A quarter century of ecological recovery after the eruption, scientists find signs of nature's resilience

Studies in the years following Mount St. Helens' eruption on May 18th, 1980 have produced a number of important lessons for biologists and resource managers, according to a "Perspective" article published in Science on May 12, 2005. The article, by Dr. Virginia Dale (Oak Ridge National Laboratory) and colleagues, details how survival and succession contribute to nature's apparent resilience following the natural disaster.

When Mount St. Helens erupted in 1980, it set off an enormous avalanche, scorched forests for 500 square kilometers, and spewed out 400 million tons of volcanic ash, creating an ecological disturbance of vast proportions. Dale, whose first years of field work on Mount St. Helens were supported by Earthwatch Institute, is using this once-in-a-lifetime opportunity to discover how ecosystems respond to disturbances on this scale.

"The most significant finding was that ecological systems are so resilient," said Dale, former principal investigator of Earthwatch's The Recovery of Mount St. Helens project. "In some parts of the devastation zone at Mount St. Helens, organisms survived. Even where there was no survival, by 25 years post-eruption, the plants and animals are returning and community interactions are being reestablished."

The once lifeless-looking landscape has changed dramatically, but the effects of the eruption will influence ecological processes for centuries to come, the authors write. Their findings indicate that ecological succession on the mountain has been very complex, proceeding at varying paces for different areas. Consequently, they assert that no single succession theory provides an adequate framework for explaining change.

Other lessons from Mount St. Helens include the finding that chance factors such as time of day or year can strongly influence survival and the course of succession. For instance, because the eruption occurred on an early morning in May, survivors include nocturnal animals that were in their burrows, plants that had not yet broken winter dormancy under the snow, and migratory bird populations that had not yet returned.

The authors found that biological legacies, such as killed trees and rotten logs, can play an important role in the ecological response to a severe disturbance. Soil moisture accumulated both in depressions and on spider webs was important in trapping seeds and providing optimal conditions for seed germination.

years after Mount St. Helens erupted, Earthwatch teams joined Dale in monitoring life's renewal on a littered and muddied blowdown debris avalanche of the "Red Zone." They helped her set up permanent sampling plots and collect information on the initial plant reestablishment. Dale and colleagues have continued this work for 25 years of data on plant reestablishment, in the process changing how ecologists think of disturbances.

"Ecologists are more and more recognizing the importance of large infrequent disturbances and considering them one of the forces shaping many ecological systems," said Dale. "Managers need to plan and prepare for large disturbances. However in the aftermath of a disturbance, managers do not always need to spend a lot of money to ‘repair' a system. The resilience of nature often means that the system will reestablish without, or in spite of, human efforts."

Dale is also in the process of co-editing a book on the subject, Ecological Recovery after the 1980 Eruption of Mount St. Helens, to be published in 2005 by Springer-Verlag.

Earthwatch Institute is an international nonprofit organization that supports scientific field research by offering members of the public unique opportunities to work alongside leading field scientists and researchers. Earthwatch's mission is to engage people worldwide in scientific field research and education to promote the understanding and action necessary for a sustainable environment.

For more information, see "25 Years of Ecological Change at Mount St. Helens". V. H. Dale, C. M. Crisafulli, and F. J. Swanson. Science (308) 13 May 2005: Pp 961-962.

See also an article in the May issue of Smithsonian Magazine: "Phenomena and Curiosities: Rising from the Ashes"