Invasive Plants: Assassins of the Woodlands

Did you know there are 126 invasive species of plants in Indiana? While it seems like a small number out of the 2,000 or so plant types that grow in the Hoosier state, they can quickly cause significant damage to local ecosystems if not managed.

Today, we’re talking about why invasive plant species are so detrimental to native plants, several common ones that can be found in central Indiana, and what you can do to help prevent the spread of these invasive species.

Why Are Invasive Plants So Detrimental?

First of all, invasive plants are not synonymous with non-native. In fact, plenty of non-native species cause no ecological problems. In a nutshell, what classifies a plant as invasive is when they are hardy, fast-spreading, and grow quickly, so much so that they take over a habitat. Many invasive species get a head start in the spring, opening their leaves earlier than native plants, essentially stealing water, sunlight, and space from surrounding native species. They also tend to produce a lot of seeds. Invasive plants also get out of control when native wildlife don’t use them as a food source. These plants are also difficult to kill and find numerous ways to spread and regrow.

Though they may originate in a confined urban yard, their seeds are easily transmissible to woodland areas by birds, wind, or even our clothing and shoes. When native plants die off and invasive species take over, it changes what food is available to wildlife. So, it’s not just about indigenous species being killed off. It’s a matter of animal populations dwindling due to a loss of food sources as well.

Larger invasive plant species, such as the Callery pear (commonly known as the Bradford pear) can even cause property damage, putting a dollar amount on the type of havoc invasive plants and trees are capable of. Although they have beautiful white blossoms in the spring, they are structurally very weak trees. In fact, it was stated in an Indy Star article that “much of the damage street departments in Hamilton County deal with is broken Callery pears.”

Speaking of money, the costs of trying to control the population of invasive species add up as well, from the man-power efforts to remove them to trying to pass legislation to ban their sale.

Luckily, some of these plants have already been banned from sale. Just last spring, 44 species of invasive plants were banned from being sold, gifted, exchanged, and even transported within the state. This was thanks to the new Terrestrial Plant Rule being passed.

Obviously, the hardest hit by this rule were many nursery and landscaping companies and their consumers/clients; however, this will hopefully help them become more enlightened about use native plants in place of invasive plants and better educate the public about their benefits in traditional landscaping.

Common Invasives of Central Indiana

Honeysuckle – Did you know there are several species of honeysuckle that are invasive in Indiana? While the sweet nectar may have been fun to eat as a kid, honeysuckle causes big problems. It grows rapidly and earlier than other plants in the spring. Before long, it completely takes over neighboring plants, vining on top of and covering them until they’re completed deprived of sunlight and root space.

Tree of Heaven – While fewer trees make the invasive list than smaller plants, ailanthus altissima, or Tree of Heaven, is one exception. It is a quick-growing tree and can form dense clonal thickets, suffocating other native trees. Elimination is difficult and if the roots aren’t taken out as well, new shoots will pop up from them even if herbicides have been used. It doesn’t mind urban areas and has thrived in less-than-ideal conditions such as mine spoils and industrial wastelands.

Purple Loosestrife – While this perennial produces beautiful purple flowers from mid to late summer, it’s also detrimental to wetlands. This plant favors marshes, ditches, and anywhere that sees a fair amount of water. The problem is that most animals and insects do not use it for food or shelter. With its already aggressive growing behavior, it doesn’t take long for it to crowd out native plants and clog waterways.

Autumn Olive – These shrubs are easily identifiable by their small berries, which are about the size of a pea, that turn pinkish-red in late summer. While birds love them as a food source and even nesting site, they also help in the plant’s dispersal. Autumn olives can produce a whopping 80 pounds of fruit in one season, so it’s easy to see how they become belligerent in an area. They can also affect the soil acidity negatively and cause further harm to native plants.

Japanese Knotweed – This herbaceous perennial grows surprisingly fast and doesn’t mind disturbed areas. It is even known to cause problems with structures, finding cracks in foundations and furthering problems. Japanese Knotweed can grow up to 10cm per day. That’s almost 4 inches! Even though they don’t use seeds as their main means of dispersal, it’s easy to see how this invasive plant can quickly take over an area due to its rapid growth.

Winter Creeper – Winter creeper looks similar to Japanese honeysuckle and grows just as aggressively. Though it typically starts as a groundcover, it can also vine out and climb up the trunks of trees. It takes advantage of forest margins and openings, especially those caused by insects, fire, and wind. Like autumn olives, their dispersal is also helped by birds. Aside from taking over other plants due to their quick growth, winter creeper also leaches nutrients from the soil.

Canadian Thistle – Though similar in appearance to native thistle species, this version easily crowds them out. It tends to grow in open areas such as fields and meadows. Using shoots, it grows prolifically and quickly out-competes native grasses and plants. This can be especially detrimental in pastures where livestock graze as they avoid the prickly plants.

Garlic mustard, winged burning bush, Callery pears, and English ivy are just a few other invasive species found throughout central Indiana. For a comprehensive list, check out this page on invasive exotic plants from Purdue University.

How You Can Help

Invasive removal is something anyone can help with. Here are a few simple ways you can get involved.

• Learn more about native plant species that could be in your area. After properly identifying any, learn the best way to remove them from your property.
• Join your local CISMA (Cooperative Invasive Species Management Area). These groups generally work in county-wide areas, working together with interested parties and local agencies to eradicate invasive species specific to local habitats. Most meet regularly, host “weed wrangles,” and promote passing legislative policies, such as the Terrestrial Plant Rule.
• Invasive plant pulls are also held regularly at state parks around Indiana. These are mostly in the spring and fall, so be sure to check the DNR calendar
• Be sure your shoes and clothes are free from seeds, burrs, and such when leaving a wilderness area so you don’t inadvertently bring an invasive plant to your own backyard!
• Use native plants in your landscaping. This list of native plants and where they grow best is a good starting point for ideas.
• Hire a company (like us) to help you get your property under control and back full of thriving native plant species.

Greenscape Geeks is a central Indiana landscape architecture and landscape design, construction, and lawn maintenance company, serving Indianapolis (including Meridian Kessler, Herron Morton, Williams Creek, and Irvington), Carmel, Noblesville, Fishers, and Zionsville.

This is a guest post by Alicia Owen