8 BULLETIN 1405, U. S. DEPARTMENT OE AGRICULTURE 



remain until the growing season is well advanced. In the spruce- 

 fir zone they often remain until the latter part of August, and 

 in some years a few last almost throughout September. Their 

 presence no doubt has some cooling effect on the air tempera- 

 tures in these zones. 



Scarcity of moisture and high temperatures in the oak-brush zone 

 are responsible for the presence there of drought-enduring vegeta- 

 tion which is less succulent and somewhat less palatable than that 

 at the greater elevation. 



Insufficient moisture during the main growing season will in all 

 zones result in a comparatively small yield of herbaceous forage. 

 On the other hand, warmer air temperatures may cause greater 

 volume production if sufficient moisture is present, especially in the 

 spruce-fir and aspen-fir zones. 



GRAZING PERIODS 



The proper time for grazing to begin on a range, or the time of 

 " range readiness," may be defined as the date in any one year 

 when the range first reaches the condition in which there is suffi- 

 cient feed to keep livestock in thrifty condition and when the stock 

 may be admitted without serious impairment of the growth and 

 reproductive processes of the more important forage plants. To 

 determine when this condition is reached is a problem of prime im- 

 portance in economical range management. 



RELATION OF HEIGHT OF HERBAGE TO RANGE READINESS 



EFFECT OF TIME OF FIRST CROPPING ON EARLY HEIGHT AND FORAGE YIELD 



An experiment was conducted on typical range plants to deter- 

 mine (1) the effect on early yield and vigor of growth of cropping 

 at different stages of development, and (2) whether a certain aver- 

 age height growth of herbaceous vegetation is a reliable basis upon 

 which to judge range readiness. Five different species of range for- 

 age plants were used, namely, Letterman needle grass (Stipa letter- 

 Qnarii), violet wheat grass (Agropyron violaceum), mountain brome 

 (Bromus polyanthus), wild geranium {Geranium viscosissimum) , 

 and mountain dandelion (Agoseris pumila). In each species 10 

 specimens for clipping and 10 for checks in each of three series 

 were selected more or less at random on the range in the aspen-fir 

 type at an elevation of 8,700 feet. Care was exercised in all cases 

 to locate plants of nearly the same height and in as vigorous a 

 condition as possible. Accordingly, comparatively young plants 

 were chosen — the bunch grasses, for instance, having a crown diam- 

 eter usually not in excess of about 2.5 inches. Each specimen was 

 staked and numbered. The herbage of those clipped was removed 

 by a method somewhat resembling grazing, the leafage being cut 

 about 1 inch above the ground's surface. 'The material removed 

 from each plant was preserved separately and the dry weight was 

 recorded. The first series of specimens were first measured and 

 harvested on June 1, when the grass blades and the leafage of most 

 other herbaceous plants were only 2 inches high or less. The second 

 series were first harvested on June 10 and the third series on June 



