State-threatened Sedge’s Unusual Biology, Habitat Protection Helps it Survive

Photos by Andrew Hulin.

Illinois Department of Natural Resources (IDNR) staff members Joe Kath and Andrew Hulin found an abundance of the state-threatened Hall’s bulrush (Scheonoplectus halli) during surveys in 2019. They even found new populations based on biological models Hulin, an IDNR Geographic Analyst, created.

Two years later botanists and other IDNR employees checked places where the plant had been seen in the past. On that late September 2021 day, they didn’t find any.

That doesn’t mean it’s gone, said Kath, IDNR Endangered Species Program Manager.

“You may not see this plant for 5 to 10 years, or perhaps even longer. Then if you’ve got the right conditions, all of a sudden, they’ll be back,” Kath said.

The plants have hardy seeds that can remain in the soil or seed bank for as much as 25 years.

“They can stay dormant and when the right conditions exist, they come out and reproduce,” said Phil Cox, IDNR plant ecologist, who is recovery lead for the threatened bulrush.

The IDNR is working to preserve this rare Illinois species where a stronghold remains in five counties—Mason, Menard, Cass, Morgan and Tazewell, with outlier populations in Kankakee and Alexander counties. A small percentage of the populations have been found in or near the edges of agricultural fields, according to Kath, with the rest on state-owned or other private property.

Hall’s bulrush currently occurs in 11 states. The U.S. Fish and Wildlife Service was petitioned to list the plant as federally threatened or endangered, but after a thorough data review in May 2021, they determined listing was not warranted, Kath said.

Hall’s bulrush isn’t a showy plant, and it is actually a sedge, not a bulrush. This sedge spreads from its stems off to the side instead of upward. The flowers are tan and only about 2 centimeters wide, making it tricky to find among all the other vegetation.

But in late September, when the sedge has gone to seed, it can easily be identified by using a magnifying glass to view the achenes, which are fruits and seeds of sedges.

“With the Hall’s bulrush, the achene is round with ridges on it and it’s flat on one side,” Cox said.

Kath said a fascinating part of this plant’s biology is that the state-threatened Illinois chorus frog, typically found during spring surveys, is often in habitat that favors Hall’s bulrush.

Both species require edges of ephemeral ponds located in shallow depressions, often with sandy soil.

Historically, the bulrush grew in wet prairie and very shallow wetland areas that may hold a small amount of water, but not deep, and moist sandy soils.

“These habitats have mostly been converted to agricultural fields, but some seeds remain dormant beneath the ground,” Kath said.

“The seed can hide out for many years in the soil,” said Cox, who thinks the rain patterns in the 2021 growing season may have played a role in keeping the bulrushes from emerging in the areas they checked.

“It seems like the years they do best is when a large aquifer in central Illinois is charged,” he said.

Kath added that it’s possible the plant is more widespread than biologists think because it’s so small and easily overlooked.

Hulin created a spatial habitat model with a computer to ascertain where Hall’s bulrush might be growing that the IDNR doesn’t know about. Historically, locating rare species, which often occur within a narrow range of habitat characteristics that may be nearly imperceivable in the field, is a labor-intensive process. Complicating the search for Hall’s bulrush are its diminutive size and sporadic growth habit. The use of computer habitat models improves the efficiency of the field work by pinpointing the locations of sites containing ideal habitat characteristics.

“He took certain habitat characteristics of the species and plugged them into a computer model he designed,” Kath explained. “The components of the species habitat used were intersections of depressions on the landscape combined with agricultural land use and sandy soils.”

“He also plugged in wetlands that were identified under the National Wetlands Inventory maps,” Kath added. In addition, Hulin also logged known areas where Illinois chorus frogs have been found.

Using the habitat model, Hulin created a map identifying locations where the plant might exist, but no surveys had been conducted.

“In October 2019, we gathered a group of biologists and hit the field,” Kath said. “We found Hall’s bulrush at 13 locations, six places where they had not been documented before. Some locations contained hundreds of plants, others perhaps less than 50. What’s really exciting is that the six undocumented locations were based solely on the habitat model.”

“We found a lot of these plants in small depressions within harvested corn fields, soybean fields, shallow farmed wetlands and areas that are flat with sandy soils,” he said.

Some options to protect and expand the bulrush’s range include work with private landowners to educate them and provide suggestions on how to maintain habitat pockets for the bulrush, as well as the Illinois chorus frog.

“Because it’s so long-lived in the seed bank and we have this habitat model, we can apply it on a larger statewide basis to check other counties where it might be growing,” Kath explained.

“Future purchase of certain properties with the right habitat along with seed transfers also could be considered,” Cox said.

It all comes down to habitat. The future for this plant as well as many other species that rely on moist sandy soils and shallow depressions hinges on preserving those areas.

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Sheryl DeVore writes environment and nature pieces for regional and national publications and has had several books published, including “Birds of Illinois” co-authored with her husband, Steven D. Bailey.