State Hopes to Keep Invasive Plants in Check with Rule Additions

Indiana’s Terrestrial Plant Rule makes it illegal to sell, distribute or introduce to the state 44 species of plants designated as invasive pests.
April 26, 2019

The state of Indiana has implemented a rule that designates 44 species of plants as invasive pests.

The Terrestrial Plant Rule makes it illegal to introduce plant species on the list that are not already found in Indiana. The rule will also make it illegal to sell, gift, barter, exchange, distribute or introduce those plants in the state beginning April 18, 2020.

This is a screenshot of Indiana DNR's Terrestrial Plants Rule page.
The Terrestrial Plant Rule makes it illegal to introduce plant species on the list that are not already found in Indiana. The rule will also make it illegal to sell, gift, barter, exchange, distribute or introduce those plants in the state beginning April 18, 2020.

Every spring, plants in the state of Indiana begin their yearly renewal. Dormant tree limbs and bare patches of ground suddenly develop buds and vegetation, and the plant life for which the state is known returns.

From afar, Hoosiers see a harmony of green everywhere sunlight, water and crucial nutrients join to spark life. But up close, a silent battle is fought for territory.

The state’s native plants struggle to hold the lands they have held for years, as an invasion of plants introduced into the state begin their own fight for life.

“Invasive plants are plants that are not native or are exotic and have been introduced intentionally or accidentally,” said Will Drews, vice president of Southern Indiana Cooperative Invasives Management, a non-profit group dedicated to limiting the damage caused by invasive species throughout all of Indiana. “What happens is, they get established here and harm our health, the environment or the economy.”

Invasive plant species are spread by wildlife, waterways and through the air, and take over the habitats of native plants. The invasive plants do not provide the same resources as native plants and change the way an ecosystem works.

“The biggest problem about them is that they don’t stay put,” Drews said. “They’re moved by all these different mechanisms and they keep moving, so it’s tough to keep on top of them.”

The list includes 44 of the species rated as highly invasive and most detrimental to the state by the Invasive Plant Advisory Committee of the Indiana Invasive Species Council. The list includes commonly known species like garlic mustard, tree of heaven and a series of honeysuckle varieties.

This is a picture of garlic mustard.
The Terrestrial Plants Rule lists 44 plant species considered invasive in Indiana. The list includes the highly invasive garlic mustard.

Garlic mustard is originally from Europe and received a “Very High” invasiveness rank. Researchers found that the plant would cause major, possibly irreversible alteration or disruption of ecosystem processes, and had a high rate of reproduction and chance for long-distance dispersal. Garlic mustard is found in many areas across the state. Communities and groups often hold events to clear the plant from public areas.

The tree of heaven originated in China and received a “High” invasiveness rank. Researchers found the plant also caused major disruptions and alterations to native ecosystems in many parts of the state, but found that the tree of heaven had less of an impact on natural plant community structures and compositions.

Also included in the new rule are a series of common but highly invasive Asian bush honeysuckle variants like Amur, Tatarian, Morrow’s and Bell’s honeysuckles.

Drews hopes the new rule will help keep invasive plants in check and limit the damage people knowingly or unknowingly cause to the state’s native ecosystems.

“We cannot force people to control invasive plants, and therein lies some of the problem if people don’t know or care about the issue,” said Drews. “You can get into trouble in the fact that you know you have a park on one side that’s working really hard to control invasive plants, and they can have a neighbor who doesn’t care at all and is harboring a lot of plants. There’s that constant battle of all those plants moving on over to that other side and keeping on going.”

Although the Terrestrial Plant Rule bans a large majority of plants considered invasive in the state, some are worried that two major omissions may have serious repercussions.

The list omits two highly invasive trees popular for landscape adornment – the Norway maple and the Callery pear tree, also known as Bradford pear, ornamental pear and Cleveland select tree.

This is a picture of a Norway maple.
Norway maples, like this one found in Fort Harrison State Park, are highly invasive, but are not included in the Terrestrial Plants Rule. Courtesy - Butler University

The Norway maple is found mainly in central and northern Indiana. It’s been found to alter the functioning of temperate forest ecosystems in the state and had a stronger effect on soils than any of the dominant native trees species. The tree also cast heavier shade than native trees and changed native erosion levels.

According to the Indiana Department of Natural Resources, the Callery pear trees have been popular in landscaping tree for decades because of their white flowers, glossy green foliage and purple fall color. They have become so popular they are crowding out native Indiana trees.

“Just take a look for glossy leaved, egg-shaped trees in highway interchanges,” said Carrie Tauscher, DNR urban forestry coordinator. “It’s common to find them in unmown areas under utility lines and in lots and fields initially cleared for construction that are then left fallow.”

The trees are beautiful all year, but pose a serious risk to native plant life. Researchers found that the trees “negatively impacted Indiana state-listed or federal-listed plants or animals,” and displaced, killed or hybridized plants in at least 20% of the areas where the tree was found.

This is a picture of a Callery pear tree flower.
Callery trees and its offshoots are considered highly invasive but were not included in the Terrestrial Plants Rule. Courtesy - Purdue University

Last year, the Hoosier Chapter of the Sierra Club and several other conservation groups caused a political stir after opposing the planting of a Callery pear tree sapling in Fort Wayne. The sapling grew from a tree that survived the 9/11 terror attack in New York City and was sent to 16 Indiana communities.

Drews says the Callery pear and the Norway maple were left off the list because they would cause a significant economic impact to nurseries and big box retail stores that sell the two invasive trees. DNR also admits the reason for the omission.

“After reviewing all of the species that are included in the rule it was determined that Callery pear and Norway maple would have the largest economic impact to small businesses in Indiana if removed from trade,” said Megan Abraham, director of the DNR’s Division of Entomology and Plant Pathology, in an e-mail. “In order to get the rule through the process efficiently and in a timely manner it was decided to leave off those species and review them at a later date to be included in the rule.”

Indiana Environmental Reporter reached out to several nurseries and home improvement stores that currently sell some of the plants on the Terrestrial Plants Rule list. All said they would obey the law as it is written.

A representative from Home Depot, which sells invasive Callery trees as Cleveland select flowering pear trees, told the Indiana Environmental Reporter that the company is mindful of what plants are sold in a given region.

This is a screenshot of a Cleveland select tree sold on Home Depot's website.
Home Depot sells Callery pear trees as Cleveland Select, but says it will stop selling the tree if a state says it is invasive and harmful.

“If the state says that something is invasive and harmful, we will obviously stop selling it,” said Margaret Smith of Home Depot’s corporate communications. “We have live goods merchants who are very knowledgeable in what they do and they buy specifically for the regions of the country for which they’re responsible for. We look at our plant buying on the regional level.”

The company, though, did not mention whether it would stop selling the Cleveland select tree in Indiana or limit where the tree would be sold.

Because the plants were not included in the rule, it’s now up to individual Hoosiers to keep the legal invasive plants from taking over the state’s natural vegetation.

“You lose something when instead of seeing the forest or the native glade you’re used to, you see a jungle of invasive plant species just taking it over,” Drews said. “We gotta keep these species. We gotta keep these natural areas healthy, and I think that helps us with tourism and keeping to our Hoosier roots.”

People violating the Terrestrial Plant Rule could face a fine. You can report invasive plants to the DNR Division of Entomology & Plant Pathology.

State Hopes to Keep Invasive Plants in Check with Rule Additions