About the series “Warm Front” examines the ways that climate change is altering Minnesota and its landscape. Part 1: Spring trends earlier on the Rainy River Part 2: Invasive grasses choke birds’ habitat Part 3: Warmer lakes affect cold-water fish Part 4: Increasing rainfall overwhelms stormwater systems Part 5:: Invasive insects threaten Minnesota agriculture

HOUSTON COUNTY, Minn. – Andy Beebe and his crew move deliberately through the slough, their boots squelching in wet black silt left by the latest flood.

They push metal planters into the mud, pull bare-root seedlings from bags at their waists, and bend to tuck them into the mucky soil. Then they poke in a red flag to mark the twigs.

Straighten up. Repeat.

Soon, dozens of biodegradable red flags dance in the wind like a field of poppies.

There will be 1,000 flags by sundown — another day in an ambitious effort to restore a critical flood plain forest along the Mississippi River that has been morphing into a barren grassland with an assist from Minnesota's volatile new rainfall patterns.

For decades, the cottonwood, silver maple and white swamp oak that long reigned along the Mississippi have been struggling to regenerate, stifled by disease, rising waters that drown the seedlings and other forces. As the mature trees die out, so does critical forest habitat in one of the country's largest, most critical migration highways for North American birds.

Hundreds of bird species are affected, Beebe says. "They've been hit pretty hard."

When the forest canopy gaps and shrinks, an aggressive, sun-loving invasive plant called reed canary grass takes hold, a species that thrives in areas disturbed by fluctuating water.

If the flooding doesn't kill the young trees, the grass will. The emerald-green grass, with its broad leaves and large seed heads, can grow 6 feet tall and higher. Its dense root mass forms a thick mat that chokes out the tree seedlings — as well as native sedges, grasses and other plants that insects, pollinators, birds and a range of animals rely on.

Particularly threatened are forest-dependent songbirds such as the cerulean warbler and prothonotary warbler, as well as the red-shouldered hawk and wood duck.

Instead of a rich, diverse flood plain forest, what's emerging is a super-tough grassland, a monoculture that does not support much wildlife. The conversion is long and complex. But Beebe, a 31-year-old forest ecologist with Audubon Minnesota, says he thinks it's aggravated by the more severe rainstorms Minnesota is receiving earlier and later in the year as its climate shifts.

The Mississippi's shrinking flood plain forests are one window into the complex ways that Minnesota's familiar landscapes are changing with the arrival of a warmer, wetter future that climate change ushers in. Oak forests are moving north, lakes are thawing sooner and a monoculture like reed canary grass is finding even more hospitable places to flourish.

"It's more or less a desert," Beebe said of new grasslands. "A green desert."

Mussels and crawfish holes

Beebe has been working on the flood plain restoration since 2014, with funding from the state's Lessard-Sams Outdoor Heritage Council and a focus on strategic sections of the Upper Mississippi River National Wildlife and Fish Refuge south of Wabasha.

It's slow work.

First, crews spend two to three years killing and suppressing the reed grass — mowing it and spraying with glyphosate, a powerful but controversial weed killer that Beebe considers a necessary evil.

When the grass is beaten back, they plant flood plain trees, such as swamp white oak, basswood, cottonwood, silver maple and bitternut hickory, then spray the seedlings with blood meal to deter deer and other browsers.

On a recent spring morning they were working the Root River Tract south of Winona. The slough had been flooded for nearly two months this spring, Beebe said, and they had to wait for the water to recede.

The flood's effects were still evident: large, freshwater mussels lay scattered in the mud, probably cracked open by river otters. Mounds of crawfish holes jutted from the silt like miniature mud volcanoes in a school science project.

In a few weeks it will be 95 degrees and buggy, said Beebe, moving a few feet over to plant the next tree. A cool May day for planting was welcome. Soon they would have 3,000 seedlings in the ground — a good feeling.

The invasion of reed canary grass is a good example of why, in an environment where many factors are changing simultaneously, it's so difficult to pinpoint the impact of climate change.

Tim Yager, deputy refuge manager at the U.S. Fish and Wildlife Service, which manages the Upper Mississippi refuge, points to the Mississippi's chain of locks and dams as the bigger problem. They artificially pool the water, preventing the soil from periodically drying out so that tree seedlings can root, he said.

Increased use of nitrogen fertilizer across the Midwest is another prime culprit, according to Susan Galatowitsch, head of the University of Minnesota's Department of Fisheries, Wildlife and Conservation Biology. Galatowitsch thinks climate change certainly plays a role by aggravating floods, but the bigger driver, she said, is how the grass seizes on extra nitrogen and gets aggressive.

"I think there's a long way to go before we know how [climate change] fits into those other factors and stressors" causing the spread of canary grass, she said. "It's just one more stressor."

But Dan Shaw, a senior ecologist at the Minnesota Board of Water and Soil Resources, said he sees a clear link to climate change.

"We have pretty clear information that reed canary grass thrives where there are water fluctuations, and that many of our native plants can't handle those conditions very well," Shaw said. "It's also been well documented that we've been having some extreme precipitation. I think that combination shows a link why reed canary grass is thriving in many of these ecosystems."

Reed canary grass: A wetlands scourge

An aggressive, sun-loving invasive called Reed canary grass thrives in areas disturbed by water fluctuation. It’s been infesting wetlands across Minnesota, including critical floodplain forests along the Mississippi River, where it chokes out trees and other plants.

Crowdsourced data around Minnesota shows more reports of Reed canary grass in the northeast part of the state and the far southeast corner, near Winona and La Crosse, where the average height of the Mississippi River has risen nearly five inches in the last 20 years. Crowdsourced data around Minnesota shows more reports of Reed canary grass in the northeast part of the state and the far southeast corner, near Winona and La Crosse, where the average height of the Mississippi River has risen nearly five inches in the last 20 years.

'Major threat'

The grass itself is a subject of hot debate. Its native North American strain is devilishly difficult to distinguish from the one introduced from Europe long ago for livestock forage. In fact, they share the same Latin name: Phalaris arundinacea.

It's a "circumboreal" plant, Galatowitsch said, a species that occurs simultaneously at high latitudes in various parts of the world. Americans have bred and developed new cultivars, and Minnesota is one of the largest producers of the seed for wet forage grass.

"I've got people calling me from all across the country and they absolutely love it for their horses, their cattle, everything," said Mitch Magnusson at Magnusson Kveen Farms, a seed distributor in Roseau specializing in reed canary grass.

The DNR calls Phalaris arundinacea "a major threat to natural wetlands."

New research suggests that grass along the Mississippi River may actually be the Minnesota strain and not an exotic plant, according to Neil Anderson, a professor in the U's Department of Horticultural Science, who studies the genetics of the grass.

A native can also be invasive, Anderson said: "They don't have to be foreign and exotic to be invasive. Think of poison ivy."

Either way, the grass has infested wetlands across Minnesota, including lake shorelines, streams and rivers. It's the predominant grass in Minnesota road ditches and a major hurdle in restoring high-quality vegetation in wetlands, Shaw said.

"Nearly every project we work on has reed canary grass on it," he said. "The big question for us is, how do we maintain landscapes that provide a wide range of environmental benefits and functions?"

That's what Beebe and his crew sweat over.

"We're really trying to strategically work on big, large stretches of forest," he said, jabbing bare-root seedlings that resemble pale, gnarled carrots into the soil.

Beebe estimates that roughly half the seedlings will survive for the long term. The flooding and ice this past winter, for example, buried some of the 2014 plantings, he said.

But he'd be happy with that: It could be enough to prevent the canopy from disappearing, so birds can continue to call this part of the Mississippi flood plain home.

The goal: keep forests forests.

"You've got to keep on it," Beebe said. "Every time we plant trees, it's kind of like rolling the dice."