The evergreens will be first, yellowing needles signaling a dying tree.
The cottonwoods and box elders will hang on a bit longer, but they, too, will start to drop their leaves as the lack of oxygen begins to starve them.
People along the Missouri River have been focused for the last month on the immediate needs of sandbagging, evacuating, finding places to live, stripping their homes, plugging drains, monitoring pumps.
But as the summer goes on and the waters stay high, public groups must start planning for the time when the water recedes and leaves behind it acres and miles of dead vegetation and thousands upon thousands of dead and dying trees all along the river.
The tree-kill problem is going to be gigantic, said ElRoy Haadem, the Burleigh County NDSU extension agent.
Haadem said he has been asked by people who wonder what will happen to the tree-lined river that Bismarck-Mandan is accustomed to seeing.
Some trees can stand a degree of flooding, but weeks of waterlogged roots cuts off their oxygen, Haadem said.
Evergreens are the first to go, he said, followed by the deciduous cottonwoods and box elders.
Once, pre-dam, the river flooded periodically, spreading cottonwood seeds and nourishing the seedlings and young trees, Haadem said.
But since those were early spring floods, trees were still winter-dormant with minimal oxygen needs, said Jackson Bird, the Bismarck city forester.
This flood is during the trees’ growing season, when they need oxygen to keep producing leaves, he said.
Haadem and Bird are planning to meet with forestry, government and natural resources groups in July to start working on a plan to deal with the aftermath of the kill-off.
Concerned groups would include the state and U.S. Forest Service, soil conservation districts, county agents, the Natural Resource Council and Lincoln-Oakes Nursery staffers, weed boards, county and city government agencies, North Dakota State University forestry experts and more, Bird said.
The cleanup will be massive, Haadem said. Vegetation and lawns will die. Sediment from the river will be left aground and will need to be analyzed to see if it must be removed from lawns or can be left.
And backwaters, where the current is slow, may see invasive species such as saltcedar, brought in with the current and popping up where they’ve never been seen before, he said.
There is no logging entity in North Dakota to remove all the dead wood, he said. It will affect a huge swath of land up and down the Missouri — all the counties, public and private property, all the way up to Williston, Haadem said.
“It will be gigantic,” he said.
Homeowners will lose such flood-intolerant tree species as spruces and crab apples, and even tougher species such as cottonwoods, box elders, American elms, silver maples and bur oaks will sustain damage after what will likely be months in standing water, Bird said.
“And who knows what (will be) floating in the floodwater?” he said. There may be chemicals that can change the pH of the soil in certain pockets.
The longer the water stands, the more potential damage, Bird said.
On Parks and Recreation land, for example, Pioneer Park trees already are showing some browning and trees in Sertoma and Riverwood are underwater.
Thousands and thousands of trees will be lost, Bird said. Some will die immediately; for others, it will be a slow dying over some years.
Symptoms of tree damage include early fall coloring, dropping or stunted leaves and brown or gray mottling on the edges, he said.
If whole sections of a tree’s canopy are dying off, there’s no hope for the tree, he said.
Dead and damaged trees with decaying roots systems can become unstable, at risk of toppling over in high winds. They will also be vulnerable to secondary weakening from invasion by fungal spores and insects, Bird said. Removing unstable trees from public recreation areas would be a priority, he said.
For years to come, the tree canopy along the river from Garrison Dam to Pierre, S.D., will be very different from the one people are used to seeing, Bird said.
With the dead understory vegetation and the dead and drying trees, there will be much more tinder for fire as well, he said.
Reforestation will be a multi-year effort, Bird said. And bringing the canopy back to maturity will take a lifetime for some trees. The large cottonwoods, for example, will take 50 to 100 years to mature.
The job is daunting. Bismarck has only four full-time arborists, and finite resources, Bird said. Perhaps logging experts with portable sawmills will come in to handle the volume of trees that need to be removed, he said.
Though trees submerged throughout the summer are lost, he said, people might try to salvage some of those on higher ground by fertilizing them and aerating the soil. Most of the tree’s oxygenation takes place in the top 18 inches or so, “so that might help,” he said. “Anything’s better than nothing.”
“The sooner the better, to start planning,” he said.
For a publication on the effects of flooding on trees, visit http://www.extension.iastate.edu/publications/SUL1.pdf.
(Reach reporter Karen Herzog at 250-8267 or email@example.com)