Dan Wheat/Capital Press
WENATCHEE, Wash. — Management of invasive plant species is still too much like surgery by bludgeon instead of scalpel, says Dean Pearson, research ecologist at the U.S. Forest Service Rocky Mountain Research Station in Missoula, Mont.
“We’re getting good at taking out the target weed but not much good beyond that. Better restoration tools is where the big need is right now,” Pearson said in his keynote address at the Washington State Weed Association’s 67th annual conference at the Wenatchee Convention Center, Nov. 1.
Pearson said he’s found 168 studies of the management of invasive plants with only 38 of those looking at what happened beyond the weed.
“In those 38, we found 96 percent suppressed the target weed, so that’s success. But the primary response to the control was secondary invasions, 89 percent of the time by a noxious invasive weed. That’s not what we want to see happen,” he said.
The key in handling invasive plants with herbicides is aiming to get to a place of surgical precision with minimal disturbance to the ecology, or pushing it in the right direction, he said.
Broadcast reseeding is the most cost effective restoration tool but effectiveness is like a lottery because weather plays a big role, he said.
Invasive plants can alter an ecosystem for a long time, Pearson said. He showed pictures of a Missoula hillside in the early 1970s with Balsamroot, Lupin and Paintbrush and a picture of the same area drastically altered by Knapweed 30 years later.
Loss of the perennial forbs of Balsamroot, Lupin and Paintbrush affected pollination, meant less food for elk and reduced butterfly larva and grasshoppers that are food for Chipping sparrows, he said. Study showed songs of the Chipping sparrow changed, he said.
“They were telling us Knapweed is bad,” he said.
When Knapweed overran perennial forbs in the Flathead Valley north of Missoula, there was an explosion of spiders and a reduction of spider prey to the point that the prey’s prey increased, he said.
Lots of things can alter the trajectory of an ecosystem and management of invasive plants can make things better or worse, Pearson said. Original equilibrium is seldom, if ever, achieved but a goal can be to get as close as possible with minimum damage, he said.