ASPEN IN THE CENTRAL ROCKY MOUNTAIN REGION 
25 
brush (Pachystima rmyrs'mites) ; Oregon grape (Odostemon repens), 
particularly at lower altitudes; and buffalo berry (Lepargyrea cana- 
densis). Sagebrush (Artemisia spp.) and oak (Quercus gambelii) 
are unable to grow under aspen shade, but frequently fringe aspen 
stands. Maples (Acer glabrum and A. g randidentatum) are found 
occasionally, particularly in wet places, and chokecherry (Prunus 
melanocarpa) is common in the aspen zone both in the direct shade 
of aspen and in the open. Much the same is true of serviceberry 
(Amelanchier alnifolia), but which goes to much lower elevations 
than aspen. Mountain ash (Sorbus sambuci folia) is common in 
many places at higher elevations in the spruce-fir type. Owing to 
the wide extent of the aspen type, a vast number of herbaceous 
species are characteristic associates of aspen in the different re- 
gions, but none can be selected which is characteristic of aspen areas 
in general. As a class they are moisture-loving perennials and an- 
nuals, both herbs and grasses. 
GROWTH 
In all discussion of growth and development of aspen, the factor 
of site must constantly be kept in mind on account of the sensitive- 
ness of aspen to site factors. Height growth is most seriously af- 
fected; indeed, this has been made the measure of site differences. 
Diameter growth is slower on poor sites also, although it is not re- 
duced as fast as height growth; and accordingly on poor sites the 
height is less for a given diameter than on good sites where the trees 
are remarkably tall and slender. The average development of trees 
on a limited area of site quality 1 in central Utah, shown in Table 12, 
indicates the best that can be expected of aspen in the central Rocky 
Mountain region. 
Table 12. — Groicth of aspen, Clear Creek, Utah 
Age 
10 years 
20 years 
30 years 
40 years 
50 years 
60 years 
70 years 
80 years 
Diameter 
breast 
Height 2 
height l 
Inches 
Feet 
1.8 
12.5 
3.0 
21.0 
4.2 
30.0 
5.0 
38.0 
6.0 
45.5 
7.0 
52.5 
7.9 
57.5 
8.8 
64.0 
Age 
90 years 
100 years. 
110 years 
120 years 
130 years 
140 years 
150 years 
Height 
Feet 
66.0 
68.5 
71.5 
73.5 
74.5 
75.0 
75.5 
i Basis, 261 trees. 2 Basis, 124 trees. 
HEIGHT GROWTH 
Height growth is extremely rapid during the first few years, pro- 
vided the sprouts have full light. The rapidity of this growth is 
especially marked when compared with the slowness of conifers 
associated with aspen. The average height growth of aspen sprouts 
from four clear-cut areas is fairly representative of sprout growth on 
sites 1, 2, and 3, early growth being much less dependent on site 
than is more mature development (Table 13). 
