Will Mount St. Helens rebuild its top before forest returns to surrounding lands?
Friday, April 2, 2010
Forest or mountaintop, which will come first?
In a colossal race between natural processes, scientists are watching geological and ecological forces race each other in real time. Some are beginning to wonder whether the mountain will rebuild its once-conical top before a forest returns to its eruption-scarred surroundings.
“It really could be a kind of competition, so to speak,” said John Pallister, a geologist with the U.S. Geological Survey in Vancouver.
From the windswept pumice plain in the barrel of the Mount St. Helens blast zone, botanist John Bishop is closely tracking the progression of plant and animal life. Bishop, with Washington State University Vancouver, would place his bet on the mountain.
“It could be that some of these areas never recover to forest, at least not before the next eruption,” he said.
Based on the length of time scientists have calculated for a closed-canopy forest to return to an area northeast of the volcano cleared by a huge blowout in the late 15th century, Bishop said it could be at least 200 years for a forest to take root in the harsh environment of the pumice plain.
If the 2004-2008 dome-building eruption had continued apace, scientists estimated at the time, it would take 160 years for the volcano to rebuild the top 1,314 feet obliterated in the eruption of May 18, 1980. The end of the latest eruption would understandably push that date back.
The May 18, 1980 blast also cleared 230 square miles of alpine forest. It’s hard to recognize from the gray, flattened terrain visible from the high vantage point at Windy Ridge, but a closer examination during a hike through the pumice plain at the right time of year reveals life returning in a riot of color - yellow dandelions, purple lupines, scarlet paintbrush.
But progress is slow.
“It’s hard not to say, ‘Great, look at all these plants,’ “ Bishop said. “But it’s also coming back slowly.”
“It’s important to understand the mechanisms and processes that lead to particular plant communities and forests that we value here in the Pacific Northwest,” he said. “Here, we’re starting from scratch.”
Using a $428,000, five-year award from the National Science Foundation, Bishop and colleagues from the University of Maryland have lately begun to focus on the effect of a nonnative type of beetle that’s invaded the pumice plain. During a field expedition at the end of July, the beetle was mainly evident from what it left behind: Dead willow branches, and piles of sawdust-like frass.
(Frass, by the way, is science-speak for bug poop.)
In the stark and open environment of the pumice plain, scientists consider the willow and alpine lupine to be “ecosystem engineers,” sparking a succession of life forms: Moths and other herbivores that eat the lupines, followed by predators such as spiders that feast on them.
Anything that constrains the growth of willows and lupines effectively short-circuits the ecological procession.
Bishop said it’s no coincidence that, beyond streambeds where alder and willow now grow in thick clumps 15 feet tall, willows on the pumice plain are usually no bigger than knee-high.
“We think if there were no beetles here, these willows would get big and thick,” he said.
The beetle is far from the only hurdle vegetation must overcome. At 4,000 feet above sea level, plants and animals must overcome winter snow and 80 inches of annual precipitation. In normal terrain, even dead plants offer the spark of life to the next generation by leaving behind basic elements such as nitrogen and phosphorous.
“Here, there is virtually no soil,” Bishop said. “When lupine dies, nutrients in the lupine don’t have a chance to be taken up by anything else. Nitrogen washes out of the dead matter in rain during the winter.”
There’s also the matter of elk.
Though Congress established the 110,000-acre national volcanic monument partly to enable researchers to see how a landscape recovers on its own, Bishop noted that elk populations are kept relatively high to satisfy hunters. Elk will nibble young seedlings right down to the nub.
That’s why Bishop and a cadre of undergrads and graduate students have constructed an elk “exclosure,” lined with a solar-powered electric fence. The idea is to compare the growth of vegetation in and out of the exclosure, which measures a little less than an acre in size.
Bishop spends many weeks during the summer camping near Windy Ridge and documenting plant life. During the week of July 24, 2007, he was assisted by WSU students Andrea Lang and Ray Yurkewycz, and Jen Balachowski, a high school biology teacher involved in graduate-level research through the University of Maryland.
“We’re watching it happen naturally,” Bishop said.
Originally published: Aug. 6, 2007