EFFECT' OF GRAZING UPON ASPEN REPRODUCTION. 



RELATION BETWEEN INTENSITY OP GRAZING AND INJURY TO SPROUTS. 



The character of injury to sprouts will, of course, largely determine 

 (1) the subsequent density of the aspen stand, (2) the ultimate form 

 of the trees, (3) the subsequent rate of growth, and (4), to a con- 

 siderable extent at least, the size of the trees and the commercial 

 value of the timber. The removal of the leader or terminal shoots 

 of aspen reproduction, for instance, may* destroy the symmetry of 

 the tree, especially if the leader is removed more than once. The 

 injury caused by the destruction of lateral branches is chiefly physio- 

 logical, the nutriment on which the specimen may build being 

 roughly proportionate to the number of laterals; i. e., to the leaf 

 area. 



The extent of browsing of leaders and laterals, or both, the mor- 

 tality due to excessive browsing, and the number of sprouts unin- 

 jured on the plots in standing timber during 1915 and 1916 are sum- 

 marized in Table 3. The greatest number of specimens were under 

 observation during these two years. 



Table 3. 



-Character and extent of injury to sprouts according to intensity of grazing, 

 seasons 1915 and 1916. Plots in standing timber. 



Season and grazing intensity. 



Total 

 sprouts 

 killed. 



Ungrazed 

 sprouts. 



Leaders 

 browsed. 



Leaders 



and 

 laterals 

 browsed. 



1915: 



Lightly grazed 



Moderately grazed 

 Heavily grazed 



1916: 



Lightly grazed 



Moderately grazed 

 Heavily grazed 



Per cent. 

 15.9 

 17.5 

 26.1 



13.5 

 12.9 

 63.2 



Per cent. 

 39.1 

 30.6 

 14.0 



65.9 

 54.2 

 12.9 



Per cent. 



4.5 



4.3 



21.5 



7.8 

 14.6 

 4.4 



Per cent. 



2.3 



7.7 



15.1 



7.1 

 12.8 

 16.7 



Both in 1915 and 1916 the mortality was practically the same on 

 lightly grazed and on moderately grazed plots, the average percentage 

 being 14.9 (fig. 1 ) . On the heavily grazed plots, however, the mortality 

 of sprouts was appreciably greater, being 26.1 per cent of the total in 

 1915 and 63.2 per cent in 1916. The percentage of ungrazed sprouts 

 in 1916 was more than five times as much on the lightly grazed areas 

 and four times as much on the moderately grazed areas as on the 

 heavily grazed plots. The general tendency is the same in the 1916 

 figures. The averages for 1915 and 1916 on lightly grazed plots was 

 52.5 per cent, on the moderately grazed areas 42.4 per cent, and on 

 the heavily grazed plots only 13.4 per cent. 



The number of terminal shoots or "leaders" removed was prac- 

 tically the same (averaging 4.4 per cent) on lightly and on moderately 

 grazed plots in 1915; but on the heavily grazed areas it was consid- 

 erably larger, amounting to 21.5 per cent. In 1916 the terminal 

 shoots of 7.8 per cent of the specimens were consumed on lightly 



