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INVASIVE
SPECIES
As
gardeners we should strive to be aware of plants that may cause problems
in our particular environment.
To most people, the word invasive raises a red flag as a plant that could
cause problems
in the home landscape. For example, nutsedge in the lawn would be considered
an invasive species. However, as defined by Texas Parks & Wildlife,
the EPA, and other environmental groups, the term "invasive species" refers
to foreign plants that have increased in the wild to the point of choking
out or displacing our indigenous native species. Ironically, in this
case the nutsedge being a native found in the wild would not be considered
invasive. Bermuda grass (originating in Africa) would be considered invasive
instead.
This example will likely raise a few eyebrows among homeowners as bermuda
grass has long been considered a good choice of lawn grass and a staple
forage crop
in agriculture. In fact, it seems our Texas Department of Agriculture actually
encourages the cultivation of bermuda as one of the easiest ways land owners
can receive tax exemption for agricultural land use. Likewise, our local nursery
professionals and extension agents continue to tout the virtues of bermuda lawns.
Yet, if you research the "weed lists" or "invasive plants" listings
on the A&M or TDA websites you will sure enough find bermuda grass listed
as a noxious weed. Go figure.
In reality, as gardeners we all can testify to the stubborn invasive nature of
bermuda grass when we try to keep it out of the flowerbed or when we attempt
to eradicate a patch to plant something else in its place. This gardener has
actually observed bermuda in road ditches out in the Chihuahuan Desert where
rainfall averages less than 10" per year. This is irrefutable evidence
of the sheer tenacity and drought tolerance of this foreign grass that was brought
here with every good intention but has spread itself into places where it should
not be.
The term "invasive" is a scary one to most people. If you call a plant
invasive it is almost sure to make your friends and neighbors think twice before
using it in their landscape. But, when you think of it, most of the plants we
use as groundcovers have an invasive nature. How else could they have that ability
to get out there and cover the ground quickly? Just how invasive a plant may
be is relative to your local environment.
 A good example of this would be ground ivy or gill ivy (glechoma hederacea).
Ground ivy is a fast growing ground cover that does not climb (hence the name),
stays evergreen, and grows to only a few inches tall. Because of these obvious
attributes, ground ivy comes highly recommended by several leading horticulturists
here in Texas. However, if you contact a horticulturist from the milder climates
of the east coast, you will certainly be warned that this European invader has
caused all sorts of problems by choking out sensitive native plant communities
in forested areas.
You can research invasive plants of Texas on the web by visiting our Texas Department
of Agriculture (www.agr.state.tx.us/ <http://www.agr.state.tx.us/> ), Texas
A&M (texasextension.tamu.edu/), and Texas Parks and Wildlife (www.tpwd.state.us <http://www.tpwd.state.us> ).
One of the better sites for the entire U.S. is the Plant Conservation Alliance
at nps.gov/plants/index.htm. As you peruse these various lists you will be amazed
at just how many of the common plants we use as ornamentals are considered invasive
in various parts of our nation. You will also find that the strict definition
of an invasive plant is simply any non-native plant that has escaped cultivation.
All native plants are exempted from these lists regardless of how invasive (trumpet
vine (campsis radicans), for instance) they may be in the home landscape unless
they are taken (presumably by humans) out of their native habitat and introduced
elsewhere.
So what should a gardener who is also concerned about environment (that includes
most of us) do? Should we refuse to plant any or all of these invaders? The choice
is bewildering when you consider the fact that most of the plants we see in the
traditional nursery system originated in Europe, Asia, or the Mediterranean.
The answer lies in understanding just what plants are capable of reproducing
themselves in your particular part of the state. For instance, the Chinese tallow
tree (sapium sebiferum) is taking over creek banks and low areas from Houston
to Beaumont and points east. However, here in northern Texas, the tree cannot
survive due to our colder winters. In fact, here in my hometown of Wichita Falls,
Chinese tallow has a poor chance of survival even with the help of a diligent
gardener. On the other hand, I have noticed Japanese privet (ligustrum japonicum),
and Japanese honeysuckle (lonicera japonica) are gaining a foothold along our
streams and rivers especially near populated areas. So the astute gardener discovers
that what may be invasive for some might be benign in his or her local area.
The nursery industry could play an important role in educating the public by
steering customers toward better plant choices but this, unfortunately, has not
been the case. In fact, the nursery industry itself has been responsible for
many of these plant introductions. If you are among those who have a local nursery
with an "environmental consciousness," please support their efforts
and encourage others to follow suit.
Currently our state does have laws in place concerning the sale of some aquatic
plant species. We could and perhaps should put some parameters in place regarding
the sale of invasive dryland species as well. One of the fastest growing segments
of land use has been the reclamation of indigenous plant populations. Efforts
have been made by the Ladybird Johnson Wildflower Research, the Native Plant
Society of Texas, The Nature Conservancy and a host of like-minded organizations
too numerous to mention here. All of the people who have been involved in land
reclamation projects will agree that it is extremely difficult if not impossible
to return land to its pristeen state because of the number of introduced plants
that are firmly entrenched in the environment. The first logical step must be
to prevent the introduction of even more. Only then can the attempts at eradication
have a positive impact.
Plants have no way of understanding where we want them to grow and where we want
them to stop. They simply do what they do. At present there are no herbicides
that can distinguish the invaders from indigenous plants. In some instances such
as lawn grasses, ground covers, and vines used to cover unsightly areas, invasiveness
can be very desirable. In other cases, introduced plants such as kudzu, hydrilla,
and salt cedar have been devastating and are costing us as taxpayers untold millions
in habitat loss. The best course of action for us as concerned citizens is to
familiarize ourselves with potential problems and curb our own use of invasive
plants then spread the word to others. We also should support legislation that
will curtail the import of more invaders. Some states have already taken action.
Texas will follow suit. If you have questions or doubts, contact your local extension
agent, Parks & Wildlife representative, or botanist. Know what you are planting
before you plant.
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