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Linda Joyce
Rocky Mountain Research Station
240 West Prospect
Fort Collins, CO 80526
Phone: 970-498-2560
ljoyce@fs.fed.us
 United States Department of Agriculture Forest Service.USDA logo which links to the department's national site.Forest Service logo which links to the agency's national site.
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.

 

Aspen 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 Heat" - a prescribed burn used to regenerate aspen:

Photo credit: Brian Ferguson, Dixie National Forest (photo is54 KB)

 

Clonal rehabilitation demonstration.--This 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)

 

Root stimulation study.--This 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)

 

 

Fence 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 in height.

 

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)

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