112 



BULLETIN 1105, U. S. DEPARTMENT OF AGRICULTURE. 



have been left unburned, when rotted down leave an inch or more 

 of mold on the surface of the soil and give a dark color to the soil to a 

 depth of 2 to 3 inches. This stage of composition is not reached 

 until from 15 to 20 years have elapsed. If herbaceous vegetation 

 is kept down by grazing, these spots favor the establishment and 

 rapid growth of seedlings. As a means of permanently increasing 

 the humus content of the soil, however, brush is ineffective, because 

 it reaches only the surface layers, where the nitrates resulting from 

 decomposition are rapidly dissipated by the dry atmosphere. The 

 greatest objection to deep layers of brush, aside from the fire 

 danger, is that during the first 15 or 20 years after cutting, which 

 is the normal reproduction period, they hinder rather than favor 

 reproduction. 



Table 26. — Relation of brush and (jronnd cover to soil moisture, 1920. 



Location. 



Wilting coefficient, 

 at— 



Available soil mois- 

 ture at — 





6 inches. 



12 inches. 



6 inches. 



12 inches. 



Fort Valley, July 9: 



\ 13.1 

 I 13.1 

 | 10.7 



15.4 

 15.4 

 11.9 



Per cent. 

 ( -1.0 

 \ 1-7 



r -o.4 



0.6 



I 2.7 



f -0.7 

 \ -0.3 



Per cent. 

 -1.2 





4.6 



Fort Valley, Oct. 6: 



3.1 





5.2 



Tree top — 



Litter 2 to 3 inches l ; 



3.0 





0.9 



Sample plot 3, Oct. 9: 



0.1 





1.5 







i Mat of needles about 2 feet in diameter; grass in edges. 



2 Sparse vegetation, but soil permeated by network of roots from group of trees 50 feet distant. 



The foregoing data lead to the general deduction that on areas 

 bearing a dense, luxuriant growth of herbaceous vegetation, espe- 

 cially tall grasses, brush in any form is detrimental to pine reproduc- 

 tion; but that on clay soils, if the herbaceous cover is light or can 

 be held in check by grazing, brush cover is beneficial. On steep 

 slopes control of erosion may be an additional reason for leaving 

 the brush. Assuming, therefore, that under certain conditions it is 

 more desirable to leave the brush than to burn it, we should know 

 something of the relative advantages of the methods which do not 

 involve burning. 



Comparison of scattering, pulling tops, and lopping. — Data giv- 

 ing a direct comparison between scattering, pulling tops, and lop- 

 ping are not so complete as could be desired. Scattering has not 

 been practiced to any appreciable extent on the Coconino and Tusa- 

 yan National Forests 19 and has rarely been executed in accordance 



19 The standard practice on the Coconino and Tusayan is pulling tops, except on fire 

 lines or in places of great fire danger, where piling and burning is practiced. 



