SURFACE COVEEING. 9 



stocked ever since. A large part is in heavy brush, and consequently 

 not as productive as it would otherwise be. A few head of stock have 

 been allowed in the 590-acre pasture since it was fenced, but the large 

 area has had no stock upon it since it was inclosed except an occa- 

 sional stray. The pastures P., R., and MacB. have been handled by 

 their owners very much as their judgments dictated, a record being 

 kept in all cases of just what treatment each pasture received. 



SURFACE COVERING. 



The accumulation of dead herbage upon the surface of the soil of 

 the area takes place very slowly. When the growth first dries up in 

 the fall after a good rainy season there is an accumulation of, perhaps, 

 a thousand pounds of dry matter to the acre. This is enough to make 

 a big fire if ignited shortly after the dry season sets in. If left upon 

 the ground for one year in this climate, however, it largely disappears, 

 from the action of wind and weather, so that the accumulation, while 

 surely taking place from year to year, is very slow. In this inclosure 

 after six } T ears of protection there is in no portion of it a complete 

 ground cover during the entire year. There is, it is true, at the close 

 of the rainy season grass two feet or more high in some places, but, as 

 is characteristic of desert vegetation, it is thin and largely disappears 

 before the next season. In the lower portion of the field, where the 

 annual grasses predominate, the accumulation is next to nothing, 

 but it gradually increases toward the higher level and is most abun- 

 dant in the extreme southern portion of the inclosure. (See PL IV, 

 fig. 2.) The occurrence of a dry year largely obliterates any cover 

 that may have accumulated during the previous season. In short, 

 even after six years of protection there is now in the lower portion of 

 the field practically no ground cover, and in all probability there 

 never has been any. In the upper portion, while the growth increases 

 under protection, there is yet only about half a cover on the ground 

 during the entire year. In the upper country, at an altitude of 3,500 

 feet and upward, a large accumulation of dead herbage can be kept 

 upon the ground under a good system of management, as is being 

 done in some private and cooperative pastures in the region now, 

 but below this altitude the ground cover is not a factor of much 

 consequence, for the grasses are mostly annual. Of course, upon 

 the swales which receive flood waters the galleta and other grasses 

 make a large growth and protect the surface, but such areas do not 

 occur in the inclosures here described. 



It will be seen that the matter of growth is one of distribution of 

 moisture, which is influenced by altitude. As stated elsewhere, the 

 rainfall quoted in this paper is taken in the 204-acre pasture. This 

 point probably receives more rainfall than any portion of the large 

 inclosure, the precipitation decreasing gradually northward until one 



177 



