Alamo Area Master Naturalist Jessica Leslie is the author of this piece.
Note: This notice is required by HB 338, passed by the 2011 legislature. Any plant termed below as an invasive “is only a recommended [characterization] and has no legal effect in the State of Texas. It is lawful to sell, distribute, import or possess a plant [we term invasive] unless the Texas Department of Agriculture labels the plant as noxious or invasive on the department’s plant list.”
The term invasive species is formally defined to mean a species which is not native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm, or is a threat to human health.
INVASIVES DRIVE OUT NATIVES
Exotic invasive plants are those plants that are not native to an area but reproduce so readily that they establish themselves very quickly. Their rapid spread often causes harm to the environment by outcompeting the native plants in an area.
A casual stroll through almost any city or state park will reveal the extent of the problem. Many parks contain hosts of invasive species. Some are even overrun by exotics so much so that native species are nonexistent in large swaths of our once native areas.
SO, WHAT IS THE PROBLEM?
The problem lies in the fact that other native species, such as insects, birds, etc., have evolved to rely upon native plants as a source for food and shelter. If the invasive plants dominate an area, the native plants cannot survive. They are literally choked out of the ecosystem due to competition for sun and water. Without the natives, the insects and other species lose their food and shelter sources, and they, in turn, also cannot survive.
It literally works like a chain reaction—cut out the food and shelter that native plants provide, and all wildlife dependent upon those plants must move on or perish. If enough of our native habitat is replaced with exotic invasive plants, then our native wildlife begins to disappear. The staggering number of native species (both plant and animal) that we are losing every year is a testament to that fact.
INVASIVES ESCAPE THE CONFINES OF OUR YARDS
How did these invasive plants get here? Many of these plants were imported from other countries for their ornamental value and their resistance to insects and disease. Nurseries sell them as landscape plants, but, unfortunately, they do not remain in the confines of our yards. When they show up in natural areas, they have few natural predators, thus they are able to continually reproduce without predation. The added fact that they are generally disease- and insect-resistant only increases their survivability.
When exotics take over an area and choke out natives, animal species such as birds and insects no longer have a natural food source in the area, and so they move on. If an invasive plant becomes persistent over a large area, some animal species could become endangered or simply disappear. The end result is that native habitat becomes overrun with exotics, and not only do our native plants disappear but so do many of our native animals.
It is true that some of the invasives provide tasty berries for some birds. Unfortunately, that just helps the plant’s spread. It is also true that some exotics provide berries that are actually toxic to some birds (check out the die-off of dozens of cedar waxwings who ate nandina berries (Nancina domestica) here).
KING RANCH BLUESTEM IN PHIL HARDBERGER PARK
Volunteers working with city staff have removed many of the invasives from Phil Hardberger Park (West). The park is relatively free of invasives with the exception of King Ranch Bluestem, which is difficult to eradicate. King Ranch Bluestem (Bothriochloa ischaemum var. songarica) is a grass introduced from Europe and Asia as livestock foliage and for erosion control, mainly along roadsides and highways. It established itself very quickly and is now present in many parts of the state, leading to the local demise of our native grasses such as Little Bluestem (Schizachyrium scoparium) and Sideoats Grama (Bouteloua curtipendula).
SO MANY OTHERS
Other exotic invasives that have found their way from our backyards into our natural areas include:
- Nandina (Nandina domestica)
- Chinese Tallow (Triadica sebifera)
- Chinaberry (Melia azedarach)
- Ligustrum or Privet (Ligustrum lucidum)
- Lantana (Lantana camara), not to be confused with Texas Lantana (Lantana x urticoides)
- Bastard Cabbage (Rapistrum rugusum)
- Malta Star-thistle (Cenaurea melitensis)
HOW MAY THE AVERAGE CITIZEN HELP CONTROL THE SPREAD OF INVASIVE PLANTS?
There are at least four major things you can do to have an impact:
- Learn about specific invasive species in your area. Then learn about the native species for your area. A good starting place is in the links below. Another good source is your area’s Native Plant Society and your local Master Naturalist group.
- If you live in the city, turn your yard into a native habitat. Remove the exotic invasives and plant natives. If every yard in your city were converted into native habitat, the amount of native habitat would grow exponentially, and native wildlife would thrive there. If you are a rural dweller, simply remove the invasives from your property and allow the natives to prosper unless your property needs restoration efforts.
- Talk to your friends. Show off your yard, including the diverse species you are now attracting.
- Volunteer. Join a group dedicated to removing exotic invasives in your area parks. It is amazing what an impact that has.
For wide-ranging generalized information on invasive species see Texas Invasives
For focused specific information on invasive species at our Natural Areas, especially Phil Hardberger Park (West) see Area Invasives.
For material for children see Exotic Invasive Plants.