On a switchback overlooking the Missoula Valley, Robert Pal knelt down and pulled a Jim Hill mustard plant – aka tumbleweed – from the arid soil alongside the trail.
The plant’s stems included tens of thousands of seeds waiting to burst forth and proliferate. The European invader will be hard to eradicate now that it’s here.
“Plant invaders have the capability of taking over and they can decrease plant diversity once they do,” said Pal, a visiting professor at the University of Montana. “When you look at what causes the most species extinction on Earth, biological invasion ranks second behind habitat destruction.”
Pal, a botanist and ecologist from the University of Pecs in Hungary, recently arrived at UM on a Marie Curie Fellowship. He stepped off the plane eager to study the mysterious flora of western Montana, doubtful he would have much luck in naming what he saw at a glance.
But on a recent hike of Mount Sentinel, not far above the greening UM campus, Pal found it easy to identify the plants he knew in Europe. His surroundings looked too familiar – the meadow foxtail, pale madwort, creeping bellflower and common mouse-ear chickweed, for starters.
“I was very surprised,” Pal said. “I thought I would know nothing of the flora. These are European invaders.”
Pal has since identified 99 invasive species on Mount Sentinel alone. What looks common to most hikers alerts Pal and researchers at the Callaway Lab at UM to a larger problem – invasive plants go beyond spotted knapweed and leafy spurge, and they’re spreading.
“A lot of what we’re doing now is trying to quantify and compare the abundance and impact of these invasive species on native plants, not only here but in their native range,” said professor Ragan Callaway with the Division of Biological Sciences. “We have worse invaders in the valley than knapweed.”
Callaway and Pal believe knapweed was identified in the Missoula Valley sometime in the 1970s, suggesting it’s a recent invader. Leafy spurge has also moved in. Over a few decades, it has grown to cover vast tracts of land, especially in the North Hills.
“It’s a concern if you’re a rancher and the plants provide poor rangeland,” said Callaway. “Things here don’t eat knapweed and spurge.”
Pal’s list of invaders runs well beyond knapweed and spurge. Of the 99 invasive plants he has identified on Mount Sentinel, at least 48 are annuals. Eleven species arrived in the Missoula Valley as ornamental plants and another 11, he said, were planted intentionally to provide ground cover and fight erosion.
However they made their way across the Atlantic Ocean to western Montana, their abundance is becoming clear, though their long-term impacts remain uncertain.
“If you look at the first few meters off the trail, basically you don’t see anything else, just weeds from Europe,” Pal said. “This would be cheat grass and that’s crested wheatgrass. It was brought here on purpose to stabilize unstable surfaces.”
At the switchback, Pal conducted another count. With little more than a glance across a five-meter area, he identified 10 European invaders, including yellow salsify, Dalmatian toadflax, stickwilly, prostrate knotweed and Jim Hill mustard.
It’s not a surprise when Pal talks about the North American plant invaders found in Europe. The giant goldenrod is to Hungary what spurge is to Montana, meaning the problem crosses continents in both directions.
Pal estimates that 25 percent of the plants on Mount Sentinel are invasive. And while it may be too late to control some invaders in Missoula, better gardening practices, more cooperation from home garden centers, and general awareness could help, he said.
“The number of European invaders we’ve identified is really amazing, as the total number of exotic weeds in Montana is only about 400 species,” Pal said. “Some of these invaders already cause serious problems, and some might only explode in the coming years.”