24 BULLETIN 1291, U, S. DEPARTMENT OF AGRICULTURE 
joining a white fir stand shows a total of 4,246 conifer seedlings per 
acre which have come in within the 50-year period following the last 
fire. All age classes are represented, showing a sustained invasion of 
conifers. Their apportionment is as follows: 
The 1-10 year class shows 1,716 trees per acre; the 11-20 year 
class, 1,360 ; the 21-30 year class, 796 ; the 31-40 year class, 176 ; and 
the 41-50 year class, 198 trees per acre. 
This shows an establishment of about 200 trees per decade which 
will go into the final stand, a rate of regeneration which is satis- 
factory for a white fir-Douglas fir site. In the Engelmann spruce- 
alpine fir type, reproduction proceeds at a much more rapid rate 
than this, but this is more necessary, as this type is much more dense 
and a larger number of stems per acre will be carried through the 
entire rotation. On the whole, it can not be said that the extremely 
rapid regeneration of aspen gives it any particular advantage ovei 
conifers in forest management. 
THE STAND 
Aspen exists typically in even-aged stands (unusually over 40 
years of age) in the Utah region, indicating their origin from 
burns. Two-storied stands are also common, an even-aged overwood 
with either an even-aged underwood, found where light fires have 
run through aspen, or with an uneven-aged underwood, found when 
the overwood begins to break up naturally. With the elimination of 
fire this last form of stand is becoming increasingly prevalent. 
(PL VII, fig. 1.) All-aged stands are also found. Even when an 
even-aged stand goes to pieces naturally, tree by tree, the new growth 
tends toward the even-aged, for the period of decadence of the parent 
stand is usually of relatively few years and the reproduction will 
contain only an approximately equal number of age classes. This 
partially uneven-aged stand will mature much more unevenly than 
its parent did, however, and its successor will be still more uneven- 
aged until at last a fully all-aged stand is formed. 
ASSOCIATED SPECIES 
Aspen stands often give the appearance of permanence (climax 
type) on account of their purity over large areas, but there is little 
evidence that this is due to anything but fires in the past and slow 
seeding in of conifers at the present time. Nevertheless, as a man- 
agement type a great many areas must be considered permanent for 
a very long period of years. Douglas fir, white fir, and lodgepole 
pine are typical associates of aspen throughout the Rocky Mountain 
region. Alpine fir, Englemann spruce, and the conifers which 
seldom form stands, such as limber pine and bristle-cone pine (Pinus 
arixtata), are less frequent associates. All parts of the type can 
logically be occupied by some of these species to the exclusion of 
aspen as a type, although total exclusion of all aspen trees is hardly 
possible in the open coniferous stands of this dry region (PI. VII, 
fig- 2). 
Among the more common brushy associates are snowbrush (Si/m- 
phoricarpos oreophilius) , very common in the Utah region; myrtle 
