Battling a wetland weed.

Byline: Scott Maben The Register-Guard

From a distance, the sweep of tall grass around Fern Ridge Lake paints a picture of nature thriving in unspoiled habitat.

It's a deceptive image. The reed canarygrass is a tenacious invader that's driving out dozens of species of native plants and animals across thousands of acres of wetlands on the west side of the Cascades, scientists say.

"We call it a weed," said Mandy Tu, a botanist with The Nature Conservancy. "It completely takes over our native wetlands."

It's probably the exotic species doing the most to undermine wetland restoration and conservation work in the region, Tu said.

But reed canarygrass is not invulnerable. New research at Fern Ridge points to several effective methods of eradicating small patches of the exotic plant and significantly reducing large infestations of it.

At the Fisher Butte state wildlife area on the east end of the reservoir, The Nature Conservancy and the Army Corps of Engineers have teamed up to test how reed canarygrass responds to 18 combinations of mowing, tilling, shading, burning, flooding and herbicide spraying.

Researchers are in their third year of controlled tests on 144 small plots as well as several larger experimental treatments. Similar work is under way at a wetland 20 miles northwest of Portland.

It's the first comprehensive study of how best to control reed canarygrass in natural areas of the Northwest without seriously disturbing surrounding habitat, Tu said.

The project includes varying the times of year when plots are treated. In some places, researchers spread native plant seeds after a treatment to compare the response to natural regeneration from seeds still present in the soil.

The research on the test plots will formally conclude at the end of this year, but preliminary results show that certain combinations - tilling followed by flooding, for instance - repeated over several years are the best ways to combat reed canarygrass, Tu said.

"One of the biggest findings from this research is that you have to do it several years in a row," she said.

And on large tracts where total eradication is unlikely, ongoing maintenance is necessary to keep the grass from bursting out of control again, Tu said.

The findings should prove invaluable to public land managers and private property owners who are struggling to head off the constant march of reed canarygrass. Many of them resort to herbicides - a practice The Nature Conservancy hopes to see scaled back in favor of mechanical treatments.

The Corps of Engineers uses herbicides on a limited basis at Fern Ridge now.

On smaller scales, others try to smother the grass - a technique replicated at the study site using plastic shade cloths. But that also denies water and sunlight to desirable plants.

"If there's nothing you want to preserve, it's a great low-maintenance method," Tu said.

Reed canarygrass, native to Europe, was planted widely in the Pacific Northwest and northern Midwestern states starting in the early 1900s to control erosion and provide pastureland for cattle.

The Northwest variety was bred to grow fast and tall, surpassing 6 feet. It spreads prolifically through self-seeding and root shoots, and where it's thickest, it leaves no room for anything else to grow.

"It out-competes all native vegetation, so you don't see anything else out here," Tu said, standing in a dense stand of reed canarygrass jutting over her head. "This is pretty much a monoculture."

Native amphibians, rodents and birds tend not to forage or nest in areas where the exotic grass has taken over, she said.

The damage around Fern Ridge, a 10,000-acre project managed by the Corps of Engineers, is compounded by the presence of rare plants, including three species that the federal government has listed as threatened or endangered.

"It truly is a threat to the rare species and native prairie here," said Wes Messinger, a Corps of Engineers botanist based at Fern Ridge Lake.

In addition to crowding out native plants, reed canarygrass can drastically alter the function of an ecosystem, researchers said.

The plant's massive root systems and the dense layers of dead and decaying grass from previous crops build up the surface of a wetland, eventually drying it out.

As a result, seasonal water flows become diverted or blocked, in turn wrecking the habitat and upsetting flood control and water purification, Tu said.

"These ecosystem changers are the invasives we're most concerned about," she said.

In one area, the Corps of Engineers and the state Department of Fish and Wildlife ran a large disc tiller back and forth across the land last fall, then flooded it through a network of dikes and channels that control water flow around Fern Ridge.

What has re-emerged, Messinger said, is a native wetland community of plants and animals. Ducks, Canada geese, egrets and white pelicans found the open water inviting last winter. Cattails, water plantain, spike rushes and wapato are among the native plants that are springing back to life this year.

And little green frogs can be spotted on the water's edge, doing their best to avoid predatory bullfrogs, another non-native species.

After two consecutive years of such treatments, the reed canarygrass problem appears easily manageable with occasional spot treatments, Messinger said.

"This is sort of a maintenance commitment we make to the habitat," he said. "You can't really treat anything and walk away from it."

The study was slated to end this year. But Tu said she expects to continue monitoring the test sites to see how well native plants return to treated areas - and how quickly reed canarygrass reinvades.

As for the Corps of Engineers, the agency wants to expand its treatments, mostly using tilling and flooding, across the heavily infested Fern Ridge wetlands to give native species a shot at reclaiming their territory, Messinger said.

CAPTION(S):

Cudweed sprouts next to dead reed canarygrass at a Fisher Butte test site where herbicide is used on the invasive grass. H a b i t a t r e s t o r a t i o n