Hill Country Naturalist

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Invasive plants to avoid in the Hill Country

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World-wide, invasive species are second only to habitat destruction (for development and farming) as the cause of the loss of species. It is estimated that the US spends over 100 billion dollars a year fighting invasive species. The Hill Country has, so far, been spared some of the worst examples of invasives experienced by other parts of the country.

We don’t have, in large amounts, the kudzu of the southeast, the Asian carp of the Midwest, the zebra mussels of the Great Lakes, the Buffelgrass and Guineagrass of the Rio Grande Valley, the Cheatgrass of the western plains, or the Tamerisk of our western rivers. So far as I know, Giant salvinia has not made it to any of our local lakes--yet.

The legal definition of an invasive species is, “An alien species whose introduction does or is likely to cause economic or environmental harm…”. Exotic, or alien, plants are introduced into this country either for the nursery trade, for agricultural purposes, or accidentally. Most of these plants do not become invasive, or are not invasive in the part of the country in which they are originally introduced. But certain species, and it is impossible to predict which ones, do become invasive, and they grow and reproduce so prolifically that they escape where they were originally planted and crowd out native vegetation.

This invasion of introduced plant species results in a decrease in the population of certain native species, thus changing the balance of vegetation in the ecosystem. Species of insects or other animals that depended on the displaced plant species may disappear. Or the introduced plant may be utilized by different species, thus upsetting the balance of nature, so the diversity, the health, and the productivity of the ecosystem may be diminished.

A non-native plant found growing anywhere it was not originally planted is, or likely will become, invasive and should be avoided for the protection of our native habitat. Here are some of the worst offenders.

For trees and shrubs, the worst are Chinese tallow, Chinaberry, Ligustrum, Tree of Heaven, Paper mulberry, Golden raintree, Salt cedar, and Vitex. Chinese tallow and Chinaberry are already taking over large stretches of the Guadalupe River banks and are increasingly seen throughout our area. Ligustrum is nearly ubiquitous in and around Kerrville and is a very strong competitor with our native plants. The Tree of Heaven is a very fast-growing tall tree which produces huge quantities of seeds, many of which produce numerous shoots in the landowner’s lawns, but worse yet, are beginning to move out into the country. Vitex has almost totally choked off access to parts of upper Lake Buchanan.

For some years, it was thought that Chinese pistache, while it grows well here, was not invasive. There has been some recent evidence, however, that that may not be the case, and we may be seeing it escape from people’s yards into natural areas. It is not uncommon for plant species to take many years to become invasive, as first the trees must reach reproductive age and the population necessary to become invasive.

Among the other worst invasives in this area are the Giant reed, (Arundo donax) which has taken over large stretches of Town Creek and various other creeks in the area, crowding out all other vegetation. Other offenders include Cocklebur, Bamboo, Nandina, Japanese honeysuckle, Musk thistle, Johnsongrass, and Bermudagrass.

Probably the most widespread invasive plant in the Hill Country, one that is present on nearly every ranch and ranchette, is King Ranch bluestem. In past years TXDOT planted lots of KR bluestem along roadsides to prevent erosion (fortunately, they now mostly use native grasses). Whether or not KR is better at that than some native grasses is questionable, but at any rate, it has spread from roadsides to almost everyone’s property. It is most prevalent in moderate to heavily grazed pastures where it takes over from native grasses and is exceedingly difficult to remove.

So, the bottom line here is to avoid exotic plants that are known to become invasive and be cautious about any newlyintroduced species as we never know what can become invasive. There are lots and lots of native plants which grew up here, belong here, and never cause any problems. So, let’s stick with these natives; they are easy to grow, don’t cause problems, and don’t need extra water or fertilizer, and the native birds and insects like them very much.

Happy Thanksgiving everyone; stay safe and protect your friends and neighbors.

Until next time…

Jim Stanley is a Texas Master Naturalist and the author of the books “Hill Country Ecology,” “Hill Country Landowner’s Guide” and “A Beginner’s Handbook for Rural Texas Landowners.” He can be reached at <jstmn@ktc.com>. Previous columns can be seen at <www.hillcountrynaturalist.org>.