Plant survey reveals dozens of non-native invasive species thriving in Ohio

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A new botanical study from southwestern Ohio has found that invasive species introduced to the United States over the past century are crowding out many native plants.

Biologists from the University of Cincinnati trace two exhaustive surveys conducted 100 years apart to see how Queen City’s plant diversity has changed over the past two centuries. They focused their attention on the undeveloped parts of the cemeteries, the banks of Mill Creek and the public parks that have remained protected from development for the past 200 years.

The study, titled “The Rise of Non-Native Plants in Forested Natural Areas of Southwestern Ohio,” was published in June in the journal Ecological restoration.

UC’s latest survey follows in the footsteps of Cincinnati botanist Thomas G. Lea, who surveyed plants in Cincinnati between 1834 and 1844. During that time he built up a herbarium of specimens that went to l Philadelphia Academy of Natural Sciences. Lea identified some 714 species before she died in 1844. Her work was published posthumously in 1849 by her brother.

A century later, famed UC botanist E. Lucy Braun retraced Lea’s path, conducting a second plant survey in Cincinnati that found over 1,400 species in her 1934 study published in The American Midland. Naturalist. She relied on Lea’s meticulous notes to retrace the places he visited, many of which had been turned into homes, roads or apartment buildings over the decades.

UC biologist Denis Conover and co-author Robert Bergstein traced Braun and Lea’s footsteps in southwestern Ohio to places where city development has not paved natural areas. They have found that many species purposely introduced as landscape plants flower in the wild.

“The spread of non-native invasive species in forested natural areas of southwestern Ohio threatens the survival of native flora and fauna. Efforts by park managers and volunteers to control invasive plant species are have become an important part of their duties. This effort will be needed in perpetuity and will be costly both financially and temporally due to the collateral damage caused to native plants, wildlife and humans by the extensive use of herbicides, chainsaws and other mechanical equipment,” the study concludes.

Horticulturists introduced most non-native plants from Europe and Asia as ornamental plants. Their seeds ended up spreading in nature.

The biggest culprit? Amur honeysuckle, a woody shrub that has invaded many eastern forests.

“It escaped into the wild and is spreading on its own,” said Conover, a biology professor at UC’s College of Arts and Sciences.

Not to be confused with the native trumpet honeysuckle, which grows in southern states and is referenced in the works of American writers William Faulkner and Robert Frost, Amur honeysuckle is a shrub from Asia that has delicate white flowers. in the spring and red berries in the fall.

“The Amur honeysuckle is now the most abundant woody plant in Hamilton County,” he said. “A bush can produce thousands of seeds which are dispersed by birds and mammals.”

A survey by Braun in 1961 found that Amur honeysuckle was beginning to grow in parts of Hamilton County but was not yet spreading wild to other Ohio counties. Today, it is a dominant woody plant found throughout the state, virtually crowding out other low vegetation, according to the study.

“In some forests, the layer of Amur honeysuckle is so dense that the only remaining native species are older trees whose canopy is already growing above the shrub layer,” the study says.

“It leafs out earlier than native woody plants and retains its leaves longer in the fall,” Conover said.

Some invasive plants succeed because they produce chemicals that hinder the growth or germination of nearby competitors, an insidious weapon called allelopathy, he said.

Conover said where these introduced plants are, there is often much less biodiversity to support wildlife and the food chain. Once they take hold, eradicating plants like Amur honeysuckle takes a lot of work, money and time.

“Native plants just don’t stand a chance. Everything that depends on native plants — insects, birds — can be lost,” Conover said. “When they introduce non-native plants to the United States, they may also import fungal diseases that can wipe out native trees, which happened with the American chestnut.”

Calloused pear trees with their pretty spring flowers and quick growing time were a favorite tree to plant in the front yards of new subdivisions. Today they grow wild along highways and forests.

Ohio lawmakers plan to phase in a ban on the sale of Callery pear trees in 2023.

The UC survey found dozens of other examples of alien species that took root in the woods of southwestern Ohio, including chinaberry, tree of heaven, winged spindle , European buckthorn, oriental bittersweet, common privet and lesser periwinkle. He also found Norway maple, Amur cork and white poplar as well as herbaceous species such as lesser celandine, garlic mustard, Japanese knotweed and Japanese stilt.

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