Fred Swanson, a Forest Service geologist at the Pacific Northwest Research Station in Corvallis, Oregon, says scientists surveying the devastated landscape following the 1980 eruption were struck by how dead tree snags and fallen logs—so-called “legacy structures”—provided invaluable refuge for the surviving plants and animals while simultaneously serving as base stations for colonizing species. “This dead biological legacy seemed to be performing a wide variety of ecological functions in terms of helping survivors make it through,” says Swanson.
According to University of Washington forestry professor Jerry Franklin, who surveyed the blast zone for the Forest Service in the early 1980s, these revelations led to a paradigm shift in Pacific Northwest logging techniques. One practice that emerged, says Franklin, is called “variable retention harvesting,” which instructs loggers to leave as much woody debris on the ground as possible to aid natural restoration. The technique was first put into widespread use as part of 1994’s landmark Northwest Forest Plan, which covers 24 million acres.
Charlie Crisafulli, staff ecologist at Mount St. Helens National Volcanic Monument, adds,”Just as we learned at St. Helens, if you replant a denuded site with a few native species, the native biota comes back markedly faster.” Crisafulli also applied the lessons about leaving legacy structures in place to restore biodiversity on Wyoming coal mine sites that had previously been left for dead.
A common thread running through discussion of Mount St. Helens is gratitude toward 1982’s predominantly conservative Congress for establishing the 172-square-mile national monument. “Scientists had a very strong role in the recovery of the region, and Congress listened to them,” says ecologist Virginia Dale of the Washington Native Plant Society.
Scientists say they still have a lot to learn about ecology at Mount St. Helens. The recent re-awakening of the volcano, dormant since the 1980s, may jeopardize some of the research, but in the interim scientists are learning all they can.