This ecologist has been studying Mount St. Helens since it erupted 40 years ago

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دوشنبه 29 اردیبهشت 1399 ساعت 18:24
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science mag
Charlie Crisafulli first visited Mount St. Helens 2 months after the 18 May 1980 eruption that ripped the top off the volcano, obliterated 600 square kilometers of forests, killed 57 people, and coated much of the Pacific Northwest in ash. He was a 22-year-old with an undergraduate degree in ecology, accompanying a University of Utah professor as scientists descended on the mountain. Since then, Crisafulli—now an ecologist at the U.S. Forest Service’s Pacific Northwest Research Station—has spent much of each summer taking the mountain’s pulse as life returns. He recently spoke with Science Insider about the 40th anniversary of the eruption that has defined his scientific career, and shaped people’s understanding of how ecosystems respond to such devastation.
This interview has been edited for clarity and brevity.
Q: What did you see the first time you set foot on Mount St. Helens?
A: We were all absolutely blown away by the intensity and extent of the disturbance. We began setting up plots primarily looking at small mammals, birds, and amphibians. Our design was to take advantage of the natural experiment that volcano created because there were different intensities of disturbance.
Q: Are you still monitoring some of those same plots?
A: There’s pieces of rebar that form the boundaries of plots I pounded in when I was 22 years old. I’m 62 now, and I’ve returned to those plots every year. And so for many of these things, there’s a tremendous amount of attachment to them.
Q: Are there any particular places you recall seeing on that first trip?
A: Not only places, I’m talking about individual plants. As you approach the Pumice Plain [an area close to the eruption covered in volcanic debris], we looked up and there were a couple of surviving plants. We started trapping there. Sure enough, the first night we caught a deer mouse that close to the crater, just a few miles away. I saw this one sprig, I went up to it, and it was a parsley fern. Every spring since then I have gone and said hello, greeted that same exact plant every year for 39 years.
Q: What is the place like now where you found that plant?
A: Today the entire slope is green. There’s woody shrubs like green alder and willows and mountain ash, occasional Douglas fir popping up through the shrubs, and then there’s a dense layer of huckleberries. And then beneath that, you know, a series of forest understory herbs and mosses. It’s a thicket.
Q: What are some of the key scientific insights from the work?
A: The initial impression was that nothing could have survived this level of disturbance and that the regeneration of the area’s ecology is going to come from the edges and from distant source populations. Instead what we found is that, in some 90% of the landscape, the rule was survivorship, albeit at greatly reduced numbers and in isolated refugias. The single most important factor governing the regeneration was those biological legacies. And that was not something we anticipated.
What we’ve learned is that incredibly complex, early seral habitats [woodlands dominated by shrubs and grasses] developed that are food rich, because they largely are supported by herbs and flowering plants, as well as shrubs. Even from space today, Mount St. Helens jumps out at you as this huge patch of something that’s different. What you’re looking down on is a landscape that supports a tremendous biomass of neotropical migrant birds, such as yellow warblers, orange-crowned warblers and willow flycatchers, and very diverse small mammal communities that are fundamentally different from adjacent old growth forests.
Q: Has the work at Mount St. Helens informed understandings about these processes in other places?
A: When a volcano starts acting up in Chile, or in Japan, or Iceland, or New Zealand, we’re often contacted to say, “Help us anticipate what’s likely to happen.” The question I had was: To what extent are these lessons at Mount St. Helens general across different volcanic settings? What we have seen is strikingly similar patterns of ecological response.
In all cases, what we found is nutrient-impoverished volcanic material. And that’s one of the biggest obstacles [to ecological recovery]. There seems to be always heroes at these volcanoes that play critically important roles. At Mount St. Helens it was species such as lupine and alder. They had a special association on their roots with bacteria that produce nitrogen. So they were able to exploit these landscapes, and in doing so, they modified these sites and facilitated the colonization of many other plants and animals.
The pocket gophers survived under the volcanic deposits, and later would go on to burrow in the old forest soil. It mixed soil with volcanic tephra, creating this great place for plant growth. Other examples are elk, willow, and the American beaver. These the heroes of Mount St. Helens. We see organisms playing the same roles at other volcanoes. In the case of Surtsey [in Iceland], it was seabirds. And when you go to Krakatoa in Indonesia, it’s fruit-eating bats.
Q: Do you have big unanswered questions?
A: Lately, I’ve been monitoring large mammals through a network of cameras. Last year, we documented that American black bears and mountain lions are regularly using the Pumice Plain, the most hard-hit areas. What is the influence going to be on the biota now that large apex predators are back in the system? We haven’t done a lot of work really looking at the interactions between aquatic and terrestrial ecosystems, and those boundaries are probably incredibly important. And then another question to me is the fact that the whole North Fork Toutle [River] ended up regenerating into red alder stands, and the trees only live till 40 or 80 years old. So what’s going to be the next stage?
Q: What are you going to do on the 40th anniversary?
A: Well, I almost always take that day and I go as deep into the blast area as I can, and I spend the day reflecting on that remarkable day back in 1980 and memories of places out there. I visit some of them and just kind of sip up everything that it has to offer.
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This ecologist has been studying Mount St. Helens since it erupted 40 years ago

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