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The Science of the Pando Tree

Fences to Save Aspen: Good, Bad, Ugly

Paul C. Rogers | Director | Western Aspen Alliance

April 2021

In valued aspen locations around the West, we frequently see small portions of forests fenced, but there is often little or no explanation for this intrusion. After all, we visit these treasured landscapes to engage with nature unfettered, not to encounter visual and physical impediments. To understand why these barriers are commonly located within aspen communities it is useful to gain a bit of background before addressing broader ecological and philosophical perspectives on this phenomenon.

Quaking aspen are widely revered by range and wildlife managers alike for their diverse and nourishing array of understory plants. Young aspen suckers (asexual sprouts directly from parent roots) are particularly favored by deer, elk, cattle, and sheep for their highly nutritious leaves and twigs. During the late summer and early autumn aspen may be the only green, nutritious, component of forests available as forage. Fortunately, aspen leaves contain defense compounds (phenolic glycosides and condensed tannins) that may deter herbivores, at least partly, from devouring young suckers. However, with high animal concentrations—often a mix of wild and domestic herbivores on the same landscape—defense mechanisms may not sufficiently deter browsing on regenerating aspen suckers. A hungry animal will eat leaves that don’t taste good rather than eat nothing at all. If these consumption patterns persist over many years aspen forests begin to lose their age and structural complexity. Eventually, entire aspen groves may collapse as aging trees die and there is no progeny to replace them. This situation seems particularly serious in stable (nearly pure) aspen forests, like Pando, where uncommon large disturbances offelittle hope of broad forest rejuvenation (see Fire in Aspen Forests).

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On the Fishlake National Forest’s Pando aspen clone (near Fish Lake proper), fences were erected in 1992, 2013, and 2014 (the 2014 fence upgraded and greatly expanded the 1992 fence) to protect young aspen suckers.  Ongoing monitoring activities are attempting to document where livestock and wildlife browsing are threatening future aspen trees.  In some cases, there is clear evidence of aspen collapse related to intensive browsing. The presence of large carnivores, such as wolves, grizzly bears, and cougars, may deter aspen browsing by keeping livestock and wildlife on the move.  Domestic livestock may be more easily herded to prevent over browsing aspen.  Range and wildlife managers are now working collaboratively to curtail aspen recruitment failure while continuing to sustainably utilize forage resources.  Cooperative research and monitoring, as well as prudent use of fire, tree harvest, and post-treatment protection, will be required to overcome the widespread lack of aspen recruitment.

While fences may provide clear illustration of browsing problems—robust new growth takes place within the exclosure, but no young stems are visible outside fences—they don’t necessarily help us address the issue at larger scales.  In other words, we’re avoiding the base cause of the problem, over-browsing by domestic and wild ungulates, while providing an aspen zoo of sorts within caged enclaves.  Some have termed this a “band-aid” approach to land management; where we focus on curing the symptoms without combating the actual cause.  Secondarily, it is worth considering a broader ethical point: do we wish to see barriers throughout our forest reserves as a result of managers who control browsing livestock, deer, or elk being unable to make adjustments, albeit difficult ones, in how they do business?  A reasonable compromise approach would be to perform needed triage on valued aspen communities, while we begin the harder tasks of finding reasonable solutions among interest groups supporting wildlife and livestock.  Of course, a key to this whole approach, sometimes called “adaptive management,” is to continually check on our progress via monitoring the condition (a.k.a., taking the pulse of the patient) as we go.  If negative or positive trends develop in basic forest indicators, like number of browsed stems or viable saplings, appropriate adjustments to the course of action are taken to forestall system collapse.  

As we manage any valued landscapes, it is advantageous to have such short-term and long-term strategies working simultaneously.  In this manner, we use prudent strategies of best-available-science, alongside societal needs and management resources, to make sound decisions on behalf of nature.  Fenced forests provide clear demonstrations of browsing problems, but we don’t want them as a forest aesthetic in perpetuity.

About the Author

Paul Rogers Director Western aspen alliance

Paul C. Rogers is a biogeographer, forest ecologist, and Director of the Western Aspen Alliance at Utah State University. Dr. Rogers was a Visiting Fellow at the University of Queensland, Australia (2014) and was awarded a Fulbright Specialist scholarship to Mendel University, Czech Republic (2017).  Paul is the leading researcher on the Pando aspen clone. Paul’s work on aspen ecology over the last 20 years has brought together a broad collective of scientists from around the world to develop novel research programs and management frameworks to promote understanding of aspen ecology and reveal the mysteries of the recently discovered Pando. Donations made to Paul’s organization, the Western Aspen Alliance (WAA), are tax-deductible and will go directly to restoring the Pando tree and monitoring and innovating research methods to better understand it. 

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