Ecologists, field biologists, and conservationists have strongly negative feelings towards “invasive” plants. This article explains why they are so much of a problem. First, let’s clarify a bit of terminology. What is an invasive plant? An invasive plant is one that is not native to an area and that is having a negative impact on native habitats. What does it mean for a plant to be “not native” to an area? Any species that has not been in an area for thousands of years such that it has evolved with its cohabitant species is not native to that area. The terms “non-native” and “exotic” may be used interchangeably with regard to species nativity.
One important thing to understand is that not all non-native plants are invasive. Thinking of non-native plants, you may consider plants such as the tomato, the apple, Italian oregano, autumn olive, Chinese privet… We have literally hundreds of non-native plants. But it’s only the ones that are invasive that are cause for concern. Tomatoes, apples, and oregano tend to stay where you put them—they are not invasive. Autumn olive and Chinese privet are invasive. A person may say, “well, my autumn olive and Chinese privet plants are staying exactly where I put them in my yard. They’re not going anywhere!” But let’s take a wider look at the situation.
There are many wonderful forest preserves here in the Charlotte area. When you take a walk through McDowell or Reedy Creek or RibbonWalk Nature Preserve, one never sees a rogue tomato plant or apple tree growing in the woods. But we do see many autumn olive and Chinese privet bushes. This is why the autumn olive and Chinese privet (along with many others) are considered invasive. Birds eat the berries of the olive and privet shrubs that are planted in people’s yards and they end up pooping the seeds out in natural areas. The seeds sprout and grow into mature shrubs in the woods, where they produce more berries to be eaten by birds which then carry more seeds into more areas. This does not happen with tomatoes and apples. The birds may eat them, and they may poop out the seeds in a natural area, but the tomato and apple plants are not able to persist unaided in the natural areas.
What’s the problem with the autumn olive and Chinese privet being in the natural areas? Many people have been studying the ways that non-native species influence the areas they invade and the effects are actually quite complex. (My mom has advised me to keep my blogs short-and-sweet so I’m going to try to keep it simple and straight-forward for now and can then elaborate more on each of these in future posts.)
Some ways that non-native species affect the habitats they invade include:
1) They do not contribute much to the food chain. Birds may eat the fruits and butterflies may eat the nectar, but the primary food that most plants contribute to the food chain is their leaves. Most native leaf-eaters cannot digest the leaves of non-native plants, and frequently do not even recognize them as food. This basically results in the collapse of the food web.
2) They compete with the native plants for nutrients, light, space, and water. Many of the invasive plants in our area are evergreen, and many others leaf-out earlier in the spring than native plants do and retain their leaves later into the fall than native plants do; this longer leaf retention gives the non-native plants a competitive advantage over native plants. Fewer resources are available for the native plants, resulting in less food available for the animals.
3) They alter the soil chemistry in many ways. Their roots exude chemicals that alter the pH of the soil. This reduces the ability of native plants to extract nutrients from the soil. It also influences the types of organisms that can live in the soil and the rate at which things decompose. These, in turn, alter the food web.
In the Charlotte area, my students and I have found a paucity of earthworms and other soil-dwelling organisms in the soil around invasive plants compared to nearby areas without invasive plants. We have also found that the leaves of the invasive autumn olive decay much faster than those of our native beech tree.
Let’s return now to thinking about our local nature preserves. Vast areas of these woods are infested with invasive, non-native plants that contribute very little to the food web, yet take up substantial amounts of space, light, water, and nutrients. If we truly want to preserve natural areas, we need to do our best to stop the spread of invasive plants so the wildlife will have the food they need to survive. The base of the food chain is native plants. The invasive plants might as well be plastic, as far as their contribution to the food web is concerned.
This is a general overview, but I’d be happy to get into greater detail. Let me know your thoughts and questions!
Not sure what plants are considered invasive? Here’s a great resource where you can find out! https://www.invasiveplantatlas.org/index.html
Overwhelmed by the long lists of invasive species and just want to know if one certain species is invasive? See the previous post, titled “How to find out which plants are native”. It also explains how to find out which plants are invasive.
Need help figuring out which plants in your yard are invasive? As as ecological consultant, I can visit your yard and identify all your invasive plants. I can teach you how to recognize them and how to get rid of them. I can also help you select the most appropriate native plants with which to replace them!
#preservingnature #invasiveplants #nativeplants #protectingwildlife