GRAZING AND FORAGE PRODUCTION ON NATIONAL FORESTS 19 



The difference in the time at which the forage is sufficiently 

 advanced to allow cropping on north and on south exposures at 

 the same elevation in the oak-brush type may in extreme cases 

 amount to two weeks. The difference is much less pronounced 

 at the higher elevations than in the lower belts, except on very steep 

 slopes where large snowdrifts occur. 



On the more gently sloping north and south exposures at the same 

 elevation the forage is sometimes in practically the same stage of 

 development when the range as a whole is ready for cropping. 



In order to study plant development on different slopes and ex- 

 posures, a phenological table giving in a number the stage of develop- 

 ment of the plant as a whole was developed, as follows : 



Beginning of growth (buds of foliage or blossoms swelling) 5 



Vegetative development (leaf or leaf blade in evidence) 10 



Leaf sheaths swelling (inflorescence in the "boot") 30 



Inflorescence showing but flowers not expanded 40 



Inflorescence showing most of flowers fully expanded 60 



Seed fully developed, partly or entirely disseminated 100 



In accordance with these values representative species were 

 observed on different slopes and exposures of the same elevation in 

 all major forage types. The numerical values assigned to height 

 or extent of leaf expansion were recorded only after actual measure- 

 ments had been made ; the extent of the swelling of the buds and the 

 development of the flowers and fruit were determined ocularly. 

 The method must be used with discretion as to individual species, 

 but when a considerable number of species are observed, the results 

 should give an approximate ultimate average. In general, when 

 these numbers are used the average which indicates vegetative 

 readiness will be from 20 to 30 per cent, according to the composi- 

 tion of the vegetation. 



The results of some observations in the oak-brush and in the 

 spruce-fir types are given in Table 4, and their averages in Figure 8. 



The results show that there is considerable variation in the time 

 interval of plant development on north and south exposures. The 

 forage in the oak-brush type develops much earlier on south than 

 on north exposures; but with increase in elevation this difference 

 in development decreases until at elevations of 10,000 feet in the 

 spruce-fir type the date of vegetational readiness for grazing is 

 practically the same for the two exposures. 



It was also found that for each 1,000 feet increase in elevation 

 the date of vegetational readiness is retarded approximately 18 days 

 on south exposures and about 11 days on north exposures, or about 

 14 days on an average. This average delay varies, however, from 

 10 to 20 or more days in the intermountain region, according to 

 local climatic conditions and the type and vigor of vegetation. 



CLOSING OF THE SEASONAL GRAZING PERIODS 



The time when livestock should be removed from the spring range 

 to the summer range is determined chiefly by (1) the stage of growth 

 and the abundance of forage on the summer range, (2) the graz- 

 ing capacity of the early range as compared with that of the sum- 

 mer range, (3) the palatability of the forage on the spring range 

 and the thriftiness of the animals grazed, (4) the water supply on 

 both ranges, and (5) the need for and value of the forage on the 



