Investigating Invasive Species — A Basic Review

Author: Lisa Trapp

The conversation about invasive species isn’t new. In fact, it seems like every day we turn around and hear about a new invasive plant, insect, reptile, or even bacteria. According to the USGS Invasive Species Program there are more than 6,500 invasive species established in the United States. Though this number can feel really daunting, it’s important to remember that understanding invasive species, how they function, and how to best handle their removal, can make a difference not only locally but on the global scale as well. And while a lasting impact takes a concerted effort community wide, educating yourself on the invasive species taking hold locally and getting involved in fighting back against them is a worthwhile first step.

Invasive English Ivy girdling and killing native trees at a local Richmond Park (2019).

An invasive species is defined as an organism that is not historically found in a particular area and causes economic or environmental harm. Environmental harm can be directly related to humans, animals and/or plants but put simply, invasive species damage the way an entire ecosystem functions. With so many identifiable species worldwide, we can find invasives almost anywhere we look from Autumn Olive (Elaeagnus umbellata) to Zebra Mussels (Dreissena polymorpha). Unfortunately, the National Wildlife Federation estimates that roughly 42% of threatened or endangered species are at risk due to invasive species.

Keep in mind, when thinking about plants, invasive species differ from a naturalized, ornamental, or generally “exotic” species. In addition, some of our native species, given the right conditions, can be harmful in their own right. We call these opportunistic natives, as they can exhibit similar invasive behaviors, like outcompeting other native plants, creating monocultures, and lowering biodiversity.

It’s impossible to cover the ins and outs of 6500 invasive species in one blog post, so we’re narrowing our focus to invasive plants. Even more specifically, the Virginia Department of Conservation and Recreation’s Division of Natural Heritage has identified 90 plant species that pose invasive threats to our parks. But what is it that makes these plants so likely to take over? Invasive plants often exhibit similar developmental characteristics. Typically, they have rapid growth, and can often stay evergreen or grow at a time when our native plants are dormant. They produce a large number of seeds, and utilize advanced seed dispersal techniques. Some invasive plants can even produce toxins that prevent other plants from growing nearby. But the icing on the cake is that they lack natural predators to keep their growth in check. Our native herbivores aren’t going to feed on a plant they don’t know, which allows these species to grow unfettered.

Invasive species removal is a costly process, but we can’t just leave “nature be”. Humans had a direct role, intentionally and accidentally, in the spread of species around the world and we may lose a number of plants and animals to extinction before nature recalibrates and finds balance on its own. Beyond species loss, there are also ecosystem function changes that can occur. Cogon grass (Imperata cylindrica), for example, which came to the U.S. in packing material from Asia, is one of the top 10 worst invasive species in the world. Not only does it not have nutritional value for wildlife, but it burns hotter and faster than our native grasses which can make wildfires spread more rapidly and cause more damage. Unfortunately, given their aggressive nature, many invasive plant species require multiple methods and years of targeted management in order to start decreasing their spread. But don’t let this deter you, dedicated invasive plant management teams and volunteers are constantly working toward habitat restoration, and success is possible!

Cross Creek Nursery Staff volunteered their time last week to manually remove invasive vines along the Kanawha Canal as part of an effort to reclaim that land back for native plants.

JRPS Invasive Plant Task Force organized volunteers to help with invasive plant removal on Chapel Island During RVA Arbor Week.

So, what can really be done? We talked a bit earlier this month about the invasive weeds we tackle on a regular basis in the garden beds but this winter we are also focused on trying to remove invasive species along the canal. At home, the best first step for managing invasive species in your yard is educating yourself on how to identify invasive plants. It is important when tackling removal that you know exactly what you are dealing with. Though not found in the Richmond area yet, invasive giant hogweed (Heracleum mantegazzianum) looks like something out of a Dr. Seuss book, resembling a very large queen anne’s lace. Removal of the plant should be done with extreme care, however, as contact with its sap can cause intense burns, permanent scarring, and photosensitivity. Some invasives will only start to die back if they are removed completely, or at a specific time of year. Tree of Heaven, from our example, will send out suckers if the tree is just cut back without an immediate herbicide treatment. Small herbaceous plants and vines should be double bagged and disposed of at a certified landfill and remember to replant any bare areas quickly, ideally with native species, to prevent invasives from moving back in.

If you want help getting started with identifying what plant species you should be looking out for, consider joining us for a community work day, or signing up to volunteer with the James River Park System’s Invasive Plant Task Force. You’ll learn valuable information that you can take home and apply in your own lawn and garden!

For more information on invasive species management check out some of these resources:

Websites:
- DCR – Virginia Invasive PLant Species List – https://www.dcr.virginia.gov/natural-heritage/invsppdflist
- USGS Invasive Species Program – https://www.usgs.gov/programs/invasive-species-program
- The National Wildlife Federation – https://www.nwf.org/Educational-Resources/Wildlife-Guide/Threats-to-Wildlife/Invasive-Species
Books:
- Plant Invaders of the Mid-Atlantic
Local Organizations:
- JRPS IPTF Task Force web link – https://jamesriverpark.org/james-river-park-system-invasive-plant-task-force/
  - Richmond Invasive Species Awareness week