Why Do We Have So Many Invasive Plants?

 

The topic of invasive plants is inextricably intertwined with the support for native plants because native plants and their habitats are the most at risk when exotic plants spread. 

Invasive plants are defined as exotic plants that have the ability spread on their own to the point that their spread disrupts native ecosystems. 

Not all exotic plants are invasive; in fact, most of them aren't. My husband helped me put together this overview of terminology.

Know your terms

Exotic plants arrive here initially in one of two ways: someone brought them on purpose (and that’s absolutely true for many of our worst ones) or they arrived accidentally (perhaps as part of cargo such as packing material or stray seeds that hitchhiked). Once they are here, rarely are they identified to be invasive, that determination comes later, even many years later.

Once they arrive, they may live quietly for many years, including being cultivated and passed along. Japanese honeysuckle (Lonicera japonica) was brought here as an ornamental but it is said that it took 80 years before it became apparent that it was spreading enough to be considered invasive. In the last 20 years, many of us watched as ornamental pears such as ‘Bradford’ (Pyrus calleryana) started to spread into natural areas. It is finally designated now as an invasive plant. 

Tree of Heaven

Two more recent pests are Autumn fern (Dryopteris erythrosora) - spreading into streams and natural areas - and Japanese chaff flower (Achyranthes japonica), a pest notably in the Atlanta area but spreading outward.

If invasive plants are so bad, you might wonder why we aren’t doing more about them. How do they spread? 

I like to describe it as the 3 W’s: wind, water, and wildlife. Once the seeds or root fragments arrive in a new spot, it is largely the twin forces of neglect and ignorance that allow them to thrive. Neglect and ignorance are solvable!

I remember being a kid in the 1970’s when the litter campaign was in full force. Litter bags for your car were all the rage – they were created to encourage people NOT to throw their trash out the window. Can you imagine that people thought that was ok? How times have changed.

We need a campaign to say that invasive plants are not ok. It’s not ok to have them and it’s not ok to just let them fill up the roadsides like so much trash. Cities and counties should take responsibility for their roads, learn to recognize these plants (easy with a smartphone or tablet), and have crews remove them just like they remove trash (litter pickup). 

Utility contractors that manage vegetation should be instructed not to just prune invasive trees to protect the lines, they should be instructed to cut them to the ground!

Developers should be required to identify and remove invasive plants on property being developed. Developments near me are leaving invasive plants on property edges, only removing them if they are physically in the way of some section they want to develop.

City, county, and state parks should include in their maintenance plans the detection and removal of invasive plants just like they detect and remove trash. I wrote recently about a park stream restoration project; invasive plants were removed but you could see where they still exist in the unrestored areas.

I hope one day that we look at managing invasive plants the same way we looked at trash in the 1970’s. Humans made this mess and it’s up to us to deal with it in a responsible way.

Landscape Spotlight: Virginia sweetspire (Itea virginica)

 

This month is bloom time for Virginia sweetspire (Itea virginica), a deciduous native shrub that naturally grows in moist areas. I always enjoy finding it in a natural areas and along streambanks where its modest green foliage allows it to hide in plain sight. It is native throughout Georgia and Florida (Hmm, I should get some for my daughter’s yard in the Florida panhandle).

Itea virginica

What has surprised me recently is the explosion of usage in designed landscapes near where I live in metro Atlanta. Driving around this past week – while it was blooming – made me realize how it can be and is being used in landscaping.

Virginia sweetspire can be a suckering shrub, a trait which is very beneficial in its natural habitat along streambanks. I am used to seeing it in stream restoration projects such as the one I profiled last week. It doesn’t always sucker – perhaps it is a response to damage or browsing – in fact, a group of 3 at the front of a neighborhood planted at least 5 years ago is still just that group of three.

It is usually described as a part-sun plant but I am seeing it used in full sun, even afternoon sun. These plants may have help in dealing with the extra sun by artificial irrigation (something to consider if you’re planning to use it in those conditions). It can have really nice fall color in addition to these spring blooms. Deer do browse on it some, so get some deer spray if that's an issue for you.

Here are some examples of landscape usage that I've seen over the years (and I've seen more but I just haven't photographed them). In the summer, the foliage is not particularly remarkable but it is handsome and can be dense enough for nesting birds. Fall color can be really nice on Virginia sweetspire and some cultivar names like 'Merlot' and 'Henry's Garnet' are indicators of that.

Consider this shrub for one of your landscape projects. It is usually available at larger nurseries and dwarf forms and reliable fall color cultivars are available. The cultivars have not impacted the pollinator benefits of the plant.

Stream Buffer Restoration

 

In regards to the support for native plant preservation and usage, I have long been disappointed in most city/county parks. What they consider “greenspace” is mostly ballfields, tennis courts, and playgrounds. Any natural areas and streams that might be in them are often ignored, degraded, and covered in invasive plants. But there are some streams that are important and attention to the buffers that protect them are required.

Signage

The end of restored section

At Wills Park in Alpharetta near me, I recently came across a buffer restoration project. While it seems the work is recent, I found this description of the project dating back to 2018: “Foe Killer Creek is a perennial stream that flows through Wills Park in Alpharetta, continues into Big Creek and eventually into the Chattahoochee River. Unfortunately, the creek has been identified as an impaired (polluted) stream due to increased presence of fecal coliform bacteria and sediment load.”

Sediment-filled area not yet restored

Restored area with willow

Only part of the stream has been restored so far and hopefully other sections will be addressed as well in the future. The plants installed include trees (oaks, blackgum, sweetbay magnolia, hollies, black willow); shrubs (Virginia sweetspire, dwarf wax myrtle); and perennials (ferns, lizard’s tail, river oats).

Lizard's tail, Virginia sweetspire, river oats, wax myrtle

The stream in the restored area looked pretty clear and small fish and water strider bugs were visible from a pedestrian bridge and I saw a frog hop in. Signs and orange mesh fence help to inform the public and keep people out while the plants get established.

I look forward to seeing how they manage the area over time and hope that other communities take steps to improve their streams as well.

May 2024 Moment in Nature

This week I walked back to the back of my property where there is a small creek. As I walked back, I noticed a bright flash of yellow in the creek; it was a male American Goldfinch and he had just landed for a bath. I froze for a moment to watch (and carefully pulled my phone out of my pocket, of course).

American Goldfinch in creek

He splashed and preened for a few moments and then took off. It was so special to see a wild creature in an unguarded moment. 

These #momentinnature posts are always fun to share and I hope it inspires you - even if just for a day - to spot something in nature that makes you glad you were there to see it.