Why Invasive Plants Are Bad

Why Invasive Plants Are Bad

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

How to find out which plants are native

Talking with someone the other day, it came up that this would be a good topic for a blog post.  When you go to a nursery or garden center, how do you know which plants are native and which ones are invasive?  It’s actually pretty simple these days, lucky for us.  Most of us carry the “World Wide Web” with us at all times, so it’s easy to quickly find out where a species of plant comes from if the plants for sale are labelled.  You can just Google the species name and the word “native”!

google salvia greggii

There’s a USDA webpage that is helpful in learning where plants come from and where they are invasive.  The picture below shows what I got when I searched on their website for Lonicera sempervirens, a plant that is native to the eastern U.S., as shown by indicating in green the states in which the plant is native and in blue the areas where it has been introduced.  In the table to the left of the map, it in dictates that the species is native (N) to the U.S. but has been introduced (I) in Canada.


Below, I’ve searched for Ligustrum sinense, a plant that is not native to the U.S..  This plant has been introduced to many states in the east and southern U.S., as seen by the blue on the map and the “I” indicated next to the native status in the table to the left of the map.  (There is a legend for the map just below it on the webpage to indicate what the colors indicate.)


Below, you can see that I have Googled “Nandina invasive”.  It is pretty clear from the first few hits that Nandina has invasive tendencies.  If it is invasive anywhere in the U.S., you can expect that it will likely become invasive here too.  I’ll post another blog soon to explain the reasons why it’s so important to avoid planting invasive species.


For some plant labels, it’s a bit difficult for a less experienced botanist or gardener to determincultivar tage what the name to google is.  Take the tag at the left, for example.  On the front of this tag, it simply says ‘Miss Molly’.  (Many times, there will be more specific name information on the back of the plant tag in tiny writing.)  Simply googling “‘Miss Molly'” isn’t very helpful, but if I google “‘Miss Molly’ pink plant”, I immediately find what I’m looking for and see that it’s a species of Buddleia, a butterfly bush.  Then I can google “Buddleia native” to find out if it’s native to my area.  It’s not.  It’s actually becoming invasive in many places.  😦

I hope this blog was a bit helpful.  If you have any questions, I’d be happy to answer them for you.





Witch hazel has a lot of gall!


Walking around the yard the other day, I noticed these little bumps all over the leaves of my witch hazel tree which, otherwise, looks quite happy and healthy.  Some of the bumps are green, others are red.


These galls are caused by the witch hazel gall aphid, Hormaphis hamamelidis.  The growth on the leaf is a response of the plant to an injection of salivary secretions, and possibly an infecting virus, by the aphid.  The aphid’s offspring then develop inside the gall where they are protected from predators as they develop, getting the nutrients they need from the sap of the plant.

gall aphids cropped

This species of aphid feeds on witch hazel and birch trees.  This paper is a very thorough study of the witch hazel gall aphids:

Lewis, I.F. and L. Walton.  1958.  Gall-formation on Hamamelis virginiana resulting from material injected by the aphid Hormaphis hamamelidis.  Transactions of the American Microscopical Society  77(2): 146-200.

March for Science

Today was Earth Day.  On President Trump’s inauguration day in January, some scientists initiated the idea that there should be a “March for Science” organized to show the support of Americans for science and evidence-based decision-making.  The scientists involved in the initial planning of this decided Earth Day would be a good day to do this.  So today, all around the world, people marched to show their support for science.  I participated in the march here in Charlotte.  It was very inspiring to see so many people, hopeful for the future and supporting scientific endeavors of all sorts.

I helped with the educational booth for the local chapter of the NC Native Plant society.  We handed out lists of pollinator-friendly plants, taught people about invasive plants they may have in their yard, and enlightened some people about the diversity of pollinators that exists.  I have never seen so many people eager for knowledge and excited to learn about new things.  It was a great day for Earth!

Mosquito control

I got an email today from a former student asking me about potential impacts of mosquito control spraying programs on pollinators.  The most important thing to realize is that there are currently no mosquito-specific pesticides on the market.  That means that any pesticide that will kill mosquitoes will certainly kill many other types of organisms with which it comes into contact.

Many webpages and advertisements for mosquito control companies (I guess I shouldn’t name names) say that they try to minimize impact on pollinators by avoiding spraying bee hives.  OK, that’s a start.  But what about bees that don’t live in hives?  Very few types of bees live in hives.  Many of them simply live in a hole in the ground or a hole in a branch.

Some sprayers claim that they direct their spray at the ground instead of in the air specifically so they will minimize effects to other pollinators. But, again, many bees live in holes in the ground, as do many other pollinators such as ants and beetles, and many caterpillars (which are, of course, larval butterflies and moths) spend the night nestled in ground vegetation and leaf litter.  So spraying the pesticide on the ground is not minimizing impact on pollinating insects.

One company’s website stated that they use a type of pesticide called sumithrin that is not toxic to bees.  It is disturbing that this company claims sumithrin is not toxic to bees considering the National Pesticide Information Center states it is toxic to insects via contact or ingestion, affecting their nervous system by keeping open the sodium channels for prolonged periods of time.  This chemical is a type of pyrethroid, some kinds of which are produced by plants like chrysanthemums.  Some pyrethroid chemicals are referred to as organic because they are produced by plants, naturally.  Just because a chemical is produced by plants doesn’t mean it can’t be toxic.

One technique advertised by mosquito sprayers to minimize impact on pollinators is to spray in the early evening, when the pesticide will have all night to break down before most pollinators are active.  Unfortunately, some of the chemicals likely to be used by these companies only break down when exposed to sunlight, so they will not break down overnight.

Overall, the best way to control mosquito populations is to limit their reproduction.  Mosquitoes lay eggs and the larvae develop in standing water.  They don’t need much water– a couple of tablespoons’ worth will do.  Monitor your property so that there is no standing water.  After a rain, make sure there are no cups, bowls, cans, pots, or buckets holding water.  A common place to find standing water is in the bottom of pots designed to hold a water reservoir for the plants.  Tip the pots to the side and let all the excess water drain out.

Adult mosquitoes love to hide in dense vegetation, where it’s nice and humid!  Dense ground covers like English ivy and monkey grass (Liriope spp.) harbor large populations of mosquitoes, as do dense shrubs like heavily pruned holly bushes.  Get rid of such vegetation and you’ll notice a significant decline in the mosquito populations in your yard!

Another good way to get rid of mosquitoes in your yard is to encourage mosquito predators!  Many mosquitoes are active at night, and bats are prolific feeders on them.  But one of the most bothersome mosquitoes here in the Charlotte area is the Asian tiger mosquito, and these evil little buggers are active all day.  Landscape your yard such that you are encouraging wildlife such as birds and lizards to hang out and forage in your yard and you will have your own resident posse of mosquito controllers!

Happy surprises!

Happy surprises!

I began introducing native plants into the yard when we moved here 10 years ago.  Over the past decade, I have planted a lot of things that didn’t make it.  To be frank, I am a HORRIBLE caretaker of plants.  The plants that make it in my yard truly must be the best suited for their environment.  I water new plants daily for a couple of weeks and then a few times a week for another couple of weeks and then they are pretty much on their own.  They get no TLC from me.

I don’t ever pull out dead things and throw them away.   Every now and then, someone surprises me by making a comeback!  There have been a few times that a Phlox seems to have just disappeared and then, a few years later, wow!  Huh!  That must be the Phlox I had planted there years ago and forgot about!

I have tried a few times to introduce partridgeberry (Mitchella repens) into my yard in a few different places.  It’s such a cute little plant and seems to do so well in the dry, shady woods where I see it when I’m hiking. It seems like it would do well in my own dry, shady yard.  But it has never “taken”.  Just this week, however, I have noticed it in two of the places where I know I tried to plant it several years ago.  I guess it’s just been hanging out dormant all this time.  This summer, we did get rain much more frequently than we usually do in the summer. Maybe the frequent rains gave it what I never have– enough water to finally get growing.  I hope it sticks around.

Another happy surprise this week took place in the newly establishing pollinator meadow.  This is an area adjacent to our property that, until last summer, had been pretty much just a vacant lot.  Last summer, we had the opportunity to purchase the lot, so we did.  I’ve spent the last year establishing a pollinator meadow in the front quarter of it, where there is enough open area for some sun-loving plants, and introducing native shrubs, ferns, and understory trees under the 50+ year-old trees in the back portion.

In the sunny area, there have been lots of typical annual “weedy” grasses like crabgrass, a few random dicots have sprouted up here and there on their own– clover, violets, columbine…  And then there’s this one kind of plant that sprouted up all over the place.  At first, I thought it was ragweed due to the highly divided leaves, but the edges are strongly serrated.  I figured I’d just let it grow until it flowered so I could see what it is.  There are dozens, probably more than a hundred, of these plants out there and some of them have gotten to be four feet tall and almost as wide.  I’ve waited and waited for them to do something so I could identify them.  Finally, this week, a few of them have burst into bloom.  It’s a Bidens, I’m pretty sure– the flowers look very similar to those of brown- or black-eyed Susans.  And they are all covered with flower buds!  Within the next couple of weeks, the pollinator meadow is going to look just like a sea of little sunflowers!  How absolutely fun that is!!!  🙂

(The picture featured at the top of this blog was later added to show the Bidens in bloom.)


How it all began…

Our yard, the back, especially, is very wooded but other than that, when we bought our house in 2006, the yard was pretty typical.  The front was mostly lawn, except for one corner where one of those big box-like storage unit thingies had been sitting for who knows how long– the ground was completely bare there.  There were lots of hostas and numerous azaleas, gardenias, and camellias that have been here probably since the house was built in the middle of the last century.  And, of course, there were Chinese privet, Japanese privet, “sacred” bamboo and running bamboo, English ivy, and other invasive banes of my existence.

I spent the first few years trying to “reclaim” the front yard from lawn and trying to encourage the bare area to recover. I put an ad on Craig’s List for people to come dig up hostas if they wanted them.  About a dozen people showed up, one couple with an RV.  They all left with as many hostas as they could fit in their cars (or RV).  And my yard has been hosta-free since!  The struggles against the other shade-loving non-natives have not been as simple.  To this day, I still have not managed to get rid of the forest of bamboo and English ivy covering the back quarter of the yard.

I put lots of native shrubs in the front yard such that only about a quarter of it remained “lawn”.  I refuse to cut the grass weekly, and can’t see that it ever needed that, really.  I’m sure the neighbors thought I was nuts– instead of dragging out the lawn mower, I walk(ed) around the front yard with hedge trimmers cutting off the flowering heads of the grasses– the only parts of the grass that ever get taller than the 12″ stated in the city neighborhood regulations.  I also started putting flags in the yard to mark tree seedlings that I wanted to let grow– dogwoods and redbuds, mostly– so I would be extra careful with the hedge trimmers in those areas.

One summer, when I had a lot of flags out to mark seedlings and had a broken arm that prevented me from using the hedge trimmers for a couple of months, I got a letter from the city saying my yard was not up to code.  Apparently, a neighbor had thought that I was using all the flags to mark fire ant nests and had complained about that!  The neighbor had obviously not bothered to actually look for ant nests; there were none to be seen.  But that brings me to a little bit of science you may be interested in–

Fire ants are poor competitors with other, native ants.  Fire ants can usually only move into an area when there are no other ants around.  So it’s a bad idea to assume all ant hills are fire ants.  It is, instead, a GOOD idea to keep the native ants around so you can keep the fire ants out! Here’s what I do– I find a stick a few feet long and stand just within the stick’s reach of the ant mound.  I poke at the ant mound a few times.  If ants come pouring out all over the place, they’re fire ants.  If only a few ants come wandering out to see what the fuss is, they’re not fire ants.  Only once in more than 10 years have we had fire ants.  That was in the driveway next door when the whole yard had been razed, but that’s another story.

One of the types of native shrubs that I had planted in our front yard was Hypericum frondosum, one of the species of St. John’s wort.  These were gorgeous little shrubs with bright yellow flowers and bluish-green leaves that turned a bit reddish in the winter but hung on.  A few years ago, they all shriveled up when we got a super harsh cold front and they never recovered.  I miss those shrubs.  And the front yard hasn’t looked as good since.  I’ve been distracted with other projects since then and have not gotten around to putting anything else there.  Just within the past couple of weeks, I’ve noticed two little sprigs of Hypericum poking up where the shrubs used to be.  Dare I hope they’ll come back?  Should I wait for them?  Probably not…  That area needs to be spruced up sooner than that would take, I think.