Ten years ago, Mike Valley saw trees dying. Valley, 63, a commercial fisherman in his fourth generation on the Upper Mississippi River, fishes the backwaters, swamps, oxbow lakes, islands, swamps and floodplain forests between the high sandstone bluffs on both sides of the river. I have been fishing there for half a century. A river in Prairie du Chien, Wisconsin, where he lives.
In the spring, Valley recalled, more trees didn't shed their leaves. In patches above and below the river, many floodplain tree species, mostly silver maples but also swamp white oaks, cottonwoods, blue ash, and elms, were becoming haggard and losing their vitality. The die-off began to negatively affect his fishing. When the water was high, he fished for catfish on the flooded islands, but now there were too many downed trees to set a net. And the danger of falling trees has become a constant concern.
“The situation kept getting worse and worse,” he said. „It's really devastating.“
In recent years, scientists have been studying its causes and, in some cases, working to slow the trend, which even the most casual observer today can see. Floodplain forests are dying throughout the upper Mississippi River. From St. Paul to St. Louis, trees are disappearing, replaced in places by dense forests of invasive reed canary grass. Thousands of acres of floodplain forest have been lost since scientists began tracking changes in the late 1980s. In recent years, the rate of decline has only accelerated.
„The sheer scale of it is astonishing,“ forest officials say. “You don’t see hundreds of acres of dead trees.”
By the time scientists began monitoring floodplain forests in the Upper Mississippi, a combination of agriculture, urbanization, and river management efforts had destroyed them. almost half They noticed alarming trends, including increased flooding and decreased tree density and diversity. Aerial photographs studied since 1989 reveal that approximately 6,200 acres of lowland forest have been lost in the 330-mile drive from St. Paul to Rock Island, Illinois. In a 330-mile stretch from Rock Island to St. Louis, 5,500 acres were lost. Since then, death has only accelerated. Researchers are still analyzing more recent data, but photos show losses of 50 to 90 percent in some locations.
„It's kind of amazing how big it is,“ said Andy Meyer, a forester with the U.S. Army Corps of Engineers. “You don’t see hundreds of acres of dead trees.”
Scientists say the main cause of overall tree death appears to be flooding, which continues to worsen in conjunction with climate change. water frontier paper, spring precipitation and precipitation intensity are projected to increase across the Midwest through the end of the century. Trees that can already easily withstand a few weeks of spring flooding are now flooded for months at a time.
A silver maple in the upper Mississippi River floodplain at Fort Snelling State Park, Minnesota.
Dominic Blood/Dembinsky Photo Associates/Alamy Stock Photo
Nathan de Jager, an ecologist with the U.S. Geological Survey, said the problem is not only that the trees are dying, but that in many places they are not growing back. For reasons scientists don't yet fully understand, even areas with living trees may not have sprouts or seedlings growing beneath them. Another cause of deforestation is the increasing amount of canary grass that has grown so thick in wetlands that nothing else can survive.
Meanwhile, land-use changes are exacerbating the problem. Across the Midwest, farmers are installing tile drainage systems under fields to increase the productivity of row crops, especially corn and soybeans. This system also causes flooding, quickly sending water through pipes into nearby ditches and streams.
Floodplain forests are known to be ecologically rich. They form long passageways that allow birds and other animals to move up and down the river. The Mississippi River Valley is also one of North America's most migratory routes for waterfowl, raptors, and Neotropical songbirds. However, no one actually knows how changes in forest structure will affect birds. Increasing wetlands and decreasing forests may hurt some people and help others. Tara Homan, conservation science manager for Minnesota Audubon, said the red-cockaded woodpecker is thriving in dying forests, while the daurian redstart, which prefers understory shrubs, is in decline. The same goes for the Carolina wren.
The United States has lost 57 to 95 percent of its floodplain forests since European colonization.
Globally, floodplains are considered among the most threatened of all ecosystems. One estimate It suggested that across the United States and Europe, 90% of floodplains have been converted to agricultural land. meanwhile, the study Researchers focused on floodplain forests estimate that the United States has lost 57 to 95 percent of those ecosystems since European settlers arrived.
Of course, climate change is affecting floodplain forests around the world. Heavy rains and major flooding are occurring across central and northern Europe. kill the tree For example, along the Rhine. However, in some cases, too little water can be a problem. Like Italy, it is overgrown with oak trees and black locusts. Almost dead The floodplain of the Ticino River has suffered from years of drought. In the Cottonwoods of the American West, rivers are drying up due to drought and reduced mountain snowfall. same fate.
One of the largest intact floodplain forests in the United States is located along the upper Mississippi River in the Reno Bottoms, 11 miles upstream of Prairie du Chien. Here, the Mississippi River remains what it might have once been before the Corps began building locks, dams and levees: a wild patchwork of wetlands, lakes, islands, remote waterways and forests. Masu.
But the dead tree patches, which represent about a quarter of the forest, Meyer estimates, are relatively new, which is why the area is a focus for restoration and rehabilitation. The effort by federal agencies and conservation groups aims to improve all types of habitat, including backwaters where fish spawn and wetlands where waterfowl visit.
Restoration work at Reno Bottoms has been going on for years, albeit on a small scale. But recently, the Corps and its partners have been finalizing plans for a $37 million project that could begin this year. The project, called the Reno Bottoms Habitat Restoration and Enhancement Project, will involve dredging sediment that filled overwintering habitat for fish, constructing new islands to replace those lost to erosion, and restoring more than 500 acres of forest. There is a need for restoration or improvement. .
On a recent February morning, Meyer and Jeff Butler, an ecologist with Minnesota Audubon's Upper Mississippi River Program, met at New Alvin Landing, in a backwater project area called the Minnesota Slough. It was an unusually warm day for the end of winter, and the sun was shining brightly on the water. Geese were rustling and honking, and woodpeckers were banging on the dying trees.
“The reality is that we are not going to restore or repair all the forests that have been lost,” forest officials say.
Scientists, like fishermen, have been observing dying trees in floodplains for years. However, a series of rainy years and frequent heavy floods starting in 2016 appear to have further increased the death toll. Floodplain trees are hardy. But Meyer speculated that years of heavy flooding, which deprived the roots of oxygen, weakened them and eventually killed them.
Not far from the New Albin landing site, the two men crossed a mat of dead rice cut grass, a native species of the wetland, to a small clearing among the trees. Here, the ground was slightly lower than the surrounding forest, so the Corps plans to raise the clearing's elevation by piling up a foot or two of river sediment — enough for trees to grow. The corps hopes so. Some species, such as cottonwood, establish themselves in a location on their own. Others, such as swampy white oak trees, should be planted. The corps also wants to plant a variety of young trees in the surrounding forest, where many maples are still alive.
„We're going to work to increase the diversity of our forests and the resilience of our future forests,“ Meyer said. „We're trying to get ahead of the game by establishing other trees.“
Volunteers plant young trees in a Mississippi floodplain in southeastern Minnesota in 2019.
Anthony Souffle/Star Tribune via Getty Images
Restoring floodplain trees is no small feat. Scientists are trying to understand which trees are most vulnerable to new hydrological conditions. Why don't trees grow back in many places? And what recovery strategies are most effective? So far, they have focused on stands that still have healthy trees. Areas where all the trees have died may simply be too wet to repair.
„The reality is that we're not going to restore or restore all the forest that's been lost,“ Meyer said. „The cost would be astronomical. And we don't really know if it's sustainable in the long term.“
The 300-acre floodplain facing the western bluff, further from the river, illustrates both the successes and shortcomings of the restoration strategy. Much of this area was once rich farmland, and although regularly flooded, it still produced occasional hay crops. It was abandoned in the 1970s, but was soon invaded by canary grass. In one five-acre field, workers cut canarygrass and used machines to stir wet mud. Within a few years, cottonwoods were sprouting. However, their numbers were small and eventually they were covered by canary grass.
A diverse forest is much like the forests of the past. They are more likely to survive in the future.
Still, canary grass taught us an important lesson. Cottonwoods breed freely on floodplains without human help. But seeds need bare soil to germinate and take root. In other experimental plots, workers first killed canarygrass with herbicides and then removed the soil with tractors and discs. Cottonwoods are growing there, and canary grass is receding.
The goal here, as elsewhere, is not just to use more trees, but to use more types of trees. Workers planted cottonwoods, red birches, and marsh oaks in various locations. These are long-lived species and are a favorite habitat for birds and insects. They also planted shrubs such as buttonwood and red dogwood. A diverse forest is much like the forests of the past. But more importantly, Meyer says, they are more likely to survive future uncertainties.
A hundred meters away, Butler and Meyer stopped at a particularly promising spot. It was a grove of young swamp oaks among older cottonwoods. In 2015, Meyer and her 25 local elementary school students spent a day here planting 3,000 small bare root oak saplings. The oak tree has surpassed the canary grass, and it has surpassed all the children. Currently, they are 15 feet tall.
„This is something we want to see everywhere,“ Meyer said, clearly pleased. „We went from a monoculture of reed canary grass to a young forest.“ He stopped and looked back. “When I first came here, I found it very difficult to restore floodplain forests,” he said. “But seeing this gives me hope.”