Native, Invasive, Weed, or What?
Habitat Enhancing Land Management
Christine Middleton
Spring is just around the corner. Tenpetal Anemone, (Anemone berlandieri) is already blooming. Despite the name, this early bloomer does not have petals. Rather, those ten or so things you see that look like white or purple petals are sepals. Sepals are modified leaves designed to protect the flowering part of the plant. Soon, the Tenpetal Anemone, also known as “Windflower,” will begin producing seeds that blow away in the wind. Deer will nibble on the leaves but generally leave the flowers alone, likely because Windflowers are toxic if eaten in large quantities.
Get to know the plants on your property. Why? It’s lots of fun. But that isn’t the only reason. As you learn more, you will begin to understand the role vegetation plays in your little piece of the ecosystem. Is the plant you found a host for butterflies? If so, what kind of caterpillars does it nourish? Which birds feast on its seeds or berries? Did it arrive from someplace far away, and if so, is it a well-behaved foreigner or a destructive invader? The answers to these and many other questions will help you as you work to improve the health of your beloved property.
But what do all those terms mean?
Do you know what it means when a plant is labeled native? Or when someone says a plant is invasive? And what are weeds anyway?
The USDA defines a native plant as “a plant that is a part of the balance of nature that has developed over hundreds or thousands of years in a particular region or ecosystem.” In other words, species designated as native must have gotten to where they are on their own—without human intervention. Sometimes the terms native and indigenous are used interchangeably. Native simply means that the plant grows within your ecoregion. Indigenous means it is growing on your property without any action by you or previous property owners.
Endemic is another term you might hear applied to native plants. Endemic means the species grows only in a specific area and nowhere else. For example, Texas Bluebonnets (Lupinus texensis) are endemic to Texas. Given the right conditions and a bit of human intervention, they might be encouraged to grow elsewhere. But outside of Texas, bluebonnets are considered a non-native species.
The area across which a plant is endemic can be even more concentrated, say just in the Texas Hill Country. For example, according to the Ladybird Johnson Wildflower Center’s plant database, our Escarpment Black Cherry (Prunus serotina Ehrh. var. eximia) “is a distinct and isolated geographic variety of Black Cherry found only in the calcareous soils of Central Texas.”
Escarpment Black Cherry Photo: Constance Quigley
Non-native (alien, exotic) plants are the
logical opposite of natives. Through
some form of human intervention, non-native
plants have come into new places
or habitats where they were not
previously found. Also termed
introduced, Central Texas non-natives
by definition have come from somewhere
else, likely within the last two hundred or
so years. It doesn’t matter whether their
introduction was intentional or accidental.
Some non-natives, such as Oxblood
Lilies, have been here long enough to
become well-established within their new
environment. Such plants are said to
have become naturalized because they
can now grow on their own here without
requiring amended soil or extra water.
Native vs. Non-native
Oxblood lilies were imported from Argentina to Central Texas about 150 years ago by German immigrants. These delightful, ephemeral flowers are also called “schoolhouse lilies” because their blooms always appeared just as 19th-century schools were about to re-open in the fall. Oxblood lilies are naturalized here but are not invasive. Given their bright red color, they do attract bees and hummingbirds. But they only bloom for a week or so in early September. And it is not clear whether they have any real value for pollinators as they and the pollinators didn’t evolve together. And that’s the problem. Animal species often show a strong preference for the plants native to their part of the world. They may even have evolved together.
Eastern Bluebirds and Summer Tanagers forage caterpillars for their nestlings.
In his book, Nature’s Best Hope: A New Approach to Conservation That Starts in Your Yard, Doug Tallamy talks about a study one of his graduate students did. She found that Chickadees—like so many of our songbirds and migratory birds that nest here—apparently choose their nesting sites based on the availability of food. Most set up their nests in suburban yards where caterpillars, the most nutritious food for their hatchlings, are readily available. Not coincidentally, these are also the yards with the most native plants.
But that’s not all. She found that when they did put their nest in yards with lots of introduced (non-native) plants, the nests had fewer eggs, and the nestlings were less likely to survive. They simply weren’t an evolutionary match.
Another difference between native and non-native is that native plants have evolved with our climatic conditions. Some of our central Texas non-natives come from places with similarly dry climates and are labeled as “drought-tolerant.” But many coming from wetter, milder climates may require more water, cooler summer temperatures, or warmer winters to thrive. Anecdotal evidence suggests that during our most recent drought, native species fared much better than non-natives.
So our hardy natives may die back to the ground during hard times, but we are often surprised by the fresh green shoots that pop up as soon as favorable conditions return.
Aggressive Native vs. Weed vs. Invasive
Many of our native plants have the word weed in their names, such as Milkweed, Frostweed, and Roosevelt Weed. Often these are species that thrive in disturbed areas. Often they are plants unwanted by farmers whose livelihoods depend on seasonal planting—periodically disturbing their soil. But many of these “weed” species also have important ecological functions. And what about all the different kinds of Milkweed that are essential for Monarch reproduction when the butterflies return to lay their eggs in the spring?
Milkweed is critical to one of our most cherished and vulnerable butterflies—the Monarch. Milkweed serves as both a nectar source and a host plant for migrating Monarchs and their caterpillars. In this photo, Antelope Horns Milkweed provides nectar to a migrating Monarch who has just arrived. (Jacob’s Well Natural Area - April 12, 2020).
In the spring, migrating Monarchs lay their eggs on milkweed leaves. When the caterpillars hatch, they consume the plant before pupating and transforming into adult butterflies. The newly emerged butterflies travel north, seeking more milkweed plants along the way and continuing the cycle until the third and fourth generations reach their summer destination in the northern U.S. and southern Canada. In the late summer and early fall, a final generation is born. These adults fuel up with nectar and begin their return south.
As the migrating Monarchs pass through Central Texas in the fall, they seek nectar from Frostweed and other flowering natives, such as Roosevelt Weed. They need significant fuel to get them back to their overwintering grounds in Mexico, where they will cluster together until early spring and begin the cycle all over again.
Both Roosevelt Weed (Baccharis neglecta) and Frostweed (Verbesina virginica) provide nectar for migrating Monarch butterflies and other pollinators in the fall.
Frostweed provides nectar to many fall butterflies. These are Queen butterflies.
Roosevelt Weed attracts pollinators of all kinds. This one is literally buzzing and vibrating with life.
“Aggressive natives,” such as Roosevelt Weed, are native species that spread rapidly and come to dominate a disturbed area. Often they are the first step in what is called ecological succession.
Ecological succession is a good thing! It refers to the process by which natural plant communities replace (succeed) each other over time. At each stage the community of plants creates conditions that enable future plants in a subsequent community to survive. Ultimately, the plant community reaches a climax stage, which remains stable until the next disturbance.
Native Sycamores pioneer ecological succession after a flood event.
Riparian areas along streams are frequently disturbed by flood. First come the “pioneers”—plants such as Sycamore (Platanus occidentalis)—that are the first to take hold, given their ability to survive harsh, post-flood conditions.
Pennywort and Spike Rush colonize a stream.
These are followed by “colonizers” such as Pennywort (Hydrocotyle ranunculoides), which spread quickly. The mat of roots they put down catches sediment. And the sediment trapped by these colonizers sets up the next stage for the taller, deeper-rooted plants, such as Switchgrass (Panicum virgatum). These late-stage plants, called “stabilizers,” establish more slowly. But once established, their deep roots provide protection from future flooding events.
Some people incorrectly label these natives that take over disturbed areas as “invasive.” A better way to describe them is “aggressive natives.” Eventually, as ecological succession proceeds, they will be outcompeted in some way by later succession species. They might be shaded out by taller species. Or as soil builds and holds more moisture, they may simply decide conditions are no longer to their liking. But this often takes a long time, and we humans are an impatient species. One alternative is to jumpstart recovery by introducing a wider array of species into a disturbed area to prevent the native early arrivals from taking over.
Non-native Johnsongrass invades the flooded out bank of the Blanco along River Road in Wimberley. Photo: Mimi Cavender
Invasive plants, too, like disturbed areas. But, unlike aggressive natives, they often lack redeeming ecological value and are unlikely to eventually die out on their own. They are also prone to spreading beyond their initial niche. Many invasive plants, such as King Ranch Bluestem (“KR!”), produce large quantities of seed; Johnsongrass spreads by runners.
Invasive Giant Reed (Arundo donax) appeared in Wimberley’s stretch of the Blanco River after 2015’s Memorial Day flood carried broken pieces of it from far upstream. Photo: Mimi Cavender
An extremely invasive species, Arundo donax, non-native Giant Reed, spreads from pieces—even just a leaf—broken off the plant by floods or mowing. Arundo also spreads voraciously by airborne seeds and by its thick rhizome mats in wet river bottom or in nearby riparian soils—a fast-colonizing triple threat that will eventually affect stream flow. If your property has river frontage, look for Arundo. Read about its safe eradication in Reed It and Reap in the October 2022 Hays Humm.
Now let’s be sure we get the worst of these terms straight. The most misunderstood of this plant vocabulary are the terms invasive, weed, and noxious weed—Yikes!
As we’ve seen, to be considered invasive, a plant must be both non-native and disruptive. That implies that the foreign species spreads in ways that interfere with native plant and animal species. The term weed is independent of origin and simply implies the plant is unwanted. But unwanted is a subjective term as one person’s weed can be another person’s flower! A noxious weed is any plant designated by a federal, state, or local government agency as injurious in some way to public health, agriculture, recreation, wildlife, or property.
Ligustrum
Photo: Scott Peterson
Invasive non-native Nandina along Cypress Creek in Wimberley.
Photo: Mimi Cavender
Some non-native landscaping plants produce berries that are spread by birds. In our part of the world, Ligustrum (also called Privet) and Nandina (also called Heavenly Bamboo) often make their way out of our gardens and into our natural areas with the help of hungry birds.
And what makes invasives so successful? It’s usually not just one factor, but a combination of things that enables the introduced species to win the battle for space.
In their book, Unnatural Texas? The Invasive Species Dilemma, co-authors Robin W. Doughty and Matt Warnock Turner explain how “quirks of geography, climate, peculiar growing habits; freedom from native predators; and economic promise all converge to create an invasive dynamo.” They are talking about what is undeniably a beautiful tree—Chinese Tallow. They go on to illuminate how the combination of shared latitude, prolific seed production and root sprouting, soil indifference, and freedom from predators all combine to make this foreign tree so successful.
Non-native invasive Chinese Tallow displays bright fall colors, but branches are brittle and easily break.
Need Help?
Spring flowers mean many of the plants blooming on your property will be easier to identify. iNaturalist is a great application that helps you to do just that! And once you’ve identified them, you’ll want to know more. Lots of on-line resources can help! Our two favorites are the databases of Lady Bird Johnson Wildflower Center and the Native Plant Society of Texas (NPSOT).
“To love a place is not enough. We must find ways to heal it.” ― Robin Wall Kimmerer, Braiding Sweetgrass
Want more help? As part of our HELM (Habitat Enhancing Land Management) program, we will send a team to walk your property with you. We’ll identify plants and give you hints on using iNaturalist. We’ll talk with you about any invasives we find and help you figure out the best way to manage them. And lots more! We currently have a few slots left in our Spring 2024 schedule. So if you or one of your neighbors would like the HELM team to visit your/their property, simply go to https://www.beautifulhayscounty.org/helm/ and fill out our request form. And please help us spread the word!