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The Science of the Pando Tree

Wildfire in Aspen Landscapes

Paul C. Rogers | Director | Western Aspen Alliance

June 2021

Wildfires play an important ecological role in the western United States in both forest and grassland communities.  Fire is nature’s way of rejuvenation and certain plants rely on periodic burning.  However, popular media often paint a negative picture of wildland fire because homes may burn and, in rare instances, people may be injured or even killed.  Aspen forests, however, often benefit from burning as they respond very well to open conditions following such events.  On balance, forest fires benefit some species while they harm others.  Across large landscapes a mix of forest species of various ages—some recently burned, some thriving for centuries—is thought to promote the greatest diversity of plants and animals.

wildfire in aspen landscapes s

Wildfires play an important ecological role in the western United States in both forest and grassland communities.  Fire is nature’s way of rejuvenation and certain plants rely on periodic burning.  However, popular media often paint a negative picture of wildland fire because homes may burn and, in rare instances, people may be injured or even killed.  Aspen forests, however, often benefit from burning as they respond very well to open conditions following such events.  On balance, forest fires benefit some species while they harm others.  Across large landscapes a mix of forest species of various ages—some recently burned, some thriving for centuries—is thought to promote the greatest diversity of plants and animals.

Aspen has conventionally been thought of as “fire dependent,” meaning that it requires occasional flames to flourish. The quick-sprouting root system of an aspen clone (asexual reproduction) rapidly regenerates after all types of disturbance (i.e., landslides/avalanches, insects, disease, drought, tree harvest) including burning. Moreover, recent discoveries of greater genetic diversity in aspen communities and common occurrences of seedling (sexual reproduction) establishment following fire is leading practitioners to question traditional aspen management.  Fire suppression during recent decades is thought to be partially responsible for long-term aspen decline, however several experts have questioned this assertion.  Likely, there are several causes for the lack of fire, most notably a relatively moist 20th Century that favored expansion of conifer trees in some aspen forests over this period.  Stable (nearly pure) aspen is much less conducive to wildfire or prescribed burning; renewal in these forests is dependent on more continuous, low-level, tree mortality and regeneration.

Use of fire to restore aspen is a viable means of reducing conifers and promoting aspen suckers and seedlings where these tree species co-occur.  When disruption of fire cycles due to past fire suppression is evident, using fire to restore aspen is a common response.  Some managers favor a combination of harvest and burning, particularly where the possibility of escaped fires can damage property.  Use of fire in pure aspen stands, such as those exhibited at Pando and across the Colorado Plateau, is generally thought to be inappropriate as there is little ecological precedent for widespread fire impact to these forests.  In fact, a recent study found that there was only modest occurrence of fire within the present-day Pando landscape while aspen communities remained dominant there over the past 8,900 years!

Native Peoples of North America used fire in some areas to modify conditions, however there are wide discrepancies as to the extent of these practices.  It is probably safe to assume that areas less traveled, or at distance from established settlements, felt less impact of Native-initiated fires than those in proximity to human populations.  Moreover, there is a general gradient of susceptibility of forests to flames: those at lower elevations are more flammable and burn more frequently than high-elevation forests which would also be farther from valley settlements.

wildfire in aspen landscapes

In summary, aspen in the Fish Lake Basin near Pando, would be expected to burn more if there is ample conifer growth mixed with aspen.  Fires may be initiated from both natural causes and human activities.  Sometimes managers use fire to promote ecological restoration. Where conifers are generally absent and aspen dominates, we wouldn’t expect to see large fires or use fire as a management tool.  Understanding where fire occurs and where it is appropriate can benefit forest stewards and users alike!

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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