IMPORTANT WESTERN BROWSE PLANTS Ri 
local browse on western ranges, the aspen is most important though 
others are nearly or quite as palatable. 3 
Aspen (Populus tremuloides),® often called quaking aspen (pl. 
1, B), occurs from Labrador and Newfoundland to New Jersey, 
Pennsylvania, and, in the Appalachian Mountains, to eastern Tenn- 
essee, its westerly range extending to Kansas, New Mexico, and 
California and thence to Alaska; and east to Quebec; southward it 
ranges in the mountains into Lower California, Sonora, and Chi- 
huahua, Mexico. Aspen grows in a great variety of soils and will 
endure a considerable degree of aridity; its best development is 
obtained in deep, moist, rich, but well-drained soils. Few trees will 
so successfully endure continued low temperatures, as its extended 
range beyond the Arctic Circle attests, and few tree species are 
more intolerant of shade. In the North it occurs from sea level up 
to 2,500 or occasionally as high as 3,500 feet. In the Rocky Mountains 
and Great Basin it ranges between about 6,000 and 10,500 feet. 
At the extreme southern limit of its range it is never found below 
8,000 feet. Vegetative reproduction in this species is abundant 
and aggressive. 5 
Because of its typically open stand and penchant for moist, deep, 
and fertile soils, the aspen type is often an indicator of naturally 
superior vegetative conditions and frequently supports an under- 
story of weeds and browse that is esteemed highly by livestock. 
Moreover, the aspen itself when not too large and beyond their 
reach is very palatable to sheep and cattle, which browse exten- 
sively on the foliage and twigs, especially in the fall. E. R. Hall 
reports that aspen is the favorite food of the mule deer on the 
Kaibab National Forest. 
The best utilization of the scrubbier aspen stands is normally 
for grazing, but where the species is desirable for its wood it is 
often necessary to adopt protective measures, especially with sheep. 
Aspen, when not valued locally more for its wood, is probably of 
especial value on sheep range, at least during the forepart of the 
season and at the higher elevations where the growth is scrubby. 
In the Northwest, however, it is regarded as somewhat more pala- 
table to cattle than to sheep in the summer (July-August) and 
equally palatable in the fall (September-October). Sampson (///) 
has shown that cattle will browse aspen up to 60 or sometimes 
to 70 inches, and that the injury they cause aspen reproduction is 
usually but shght unless the lands are overgrazed or the animals 
inclined to congregate for extended periods where the aspen repro- 
duction occurs. He notes that sheep are far more prone than cattle 
to eat the woody stems of aspen, but that sprouts averaging 45 
inches high are practically exempt from destruction by sheep, so 
| that three years of protection (estimating the average growth of 
sprouts to be 15 inches a year) is sufficient to place aspen sprouts 
beyond serious injury by sheep and four or five years of protection 
beyond injury by cattle. 
6 Some authors regard the aspen of the Western States as a distinct species under the 
name Populus aurea Tidestrom, or as a variety (P. tremuloides aurea (Tidestr.) Daniels). 
In the Forest Service the same term applies to both types. 
27259°—31 2 
