20 A PROTECTED STOCK EANGE IN ARIZONA. 



In the production of the two crops of feed which we have in the 

 region of the Coronado National Forest two seasons of rainfall con- 

 tribute. The season which produces the spring crop is much more 

 indefinite than the one producing the summer crop and the crops 

 themselves are very different. The spring feed consists of weedy 

 annuals, and the summer feed of grasses, both annual and perennial. 



The winter rainy season, as it is usually called, may begin as early 

 as October and may last through April, or it may be foreshortened 

 at either end and even almost disappear at times. The summer 

 rainy season, on the other hand, is short, commonly better distributed, 

 and occurs in July, August, and September. In the column in 

 Table I showing rainfall, that recorded under the spring season fell 

 between October and April, and that under the summer season in 

 July to September. The rainfall of May and June is negligible and 

 seldom has any influence on feed production. 



The rainfall record is taken in the 204-acre pasture shown on the 



map (fig. 1). 



In a general way Table I shows that the yield is dependent 

 upon the quantity of rainfall. Quantity, however, is not the only 

 factor, as will be readily seen. Its distribution is of extreme 

 importance. This feature is not shown in the table. It can be 

 shown only by a detailed account of the precipitation, which it is 

 not considered necessary to publish at this tune. The most im- 

 portant point of all brought out by the table is the comparative 

 uniformity of production during the last years and the increase over 

 earlier years. Both of these facts tend to show that the production 

 of the field has been decidedly on the increase and that it may now 

 be at its maximum, which was reached in about three years after its 

 inclosure. Whether the production from now on will be dependent 

 upon rainfall alone remains to be seen, but so far as these records go 

 that is to be expected. It is also to be expected that from now on 

 there will be little, if any, increase in production due entirely to 

 protection. On the other hand, yield alone is only one phase of the 

 improvement which may take place, As pointed out elsewhere, this 

 improvement may be as much a matter of the supplanting of annuals 

 by perennials of greater value as it is of actual number of pounds of 

 feed produced. This improvement, it is believed by the writer, will 

 take place to some extent under future protection, but it is believed 

 that the maximum tonnage has been reached and that future fluc- 

 tuations will be due in largest measure to variation in rainfall. 



The general correlation between the rainfall and the yield of forage 

 is of course very striking, as rainfall is always the most important 

 factor of production here. But the production of 520 pounds of 

 forage on 3.29 inches of rainfall in the spring of 1903 is out of all 



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