patches are during the first tAvo 

 years after germination distinctly below adjacent natural-grass areas, 

 both inside and outside the inclosure. T\n;iere ffrazine- has been eoins: 

 on this difference is due in a large measure to greater damage by 

 sheep on the stump patches than in the bunch grass, as a result of 

 extremely close grazing in the former situations. Absence of ground 

 cover would also tend to affect germination and early survival ad- 

 versely, for reasons previously explained. Within the inclosure, 

 however, where no grazing damage exists, and where vegetation is 

 denser on the stump areas than elsewhere, the above explanations 

 obviously do not hold. In this case, as in the matter of size, the 

 strikingly inferior results on the stump patches must be attributed 

 to suppression by the dense growth of weeds and grass. Unfortu- 



