By: Dr. Sigrid Resh, Coordinator, Keweenaw Invasive Species Management Area, and Research Assistant Professor, Michigan Technological University (scresh@mtu.edu); Lauren Fliearman, Applied Ecology and Environmental Science undergraduate, Michigan Technological University (lcfliear@mtu.edu); Erin Mauk, Wildlife Ecology and Conservation, Michigan Technological University (ermauk@mtu.edu).

We at KISMA often get asked why we care about invasive species being spread around our natural areas? Or, what is wrong with planting invasive species in their yards? Isn’t one green plant as good as another? So, we are going to try to answer those questions.

First we’ll start with a standard definition of invasive species, which is a species that is not native to the area in question and that may cause harm to the ecosystem, the economy, or the health of humans in that area. We are going to focus on plants, because that is what the Keweenaw Invasive Species Management Area mostly focuses on. Not all non-native plants become invasive, but, when a non-native plant spreads in an area at the expense of the native plants and wildlife, it causes problems.

Why do some non-native species become invasive? Invasive species are not on a level playing field with the native species, which have evolved to be in an area over thousands of years. Invasive species, because they were moved to a new part of the world, do not have predators, competitors, or diseases that keep them in check or, in other words, keep them from dominating in an ecosystem. This means that native species lose space and resources to invasive species because invasive species have an unfair competitive advantage. This may sound like they are then better suited to this environment, but in fact they are harming our ecosystems.

An ecosystem, or nature in general, does not consist of a bunch of species living independently from each other, just like you are not living independently from your community. You require farmers to provide much of your food, power companies for energy, doctors for health care, and friends and family to make it all worthwhile, not to mention a place to live that is reasonably close to all of those things. Each individual in an ecosystem from a fungus on a tree root to a frog in a vernal pool to a migrating bird, relies on the other parts of its community to provide food and habitat for it to survive and reproduce.

So what do native species do better than invasive species? They provide habitat for other native species; native animals use native plants, which feed other native animals in a complex food web. Research in Pennsylvania conducted by Karin Burghardt and others published in Biological Conservation (2009) showed that “bird species of regional conservation concern were 8 times more abundant and significantly more diverse” on properties with more native plant cover relative to non-native plant cover (https://doi.org/10.1111/j.1523-1739.2008.01076.x). Similarly, in 2017, research in Washington D.C. published in Biological Conservation and conducted by Desiree Narango and others showed that yards with native plants used for landscaping had higher native caterpillar populations and more breeding chickadees compared with yards that had more non-native plants (https://doi.org/10.1016/j.biocon.2017.06.029). Because invasive species don’t tend to get eaten as much, they don’t pass along their energy to other organisms in the food web.

Now what happens if an invasive species is introduced to an ecosystem and dominates? There would be less native species. The other native ecosystem inhabitants can’t find as much food or shelter. Like if we humans couldn’t get food to grow here or be delivered, or all doctors left, or our loved ones all moved away. The things that made this a useful home to native inhabitants were taken away. Some of you may recognize that we have been talking about biodiversity. As explained by Dr. Douglas W. Tallamy in “Bringing Nature Home” in 2007, biodiversity means there are many species performing similar tasks in an ecosystem. This means there is back-up support for ecosystems to continue to thrive despite common disturbances like fire, timber harvest, pests and disease, and other climate-driven events such as early and late frosts, wind, drought, and so on.

The back-up species inherent in biodiversity allow an ecosystem to recover from disturbances even when some species are more strongly impacted than others. However, invasive species can undermine this balance.

Through their research, G. Mollot, J.H Pantel, and T.N Romanuk (2017) were able to confirm that invasive species impact biodiversity by decreasing species richness, a component of biodiversity (https://doi.org/10.1016/bs.aecr.2016.10.002). Specifically, the researchers found that a majority of the decline is happening in temperate forests like ours.

So, to recap, invasive species have an unfair advantage when introduced to a new habitat allowing spread at the expense of native species, causing direct and indirect loss of native species. From a completely human-focused perspective, this means that we humans will also have problems getting what we need to live, which are called ecosystem services like clean air, clean water, food, lumber for housing and fiber for clothes. It is the diversity in our ecosystems that maintains their capacity to continue to deliver what humans and other animals need to thrive and survive on this planet.

Simple actions such as purchasing and planting natives in the local area can combat the spread of invasives while restoring the lost biodiversity. If you would like to learn more about invasive species or how biodiversity is crucial for healthy ecosystems, check out KISMA’s website https://www.mtu.edu/kisma/ as well as read “Nature’s Best Hope” by Dougles W. Tallamy from 2020 for more information. Contact kisma.up@gmail.com for a list of regional native species. For purchasing native species, check out Designs by Nature 906-250-9157 – Marquette (https://www.upnativeplants.com/) and the plant sales at our regional Conservation Districts: Houghton Keweenaw (https://www.hkconserve.com); Iron Baraga (https://ironbaragacd.org); Marquette (http://www.marquettecd.com).