26 BULLETIN 141, U. S. DEPARTMENT OF AGRICULTURE. 



large proportion of the nonbrowsed sprouts are killed by causes other 

 than grazing. In standing timber on cattle range also the injury- 

 varied according to grazing intensity, but was less than on the sheep 

 range. During 1915 and 1916 the average percentage of injured and 

 killed sprouts by cattle browsing was 1.6, 2.4, and 26.8 on lightly, 

 moderately, and heavily grazed plots, respectively. 



(5) On clear-cut lands, where the reproduction is conspicuous and 

 the stand even, the annual mortality due to sheep grazing is exceed- 

 ingly heavy. As a rule three years of successive sheep grazing on 

 such lands results in the destruction of the entire stand. Some injury 

 is also caused by cattle on clear-cut areas, but unless the range is 

 stocked with cattle beyond its normal carrying capacity there is little 

 danger of the reproduction being destroyed beyond the requirements 

 necessary for the establishment of a full commercial stand. 



(6) Only slight difference is recorded in extent and character of 

 browsing either by sheep or by cattle on different height classes of 

 reproduction, so long as the total height growth of the sprouts has 

 not passed the limit at which stock find the food accessible. 



(7) A comparison of the character and intensity of browsing shows 

 that a notably greater proportion of the woody stems is consumed 

 by sheep than by cattle. Even in the autumn after the leaves have 

 dropped sheep devour a considerable quantity of the stems of a single 

 season's growth regardless of the presence of an abundance of choice 

 forage. In the case of cattle, however, the naked stems are practi- 

 cally untouched. 



(8) Aspen sprouts are not necessarily permanently injured, nor 

 will the mature tree be lacking in form or symmetry as a result of the 

 removal once or twice of the terminal shoot. Nearly any one of the 

 lateral branches which grow near the terminal shoot appears to be a 

 potential terminal and may readily assume the function of the ter- 

 minal itself. The destroyed leader is very commonly and promptly 

 replaced by shoots originating from adventitious buds near the ter- 

 minal. On the other hand, the removal of both the lateral branches 

 and the terminal shoot to such an extent as to interfere appreciably 

 with photosynthesis and the nutrition of the specimen readily weak- 

 ens and decreases its subsequent rate of growth materially. If the 

 normal leaf surface is not readily replaced and then maintained, death 

 is the inevitable result. 



(9) On lands protected from grazing aspen sprouts are produced 

 only during the first two seasons after cutting. On grazed lands a 

 considerable number of sprouts are sent up for three successive sea- 

 sons following the removal of the timber. The third year's repro- 

 duction, however, appears from two to five weeks later than that 

 produced in the two previous seasons and is, for the most part, 



