|Aspen - Forest Management
Sustaining Aspen in Western Landscapes
Aspen is a relatively minor component of Rocky Mountain landscapes,
typically comprising less than 5% of the forest area (but covering
more than 50% in some landscapes). Although aspen forests are is
a relatively minor component of Rocky Mountain landscapes, they
are important for many aspects. Aspen forests have twice the diversity
of understory plants, including rare and endemic species, than conifer
forests. A wide range of wildlife, from cavity-nesting birds to
elk, use or depend upon aspen stands. Aspen plays an important role
in the fire regimes of the Rockies; aspen stands provide natural
fire breaks that may limit the extent of wildfires. Perhaps the
most visible role played by aspen is its scenic beauty.
The already-limited extent of aspen in Rocky Mountain forests may
be declining. Much of this “decline” results from normal
succession processes toward conifer dominance. High populations
of elk may also preventing natural regeneration of aspen clones
in some cases. The actual picture of aspen forests across the Rockies
is highly variable, and the presence of conifers and elk in aspen
stands may or may not indicate a progressive loss of aspen.
The story of aspen in Rocky Mountain landscapes is clearly a diverse
story; some areas are losing aspen as a result of normal succession
to conifers, and other areas are showing a lack of aspen regeneration
as a result of stand aging, fire suppression and excessive browsing.
Aspen forests are stable or increasing in some areas. Our choices
about land management activities in the coming decades will determine
the extent of aspen forests for the next century.
The international symposium "Sustaining Aspen in Western Landscapes"
held June 13-15,200 in Grand Junction, CO, gave over 250 researchers,
managers, and people with strong interests in aspen and western
landscapes the opportunity to share scientific knowledge about aspen.
The proceedings of that meeting “Sustaining aspen in western
landscapes” published in 2001 by RMRS (Proceedings RMRS-P-18)
summarize the state of knowledge about aspen ecology, the condition
and trends in aspen ecosystems in western North America and Canada,
and present human dimension and management options for sustaining
aspen. Thirty-seven peer-reviewed papers, four presentation abstracts,
and sixteen poster abstracts cover topics including landscape dynamics
of aspen and conifer forests, animal/aspen interactions, the ecological
role of aspen, physiology and production ecology, aspen forest products,
and human dimensions.
Citation: Shepperd, W. D., Binkley, D. Bartos, D. L., Stohlgren,
T. J., Eskew, L. G. comps. 2001. Sustaining aspen in western landscapes:
Symposium proceedings. Proc. RMRS-P-18. 2000, June 13-15; Grand
Junction, Co. Fort Collins, CO: US Department of Agriculture, Forest
Service, Rocky Mountain Research Station: 460 p.
stand classification study
– A data based classification system was developed using clustering
and multivariate analysis techniques to define seven categories
of aspen stands in the Central Rocky Mountains. Each
of the stand categories possess unique life history, stocking,
and growth characteristics important to the various management
objectives for aspen in this region. An article
describing the classification system was published in the
Western Journal of Applied Forestry.
A computerized classification
program (ASPENCLS) was developed and tested as a possible
means of identifying potential old-growth aspen stands.
Although complete, this study continues to be a source of
much of the aspen information requested by users in technology
transfer activities. (photo is 64 KB)
Example of "Dixie
- a prescribed burn used to regenerate aspen:
credit: Brian Ferguson, Dixie National Forest (photo is54
study attempted to regenerate an aspen clone in extreme decline
on the Kaibab NF northwest of Flagstaff. Aspen can truly
be termed "threatened and endangered" in this landscape.
Only two live stems remained in this clone which is
the only aspen for several miles in any direction in an otherwise
pure ponderosa pine forest. However, browsed suckers
were observed at 30 root nodes in a 1/4 acre area surrounding
the two remaining stems.
We tested the hypothesis that removing competition, and browsing
pressure would allow this clone to naturally regenerate without
cutting existing aspen stems or roots. Our treatment
strategy was to remove all conifers within the 1/4 acre suckering
area and to fence it with a 7 ft. hog-wire fence.
This treatment was accomplished by Tim McGann and Kaibab personnel
in November, 1991. By fall 1994, the fenced area contained
274 new suckers, some over 8ft tall. Both parent stems
are still alive too. We have discovered that swallowtail
butterfly larva feed extensively on the leaves of the suckers
in this clone, illustrating yet another role of aspen in southwestern
ecosystems. Although this is an extremely small-scale study,
it has demonstrated a means of saving critical aspen clones
from extinction. (photos are 169 KB total)
study was installed in a declining aspen stand also located
north of Flagstaff on the Peaks District. This stand
was partial-cut several years ago in an attempt to regenerate
the clone, but was not fenced and the regeneration succumbed
to animal browsing. Only large, widely-spaced residual
stems and numerous stumps remained.
We felt that sufficient light existed for suckers to grow,
so elected to apply a root stimulation treatment to sever
lateral roots and promote suckering without cutting any overstory
trees. Half of this stand was treated in the spring
of 1992 by the District's crawler tractor equipped with a
ripper. The tractor ripped around each surviving overstory
tree, staying at least 20 ft. away from the stem in an attempt
to avoid over-stressing the parent trees. Treated and
untreated control areas were fenced prior to the 1992 growing
season and a grid of 1/100ac regeneration plots was established.
To date, the treatment has produced an average of 2000 suckers/ac
while the fenced-control area has an average of 800 new suckers.
All overstory trees still survive and appear to be increasing
in vigor. (photo is 78 KB)
removal study.--Experience has
shown that regenerating aspen in this ecosystem requires fencing
to protect suckers from browsing elk. However, it was
not known how long the fence needed to remain in place.
In October, 1991 we removed the fence surrounding a 16 acre
aspen sucker stand north of Flagstaff, Arizona to test whether
the trees were large enough to be out of reach of the animals.
The site had been fenced for five years following clearfelling
of several clones that comprised the original stand. The regenerated
stand averaged 20,000 stems/ac with dominant stems over 10 ft
By October, 1992, most stems in one clone had been severely
damaged by elk. Animals broke many stems to reach the terminal
foliage, often infecting the residual stem with Cytospora canker.
This clone was almost completely gone by fall, 1994. Although
other clones also suffered extensive browsing, stems larger
than 1.5 in dbh seem to be too large for animals to break. It
appears that fencing must
remain in place until most stems are this size to successfully
regenerate aspen in this ecosystem. (photos are 153 KB total)