EFFECT OF GRAZING UPON ASPEN REPRODUCTION. 21 



The height of browsing increases gradually with the increase in 

 the height classes of the reproduction up to the fifth class; i. e., from 

 21 to 41.1 inches. From this point on up to the ninth class the height 

 of the browsing varies slightly above or below the 40-inch mark. 

 In the ninth class occurs the maximum average height of 41.8 inches. 

 The average height at which the 69 grazed sprouts in the transect 

 were grazed was 38.1. This is about the height of the top of the 

 heads of mature Rambouillet and merino sheep. 



Sprouts the terminal shoots of which have attained a height of 

 40 inches or so are apt to suffer only slight permanent injury, and 

 extensive observations on the range and on the various check plots 

 have shown that reproduction having an average height of 45 inches 

 is practically exempt from serious injury. Hence lands supporting 

 reproduction averaging 45 inches in height may be grazed with 

 practically no injury to the terminal shoots. Moderate browsing of 

 some of the lateral branches will occur, of course, as long as they are 

 easily within the reach of sheep, but the effect of such browsing is 

 insignificant so far as concerns the development and health of the 

 specimen. 



HEIGHT TO WHICH CATTLE BROWSE. 



It has been pointed out that reproduction only a few inches or so 

 in height is subject to about the same degree of browsing by cattle 

 as is reproduction of greater heights. Thus, contrary to what might 

 be expected, sprouts two or three feet high which by virtue of their 

 greater conspicuousness might be presumed to afford more con- 

 venient browsing than the shorter specimens are nevertheless dam- 

 aged as little as any of their younger associates. 



Considerable variation is observed in the height of the browsing 

 by cattle. Isolated instances have been recorded of the removal of 

 leafage to a height of about 70 inches, but browsing at such a height 

 is exceptional and o.f little economic significance. Damage of greater 

 severity occurs between heights of 55 and 60 inches, the latter figure, 

 however, being about the minimum at which twigs and stems are 

 eaten. Thus in localities where cattle are apt to drift and linger 

 and where it is desired to reforest the lands fully the reproduction 

 should be permitted to attain a growth of not less than 5 feet prior 

 to heavy stocking. Obviously, then, lands which are to be reforested 

 should not be used as salting grounds until a sufficient portion of the 

 reproduction has attained a height beyond which destructive brows- 

 ing is likely to occur. 



RATE OF GROWTH OF ASPEN REPRODUCTION. 



In the management of grazing on cut-over lands it is necessary to 

 know, in order to make the most judicious use of the knowledge of 

 the height which aspen reproduction must attain to be exempt from 



