98 BULLETIN 1105, U. S. DEPAKTMENT OF AGRICULTURE. 



the brush is first laid on the ground it smothers a portion of the 

 native vegetation. If the cover is dense, grass and other plants may 

 be entirely killed in patches. This may result in conservation of 

 soil moisture; but more often surviving plants in the edges of the 

 cover develop so vigorously that they soon appropriate all the sur- 

 plus moisture. This condition is especially noticeable where the 

 brush is close or where unlopped branches project so as to exclude 

 grazing animals. 



The effects of brush during the first two years, which practically 

 covers the first stage, may be briefly summarized as follows: Con- 

 servation of surface soil moisture under the brush favors germina- 

 tion; young seedlings are protected against wind, frost, and exces- 

 sive isolation, but they are exposed to increased danger from damp- 

 ing-off, excessive shading, smothering, and crushing, and in some 

 cases to injurious competition for soil moisture. The net results vary 

 with local conditions and seasons, but, on the average, the end of the 

 second stage is likely to show fewer seedlings on brush-covered than 

 on open plots. 



In the third and fourth years the needles fall, and the overhead 

 screen is in part transformed into a surface mat. In scattering the 

 cover is lighter and closer to the ground than in other forms of brush 

 disposal. The bare branches, however, still form a light screen. 

 Where the surface mat becomes thick it interferes with germination 

 and induces shallow root development. Where it is not over one-half 

 inch thick, however, it is a distinct aid to germination, especially on 

 soils which have a tendency to dry out quickly at the surface, such as 

 cinders or clays. A heavy fall of needles smothers seedlings. It has 

 been observed that nearly all seedlings directly under the leafy por- 

 tions of a branch are usually killed during the first or early second 

 stage, but that many survive in the small spaces between branches and 

 under the less leafy portions. Once the seedlings are safe from being 

 covered the needle mat is decidedly beneficial in conserving soil 

 moisture by checking evaporation. Herbaceous vegetation, however, 

 is likely to become very luxuriant. The needle-mat stage continues 

 about five years. During the latter part of this period the litter of 

 needles is augmented by fallen twigs. On the whole, this stage seems 

 to retard rather than promote the establishment of seedlings. 



The third and final stage begins from 7 to 10 years after cutting, 

 and continues 8 to 10 years. This period represents a process of ad- 

 vanced disintegration. The needle mat eventually becomes reduced 

 to a thin layer of semidecomposed material suggesting a forest mold. 

 The branches succumb to the action of the dry rot caused by the 

 fungus Lemites sepiaria ^^ and are broken down by snow and grazing 



15 The fungi concerned in the rotting of slash in the Southwest are discussed by W. H. 

 Long, "A new aspect of brush disposal in Arizona and New Mexico," Proc. Soc. Am. For, 

 Vol. X, No. 4, 1915. 



