EFFECT OF GRAZING UPON" ASPEN REPRODJTCTIOISr. 9 



considerably larger than the percentage of the remaining uninjured 

 sprouts. In addition to the mortality and injury due to browsing, 

 11.7 per cent of the sprouts were killed and 6.3 per cent injured in 

 varying degrees of seriousness by causes other than browsing. 



(2) The extent of injury to and mortality of sprouts in standing 

 timber was in direct proportion to the intensity of grazing; also the 

 character of injury, such as the removal of the leader, for example, 

 was notably greater on heavily grazed plots than on moderately and 

 lightly grazed areas. In 1915, for example, an ayerage of 4.4 per 

 cent of the leaders were removed on lightly and moderately grazed 

 plots, while on the heavily grazed areas 21.5 per cent of the leaders 

 were removed. 



(3) Considerable variation in the extent of injury and mortality 

 to the reproduction occurred in different seasons, the variation in 

 injured sprouts being over 25 per cent and in killed sprouts over 10 

 per cent during the five years of study. Within a single season, 

 however, no appreciable variation in degree and number of injured 

 sprouts was observed so long as the leafage remained intact. 



EFFECT OF CATTLE BROWSING. 



Plots in standing aspen timber grazed exclusively by cattle were 

 selected early in the spring of 1915. In addition to the detailed data 

 on character and extent of injury to aspen reproduction by cattle in 

 1915 and 1916, data on the extent of injury by browsing prior to the 

 establishment of the sample plots were afforded by the older speci- 

 mens under observation. Accordingly, injuries covering a great 

 many years were recorded. 



The general grazing injuries to the reproduction are summarized 

 in Table 6. The data are grouped according to intensity of grazing, 

 both as to total injury regardless of the height classes of the sprouts 

 and as to injury to the different height classes. Table 6 shows that 

 the extent of injury in 1915 and 1916 varies directly with the close- 

 ness to which the range was grazed, being least, indeed practically 

 nominal, on lightly and moderately cropped plots and relatively 

 heavy (17.5 per cent in 1915 and 36.1 per cent in 1916) on heavily 

 grazed areas. While the number of browsed sprouts was fairly 

 large on the closely grazed plots, the injuries were in no instance 

 especially serious, nor was the extent of damage anywhere near as 

 great as that caused by sheep. The damage done by cattle to repro- 

 duction of a given height was in no case severe. The average per 

 cent of injury to sprouts above 1J feet in height was approximately 

 the same as that of sprouts of the 6-inch to 1^-foot class. Thrifty 

 aspen reproduction of varying age and size is found throughout the 

 aspen type in localities where cattle only have been permitted to 

 graze moderately for a number of years. This would indicate that 

 76783°— 19— Bull. 741 2 



