By Ash Keiper-Kintz, Biological Science Technician at Cape Hatteras National Seashore
The Battle
When you look out over the saltmarsh at South Point Road on Ocracoke Island, you may think it looks calm and peaceful. But in reality, the seemingly passive plants rippling in the sea breeze are in the midst of the fight of their lives. This is the scene of an invasion in progress.
The majority of the vegetation you see towards the beach end of the ramp and spreading out towards the inlet are native grasses, sedges, and rushes, like Spartina species and Black Needlerush. They form a complex patchwork, dotted with shrubby cedars, the occasional taller spikes of Swamp Sawgrass, and fluffy white seeding Groundseltree Bushes.
But nearer to the village we start to see patches of another plant — first small, isolated stands, and then massive ones covering acres as far as the eye can see. It might seem innocuous, just another plant among the others. But this is actually our main enemy in maintaining native coastal ecosystems, Phragmites australis, innocently called the Common Reed.
And Ocracoke Island is a perfect visual example of invasion happening before our eyes.
What makes an invasive, invasive?
The distinction between non-native and invasive species is crucial when assessing their impact on ecosystems. Not all non-native species become invasive, but some possess traits that allow them to outcompete native species and dominate their environments.
Invasive plants, such as Phragmites, often reproduce rapidly through mechanisms like rhizome (root) division. For instance, when Phragmites runners are severed, both fragments can grow into new plants, making manual removal almost impossible and necessitating chemical treatment. This adaptation allows Phragmites to thrive in disturbed areas near human habitation.
Moreover, invasives usually lack natural predators in their new habitats, allowing unchecked growth. True invasives do not merely coexist with native species but actively displace them, causing ecological harm. This process, known as competitive exclusion, eliminates native biodiversity, creating monocultures dominated by the invasive species.
Another mechanism, called the priority effect, occurs when invasives quickly colonize barren areas, such as mudflats, and create a habitat that isn’t conducive to other species, preventing slower-growing native plants from establishing themselves. As fresh areas of silt build up and add on to existing sandbars in the estuary, invasive species that can colonize quickly and exclude others triumph in competition. This can also displace native animal species like Diamondback Terrapins which require those barren sand and mud flats to nest. A prime example yet again, Phragmites grows tall, shades out competitors, and maintains its dense, persistent stems even during dormancy.
Such invasions undermine the deep importance of biodiversity. Native plants and wildlife have evolved together in competitive balance, supporting a diverse array of flora and fauna. Coastal wetlands with native plants host a rich patchwork of species that provide food and shelter for wildlife. By contrast, monocultures of invasive species like Phragmites fail to support such biodiversity, leaving native species without resources.
Why do we need native species?
Many of the insect species in our coastal habitats are intrinsically tied with specific native plant species. For example, when you hear “save the bees” you might automatically think of Honeybees, but in fact the honeybee is not native to North America. Instead, this is referring to native species that are declining as native plant species they rely on are lost.
Around a quarter of the native bees in the eastern United States are what we call “pollen specialists,” meaning they only forage for the pollen of specific host plants. Here in coastal North Carolina, some such bees are the Morning Glory Bee and the Rose-mallow/Hibiscus Bee, which forage exclusively on the plants for which they are named. The many Swallowtail Butterflies we see at Cape Hatteras National Seashore also rely on plants like Swamp Rose-Mallow as hosts for both the caterpillar and butterfly stage, and the pollen supports beetle specialists like the Hibiscus Seed Beetles. Swamp Milkweed is another important species for our native Monarch Butterflies, and our many native flowers are crucial as they make their way south to Mexico during migration.
One of the fluffy bushes I enjoy most for its floating seeds (except when cleaning pony troughs) is the native Groundseltree. During the summer season I often shared the dunes with Groundselbush Beetles (like those pictured below).
Native plants also play a vital role in nutrient cycling and ecosystem health. For instance, native plants such as Spartina, Juncus, and Cladium help maintain water levels, and oxygenate both soils and water. In contrast, Phragmites consumes more fresh water than native species and traps excess nitrogen in its tall, dormant stems, disrupting the nutrient balance and reducing nitrogen availability for other plants. The delicate balance of nutrients in the estuaries is essential to our future fish populations, as these areas play nursery to many of our fish species as juveniles.
Controlling invasive species is vital to protecting these ecosystems. Prevention is key, and one of the most effective strategies is avoiding the introduction of invasives through landscaping.
Instead of planting non-native ornamentals that become invasive like Rattlebox and Mimosa, native alternatives like Swamp Rose-Mallow and American Beautyberry could be used. The striking fall colors of Muhley Grass provide great curb appeal and are a favorable local alternative to the non-native Pampas Grass. These plants are not only aesthetically pleasing but also better adapted to local pests and provide essential resources for native wildlife in the form of fruit and flowers.
For those desiring a traditional ornamental, many cultivars of Crepe Myrtle are sterile, and thus cannot become invasive. Do your research and check out local native plant organizations for recommendations! One of the shrubby trees you can find most prevalently in the Seashore’s coastal ecosystem is the Eastern Red Cedar. It hosts a variety of native insects, such as the Evergreen Bagworm, the larval stage of a native moth which often kills non-native ornamental evergreens, while only inhibiting native ones. Eastern Red Cedar is also important to native moth species such as the Juniper Hairstreak and the Imperial Moth.
What to do after the invasion?
When all else fails and an invasion occurs, it’s time for control options. Control is generally sorted into mechanical and chemical. Often the most effective plan is a mix of both methods. Effective control plans take years of repeated treatment to halt current invasives and prevent re-colonization. Different species and different environments require unique plans for control.
For instance, woody plants like Rattlebox are best controlled through what we call “cut stump” treatment, where we cut the shrub and then treat only the bare stump tissue with chemical. This makes it easy to be very precise in our use of chemicals, and limit overuse. We must plan to do this before the plants go to seed, their main dispersal method, to prevent recolonization during the growing season. Every year we have to re-treat the area as seedlings from older seeds in the seed bank sprout, but eventually, if we are able to prevent new seeds from being deposited, this invasion should be halted.
For larger woody species that can’t be as easily felled, like Thorny Olive and Mimosa Trees, girdling is another effective mechanical treatment. Girdled trees have a somewhat shallow ring cut into the bark encircling the tree. The cut is deep enough to interrupt the flow of nutrients, preventing the tree above the cut from surviving. To prevent the tree from regrowing from the roots, this is often used with chemical control methods such as stem injection.
Phragmites is an even more challenging foe. With its main method of dispersal being root division, any mechanical disturbance like pulling simply helps the plant propagate. And the tall, dense stands it forms can be daunting to say the least. Some stands can grow to over nine feet tall, and so dense that navigation by sight is impossible.
For stands like this, it’s necessary to remove as much plant matter from above the surface as possible to make chemical treatment effective. Controlled burning can also be an effective aid to this process. Although fire cannot kill the roots of the plant, burning aboveground organic material increases access for future chemical treatment as new leaves sprout. This is because the most effective way to control Phragmites is through “foliar treatment” which is the spraying of chemical on the leaves. This chemical is absorbed by the leaves, then travels through the plant’s vascular tissues to reach and kill the parts that were unreachable underground. Use of foliar spray is done with great care, as we want to make sure to only target the top 30 percent of each Phragmites plant without over-spraying onto non-target native plants and the water we are often working in. Monitoring wind direction and speed is important while we are deciding how and when to treat, as is the time of year when treatment will be most effective.
The sheer acreage to be covered when treating Phragmites on the Seashore is its own challenge. In many cases with limited crew sizes, invasive species management plans must simply focus on preventing further spread where possible while slowly reducing patch size year by year.
Is the treatment working?
The most important thing to realize about the process of invasive species control is that it takes time and continuous effort in order to succeed.
One thing I noticed this fall along Ramp 72 as the monarchs were landing and the goldenrod was in full bloom, was how much more Goldenrod coverage there seemed to be now that we were able to treat the Phragmites along the ditches. As expected, every area where I treated and removed mature Rattlebox plants the previous season had new seedlings, but those seedlings can be managed before maturing and reseeding themselves. And those seedlings were in some cases being outcompeted by native plants!
Each year and each new growing season provide new opportunities to continue boosting native plants and reducing the impact of invasives in our delicate and beautiful coastal wetlands. We will continue to fight to preserve these essential habitats, much of which is only possible through donations and donor funds like the Aid to Parks Fund, which allows us to get larger temporary crews through programs like American Conservation Experience (ACE), as well as tools and chemicals to carry out treatment.
While I have only been the career-seasonal on Ocracoke Island for two years, I have fallen in love with the sight of the sunrise over the saltmarsh and the calls of Marsh Wrens, Red-Winged Blackbirds, and the occasional startled Egret as I walk along South Point Road. I have yet to have a day on the island where I didn’t find something new and beautiful to photograph. I hope to keep those views and the myriad native species that call this place home safe as I continue my work here for seasons to come.
About Ash
Ash has been a ranger here at Cape Hatteras National Seashore for seven years, five as a seasonal in Buxton and now as a permanent on Ocracoke Island. Before that they worked at various national parks, national forests, and national wildlife refuges across the country, from Oregon and Idaho to Utah, to South Carolina and Georgia. An avid bird lover, Ash came for the shorebirds but has come to love and appreciate the turtles as well. They enjoy photography, fishkeeping, and kayaking in their spare time.
Photo Credits
- Photos 1-3: National Park Service – Cape Hatteras National Seashore
- Photo 4: P. Doshkov
- Photo 5: A. Gause
- Photo 6: M. Jansen
- Photos 7-10: A. Keiper-Kintz
- Photo 11: M. Maturen
- Photo 12: A. Keiper-Kintz
- Photos 13-15: National Park Service – Cape Hatteras National Seashore