18 BULLETIN 741, U. S. DEPARTMENT OF AGRICULTURE. 



HEIGHT AT WHICH REPRODUCTION IS EXEMPT FROM GRAZING 



INJURIES. 



The factor which chiefly determines the time of exemption of the 

 reproduction from destructive browsing is the height of the sprouts. 

 Observations have shown clearly that as soon as the terminal shoots 

 and some of the lateral branches have attained a growth beyond 

 which stock generally browse, the reproduction is no longer in danger 

 of serious damage. Since sheep are particularly destructive to 

 young aspen reproduction, detailed observations as to, the height 

 at which they browse were recorded both on the open range and on 

 controlled plots. The height to which cattle browse was observed 

 under range conditions only. 



HEIGHT TO WHICH SHEEP BROWSE. 



The height to which sheep browse depends, of course, upon the 

 palatability of the plants that grow within the reach of the animals, 

 as well as upon the particular breed of sheep. Sheep relish woody 

 plants, and they browse the aspen reproduction at as great a height 

 as other highly palatable species. The sheep under observation 

 consisted of about equal numbers of ewes and lambs of the Eam- 

 bouillet and merino breeds, chiefly the former. The animals of 

 both breeds were of about average size. 



In observing the height of grazing on the range it was necessary to 

 adhere almost entirely to reproduction in standing timber, as rela- 

 tively little aspen timber on the sheep allotments has as yet been 

 clear-cut or heavily thinned. For this reason the height of the 

 sprouts, the stand of which was usually quite sparse and scattered, 

 was uneven and often considerably below the maximum height at 

 which sheep may browse. Accordingly, to determine the height of 

 aspen browsed with unquestionable accuracy, and to secure a basis 

 for future management of grazing in the aspen type, the observations 

 on the range were supplemented by a carefully planned experiment 

 on a clear-cut fenced inclosure where the sprouts varied in height 

 from 20 to 70 inches, the majority having a height of about 45 inches. 



The plot was one-fourth of an acre in area. Two 5-year old ewes 

 and three lambs 3 months old were grazed on the plot as long as 

 the feed, consisting of a luxuriant undergrowth of grasses, pea vines* 

 a variety of weeds, and some shrubby growth, was sufficient to 

 sustain the animals at their original weight. Accordingly, the plot 

 was grazed much more closely than would be possible over the range 

 generally where the lands are handled on the basis of a sustained 

 annual yield. The plot in question was clear-cut late in the autumn 

 of 1913 and the sheep were placed on it in August, 1916, so that the 

 major portion of the reproduction was about 3 years of age. At 

 the time the sheep were turned on there was a stand of 30,056 sprouts 



