'Like a gut punch': Iowa State professors raise issue with trees felled for flood mitigation
Iowa State professor Janette Thompson said she had a visceral reaction upon seeing a riverside forest destroyed along Ioway Creek.
"I drove over the bridge and I just thought I was gonna lose my breakfast," Thompson said. "It was like a gut punch."
The city felled trees along the Ioway Creek, near the Duff Avenue bridge in Ames, this spring as part of a $4.9 million flood mitigation project 10 years in the making.
While the city plans to create wetlands in the area, Iowa State Natural Resource Ecology and Management professors Thompson, Timothy Stewart and Michael Rentz say the project removed established habitat incomparable to anything manmade.
The removal can impact wildlife in the area and takes away key functions trees provide along a river, the professors say.
“The city has a responsibility to maintain public safety obviously, and flooding has been a big problem,” Thompson said. “We don’t really want to put anyone on the carpet. They’re respected colleagues."
But, “this idea that the project would provide valuable habitat, from the perspective of people who have studied natural habitats their entire careers — we were mortified,” she said.
For the city, tree removal was a necessary step in a project to reduce flooding — a reoccurring issue in Ames.
Major flooding along Ioway Creek and South Skunk River occurred nine times since 1965, twice in 1993. The flooding of 2010 led to the Ames Flood Mitigation Study, completed in 2013.
In 2018, FEMA awarded the city $3.75 million toward the project, with $1.2 million contributed from the city's budget.
The project raised concern in the community after trees were felled in the area, ahead of April 1 so endangered species would not be roosting in the trees. An environmental report completed for the project found Indiana bats and northern long-eared bats, two protected endangered species, could habitat the area.
Ames municipal engineer Tracy Peterson the safety in the community from flooding was prioritized.
“We do have those environmental reports and it was, ultimately, the safety of the community,” Peterson said. “Not everybody supports it and I realized that there are different perspectives.”
A different type of habitat, pocket wetlands, will populate where the trees once stood.
The use of this type of vegetation will reduce high nutrients and suspended solids, Peterson said, which have eroded in the past, causing sanitary sewer truck main breaks. The changes will also prevent high bacteria levels.
"It is not our intent to have compared the mature forest ecosystem to the native vegetation being planted and wetlands being created as part of the flood mitigation project," Peterson said.
Thompson, Stewart and Rentz say this type of forest is part of a declining resource in Iowa that cannot be replaced.
“Clear-cutting is never a good thing. That’s never a natural way to manage any forest,” Stewart said.
It would take century to replace riparian forest, professor says
Wooded areas make up a small portion of land in Iowa, though there are 1 billion trees across the agricultural state. Iowa felled 192,000 acres of trees from 2009 to 2013, adding 95,000 acres of woodland back, according to a 2016 federal report.
Riparian forests, which are forested and wooded areas along a natural water source, serve many purposes, including promoting water quality, helping with flood mitigation and aiding fish habitat.
They shade the water, keeping the temperature low which provides more oxygen so more fish can populate the area, Stewart said. The forests also retain the soil in place which reduces the sediment and pollution going into the water, and even when trees fall into the river, it creates a habitat for fish.
“A matured gallery forest in central Iowa is such a valuable resource,” Thompson said. “They provide some of the very flood mitigation functions that were being sought in this project.”
The roots soak up water, leaves slow the speed with which rainfall hits the ground and tree trunks can slow down water flow, she said. Peterson said while trees provide flood mitigation, they cannot keep up with the pace of rapid flooding.
The professors also expressed concern with the wildlife impacted in the area, especially with endangered species habitat in the area.
“Habitat is specific. There’s no such thing as wildlife habitat. There’s cardinal habitat or pheasant habitat and they’re not necessarily the same,” Rentz said. “It appears what (the city wants) to put in is not a habitat we are in short supply of.”
Story County is in the summer range of Indiana bats and northern long-eared bats. Indiana bats enjoy small stream corridors with well-developed riparian woods, according to the environmental report, and northern long-eared bats make their home in upland forests during late spring and summer.
Both habitats are present in the impacted area.
Fourteen species with special concern — pipevine swallowtail, purplish copper, wild indigo dusky wing, among others — had habitats observed in the area.
None of the species were observed, the report says, though "no species-specific studies were conducted" aside from habitat observation.
Even if the trees were removed before the bats could roost, the loss of habitat could still impact their survival. Stewart said if habitat declines, the species population will decline as well, not necessarily proportionately to the amount of habitat lost.
“We’re still eliminating their habitat. We’re still indirectly killing them or their reproduction isn’t as effective,” Stewart said. “They took the trees down in March like that’s going to solve that problem. That doesn’t solve that problem. I appreciate that they didn’t fell the trees when the poor bats were in the trees, but there were other things in those trees.”
Stewart said squirrels, owls and foxes lost their habitat as well, the latter two serving an important purpose of reducing rodent population.
For this riparian forest, Thompson said the damage is done. She did not find out about the project until reading about the already-completed tree removal in the Tribune.
"Maybe we can be paying more attention," Thompson said. "I think it's incumbent on people who are going to do this kind of work to reach out to experts ... In this case, the damage is done. But one hopes in (the) future they wouldn't do anything of the sort ever again."
However, the city did consult the Iowa Department of Natural Resources and the environmental study was completed.
“We all want to continue planting trees and protecting trees,” Peterson said. “We have continued to flood so severely in the South Duff area that this is to provide that capacity to improve safety.”
Still, Stewart said any attempts to create new habitat can't replace what was lost.
"It would take, if this was to work out fine, 100 years for that forest to be replaced and it could probably never be replaced," Stewart said. "You do something in a few minutes, and we're talking a minimum of a century if we want to replace it."