By Eileen Berger
What if I told you that Texas is under invasion from foreigners that threaten to crowd out our native species, with untold damage being done right now? Don’t call out the armed forces, because the invaders aren’t human. They are plants. Some were introduced to the U.S. to be used as ornamental shrubs or trees, while others were brought here to solve problems of feed for cattle or erosion control. Marilyn Sallee, the regional director for texasinvasives.org presented these interesting facts to members and guests at the monthly meeting of the Indian Trail Master Naturalists.
To be labeled an invasive species, first the plant must be foreign to the ecosystem where it is growing, either brought from another country, another part of the United States or even another part of Texas. Some of our native species can be aggressive growers, as anyone who has grown trumpet creeper knows very well. However, even trumpet creeper does not completely cover and choke out nearby plants, as does the dreaded kudzu (Pueraria montana). Alas, it seems that kudzu has been found in Ft.Worth, which is closer than we like to imagine. So, do not confuse invasive with aggressive.
Some of the threats from invasives stem from the fact that these plants are very well suited to living in our climate and they are easily spread. They tend to form monocultures, meaning that the only plant you may see in an area is that one plant. They are so successful, and so vigorous, they crowd out our native species. Why is that bad, you ask? Native plants are important because they are part of the unique ecosystem of a particular area. Those plants and the animals that use the plants are interconnected in such a way that each plant or animal benefits the others. It is like a house of cards. If you remove one card, the house collapses. From the tallest oak tree to the microbial level of plants and animals, everything is interdependent.
Some of the worst offenders in our area of Texas are members of the Ligustrum family, or privet. These are easily spread by seeds dropped by birds. Saltcedar (Tamarix spp.), is especially destructive because it is able to pull so much moisture from a creek or river that it can actually cause the river to dry up. The Tree of Heaven (Ailanthus altissima) actually poisons the soil it grows in, causing other plants to die. Giant reed (Arundo donax) grows in ditches eventually clogging the waterway so that in a downpour the water is diverted to a less desirable area, causing erosion. Don’t even think about planting bamboo, no matter how exotic it would look in your Japanese water garden. There are no giant pandas here in Texas to keep it in check. Gardeners wishing to have a nice lawn spend hours and dollars trying to eradicate three invasive pests: Nutsedge or nutgrass (Cyperus esculentus), dallisgrass (Paspalum dilatatum) and Johnson grass (Sorghum halepense). Yes, they are all foreign. Texas does have laws prohibiting the growing or introduction of a group of invasive plants that grow in water, among them giant salvinia(Salvinia molesta) and water hyacinth(Eichhornia srassipes).
One problem with invasives is that some of them are pretty. Who doesn’t love the purple blossoms of Chinese wisteria (Wisteria sinensis) or chaste tree (Vitex agnus-castus)? Further, gardeners can argue that they don’t see any volunteer wisteria or chaste trees in their neighborhood. They may be right. However, privet was not a problem for a hundred years in Texas. It was not until the 1950’s that it got out of hand here. Hindsight is always better than foresight. Now nurserymen, foresters and agronomists are much more cautious than before. There are citizen scientists on patrol looking for the invasives, reporting them to watch groups such as texasinvasives.org. For more information on invasives, check out their website, Texas Invasives.