March 17 was unusual for a St. Patrick’s Day in the Chicago area. Skies were cloudy, but in Swan Pond Park in Riverside it was an otherwise gorgeous morning — as temperatures touched 65 degrees with just the slightest of breezes.
Parents pushed kids in strollers and dogs explored the sides of the path along the river as cyclists zipped by them.
Michael Collins was in Swan Pond Park that morning for another reason. He planned to set it on fire.
“It’s a great day for a burn,” he said before donning a bright yellow fire-retardant suit and igniting a drip torch and spraying its liquid fuel mixture onto last year’s brown, dry and brittle growth.
It wasn’t the first time Collins, Riverside’s village forester, conducted a controlled burn in the area. He’d done similar burns up on the bluffs overlooking the park and the Des Plaines River.
This was first time in anyone’s memory, however, that such a burn was conducted throughout the length of the park itself, which in the past year has been allowed to revert to its natural state as a kind of prairie in a floodplain. Paths mown through the tall grasses and flowering perennials and around the low-lying area planted with native wetland reeds and sedges allow people to wander through.
“I’d like to do this every year, but sometimes the weather and timing doesn’t cooperate,” said Collins. “There’s a small window before we get rain over the weekend and we might not have a dry spell like this again.”
A more naturalistic Swan Pond Park is a concept that has taken some time getting used to, and it wasn’t necessarily planned in the wake of the comprehensive regrading of the park in 2012 by the U.S. Army Corps of Engineers after the Hofmann and Fairbank dams were removed.
But rain events in the years following have demonstrated just how much that regrading changed the park, particularly in the purposely scoured low area at the north end, where a culvert was built to drain storm and flood water from the park.
That part of Swan Pond Park essentially became wetlands, sometimes submerged for days and even weeks at a time, changing its purpose from a place where active recreation once took place to a passive one.
As a way of embracing that change and help mitigate the sogginess of the low area, in 2017 the village planted thousands of native wetlands plants, which battle for supremacy every year against aggressive invasive species like reed canary grass, phragmites (another large reed grass), thistle and teasel.
“That’s the idea behind fire,” said Collins. “It’s going to discourage those [invasive] perennials and, in return, favor a lot of the sedges and bulrushes that we want growing down here.”
On March 17, Collins systematically ignited the taller growth surrounding the sedge area near the culvert, using mown areas as firebreaks and then getting on the back side of those areas, upwind, to direct the burn back toward the already scorched patches.
“That’s called a back burn,” said Collins. “It’s a slower burn that burns more deeply and is a bit more effective, and also helps the smoke columns lift even better, in theory.”
In just a half hour or so, Collins had been able to burn a significant portion of the park’s northern end, with flames creeping slowly but steadily over the groundcover.
“That’s what we want is a nice slow burn, because the ground temperature is actually higher and that will kill a lot of invasives and favor those natives that we want,” Collins said. “So it’s not a bad thing for it to creep along like this.”
With sedges and bulrushes, the roots go so deep and that plants have been become so adaptable to fire that they aren’t harmed by a burn. For the invasive species, which tend to green up sooner than the natives, making them such tough competitors, it’s a different story.
Invasives brought from other parts of the country are not as well adapted to fire, said Collins, so the burns can destroy those species’ seeds and even the plant roots.
By late afternoon on March 17, with weather conditions remaining favorable, Collins was able to burn a majority of the park – some four or five acres, he estimated. And while the black ground left behind is a bit desolate looking, shoots of green will appear soon enough.
“It really won’t take as long as you think,” Collins said. “In fact, we’ll get rains right after this, which is why I’m kind of prioritizing this. You’d be surprised. I would say in a week or two.”