URBANA — The signs may say "no trespassing," but the half-open gates and well-worn trails through this wooded area indicate some people haven't heard.
The forest just west of Meadowbrook Park along South Race Street has been a favorite for runners, dog-walkers and bicyclists for years, officials say.
But technically the Illini Forest Plantations are a University of Illinois research area that's off-limits to the public, said Jay Hayek, Extension forestry specialist for the UI Department of Natural Resources and Environmental Sciences.
The UI wants to get the word out that the fences and gates are there for a reason, even if they haven't been all that effective.
"The public perceives it as a recreation area," Hayek said as he walked through the site Wednesday. "This is a research area. We do have a no-trespassing policy."
Officials recently discovered an elaborate "fort" built inside the woods, with second- and third-story decks. Someone also stole a pile of firewood that had been cut by the Illini Foresters student group.
The trespassers haven't harmed any research yet, Hayek said, but he and others worry about public safety and liability. Officials plan to repair holes in the fence and gates and beef up the no-trespassing signs in coming weeks.
The forest was established in the 1950s or 1960s to test how various species of trees would grow in the soil, both native and non-native, he said. Researchers take periodic measurements at the site.
But it's also become a refuge for invasive plant species, such as bush honeysuckle, brought in by birds, wild animals, people and their pets, Hayek said.
Last fall, Hayek started teaching a class on management of invasive species, taking students out to identify and remove invasive plants that account for 99 percent of the underbrush.
The students use chainsaws and loppers to cut them down, then apply herbicides to the stumps — not the best environment for recreational use, he said. One big fear is that dogs will lick the bright blue herbicide off the stumps.
The forest was planted in half-acre blocks of different tree species, and natural trails formed along the boundaries. They're obviously well-used, with deer tracks, paw prints and human footprints evident in the frozen mud.
"The vast majority of people have no idea they are trespassing, and it is a research site," Hayek said.
The main entrance at the northeast corner of the forest has a wooden sign warning the public to keep out, but the gate was open on Wednesday.
Another gate along Race Street was not fully closed, chained instead to a pole that left a gap wide enough for two people to walk through. It hadn't been moved in some time, as a tall sapling had grown through the gate. Farther south along Race, a section of fence had been torn down, providing easy access to the woods, Hayek said.
Trespassing has been a problem for years — the forest has seen its share of homeless people and "high school drinking parties," Hayek said — but the new invasive species program and the recent discovery of the fort prompted officials to act. UI Police Sgt. Tom Geis said police discovered another fort there several years ago.
The college plans to improve security with more signs and better gates along the north and east sides of the forest, the two biggest problem areas, he said. The west side bumps up against other UI research fields.
Runner Andrea Stack said she's never realized the forest was off limits and said the UI should post signs all around the perimeter if it's going to use herbicides so no one gets sick. She said there are too few natural areas left that haven't been developed or farmed.
"I think of it as an extension of Meadowbrook. I have been out there with other groups of friends in the summer before. It is nice because it is easier on your legs and feet since it isn't paved, and it has beautiful scenery and little trails here and there," she wrote in an email.
Hayek expects other complaints but urged people to use the public paths across the street at Meadowbrook Park instead.
"It's mostly for the public's safety and their pets," he said.
Many of the trees in the forest date back to the 1960s, including the Eastern white pine. Others died out, and walnuts, locusts, cedars and other trees have sprung up in their place.
The invasive bush honeysuckle, privet shrubs, bush thorn and winterberry have proliferated via droppings from birds and other animals that frequent the woods, Hayek said.
"This is an urban forest. It's a great place to study invasive species," he said.