Invasive Plants

Most wildlife managers prefer native habitat, but most ranches now have a combination of native and non-native vegetation which still provides healthy habitat for many species.

A Commonsense Approach

Article by STEVE NELLE

What words come to mind when you think of kudzu? Even if you have never even seen kudzu, you have heard the stories and seen the pictures of what it can do. We all have our perceptions about invasive plants, but are they based on knowledge or hysteria?

Invasive species have become a battle cry for many environmentally minded Texans and a call to wage war against the invading species. Too often, the term “invasive” is used like a red flag to incite an emotional reaction rather than a wellreasoned response.

This article will encourage a balanced and logical perspective on the sometimes-heated topic of invasive plants and what we should do about them. Some people vilify and want to eradicate invasive plants, while others see the legitimate value they bring.

Both sides bring valid truth and neither side is always right or wrong. Most of us who live and work in the realm of land management appreciate native species but we have mixed feelings when it comes to non-natives and especially those that can cause problems.

Experts say that about 15% of the non-native species that find their way to the United States become harmful or invasive. Most of the non-native species do not cause problems and many of them are beneficial. However, it is good to remember that it may be decades before the invasive tendencies of a newly introduced species become apparent, and by then it may be too late.

CONFUSING TERMINOLOGY

The term “invasive” is widely used but not well understood. Everyone has their own idea of what an invasive species is but

there is no uniform designation of which species are invasive. Most people now agree that the term should be reserved for non-native species. However, it is still common for people to refer to mesquite, cedar, huisache, and other shrubs as being invasive even though they are native.

Nearly everyone does agree that invasive species are those that have a high potential to cause serious ecologic or economic harm. Most invasive plants have the potential to spread rapidly and to dominate and monopolize to the detriment of native species.

SOME COMMON SPECIES DESIGNATED AS INVASIVE BY TEXAS INVASIVES

WOODY PLANTS Chinese pistache Japanese honeysuckle Wisteria Macartney rose Leucaena Redtip photinia Pyracantha Siberian elm Mimosa

GRASSES Tall fescue Bahia grass Bermuda grass Buffelgrass Johnsongrass K R bluestem Kleberg bluestem Angleton bluestem Lehmann lovegrass Dallis grass Rescuegrass Mexican needlegrass

FORBS Yellow sweet clover Bur clover Dandelion Periwinkle Muellin Coral vine English ivy Horehound

The only official listing of invasive plants for Texas is kept by the Texas Department of Agriculture. The agency lists 28 species as invasive or noxious, with no clear distinction between the two terms. Under state law a person may not sell, distribute, or knowingly import any of these species.

Texas Parks and Wildlife Department also maintains a list that is geared specifically toward aquatic environments. That list contains 22 prohibited plants in addition to prohibited fish and shellfish that are considered invasive and harmful to Texas waters.

Two additional invasive plant listings are sometimes used although they have no legal status. Texas Invasives is a collaborative listing and information database of species that have been designated invasive by partner organizations. This listing contains 179 plant species classified as invasive. Texas Invasives also lists the “Dirty Dozen” invasive plants for each region of Texas.

The other unofficial listing is maintained by the Texas Invasive Species Institute in association with the Texas State University System and with the cooperation of several governmental and nongovernment collaborators. This listing indicates 91 plant species as being invasive.

So, which list is right or which one is best? Just how many invasive plant species are there in Texas? There is no clear answer, but regardless of what list is used, Texas is now home to a host of non-native plants that are considered by some to be harmful and undesirable.

THINK FUNCTION NOT ORIGIN

One common sense approach to invasive plants is to think about the function of the species rather than focus simply on its geographic origin or whether it appears on a list. Many of the species that are dubbed invasive have legitimate and useful ecological functions and benefits even though they can also cause problems.

Does it protect soil? Does it enhance soil organic matter? Does it provide browse, berries, seed, nesting cover, or fawning cover for wildlife? Does it provide forage for livestock? Does it produce nectar or

Sometimes planted for its striking fall color, Chinese tallow is considered an invasive and can become a serious problem in some places.

pollen for native insects? Does it help stabilize creek bottom areas? Does it have aesthetic or economic value?

MANAGEMENT BACKFIRES

We must be careful that we do not inadvertently do more harm than good when attempting to control invasive species. Sometimes we become so focused on killing invasives that we do not think clearly about the possible side effects. For example, using fire to suppress Lehmann lovegrass will often cause it to increase.

The control of buffelgrass can cause an increase in Kleberg bluestem, which is considered a worse problem. The overly aggressive control of dense ligustrum or salt cedar in riparian areas can result in accelerated bank erosion. An invasive plant may be doing more good than harm when it is left intact and we can cause a worse problem by trying to control it.

MISLEADING INFORMATION

Some invasive species are so strongly detested that detractors are guilty of exaggerating the negative characteristics as a way of inciting others to dislike the species. For example, it is common

Photo by Russell A. Graves

Photo courtesy of Kay Ledbetter, Texas A&M University

Sometimes it takes an invasive to deal with an invasive. The salt cedar beetle was brought in as a natural control method for tamarisk, which can overtake river bottom habitat.

K R bluestem is the most widespread and notorious of the exotic grasses. While it does provide good forage during the growing season, it has become too abundant in many places.

Non-native grasses are not a biological desert. Here a turkey is seen feeding in a thick stand of Kleberg bluestem. Astute grazing managers can use targeted livestock grazing to reduce the abundance of invasive grasses without harming the native grasses.

to hear native plant enthusiasts proclaim that K R bluestem provides exceptionally poor grazing. However, most ranchers who have K R bluestem or its relatives consider it a valuable forage grass during the growing season and are glad to have it.

Giant reed, also called Carrizo cane or Georgia cane, is another species harshly denounced by critics for causing extreme problems in riparian areas. This kind of overstated rhetoric spreads fear and dislike of the species and helps garner support and funding to control it.

NOXIOUS AND INVASIVE PLANT LIST TEXAS DEPARTMENT OF AGRICULTURE

WOODY PLANTS Brazilian peppertree Camelthorn Chinese tallow tree Paperbark Saltcedar Chinaberry Kudzu Tropical soda apple

GRASSES Giant reed Itchgrass Serrated tussock grass Torpedograss

FORBS Broomrape Balloonvine Hedge bindweed Japanese dodder Japanese climbing fern Purple loosestrife

AQUATIC PLANTS Alligatorweed Eurasian watermilfoil Giant duckweed Hydrilla Oxygen weed Salvinia Water spinach Waterhyacinth Rooted waterhyacinth Waterlettuce

The truth is that giant reed has considerable value in protecting creek and riverbanks from erosion and helps capture and stabilize sediment in the floodplain, thus improving water quality. Riparian experts would much rather see a diverse and healthy mix of native species, but where that is lacking, giant reed does an admirable job of stabilizing creek and riverbanks.

The fact is that most invasive species do have certain beneficial values as well as the potential to cause harm. No plant is either completely bad or completely good. All plants, native and non-native, have characteristics that can be both desirable and undesirable.

MANAGE NOT ERADICATE

We will never be able to eradicate or even control many invasive plants to a significant degree. Most invasives are here to stay and the best we can do is to manage them.

Our arsenal to manage invasive plants is similar to what we use to manage native species and includes herbicide, mechanical methods, fire, grazing, and various combinations of these. Managing invasives requires skill and experience since the methods we use to control them sometimes results in spreading them even more. In addition to the traditional methods, invasive plants can sometimes be effectively managed with host-specific insects such as the salt cedar beetle.

There are several basic strategies to manage the spread of invasive plants. The first seems all too obvious, but we can stop planting them.

Some of the grasses that are most detested as invasive are still being actively planted on farms and ranches for their forage value. Some seed companies still market these grasses and some conservation programs share in the cost of planting them. Even if you do not intentionally plant these grasses, be sure to check with your seed company and ask what assurances they can provide that invasive grass seed is not accidentally mixed with native grass seed in small amounts.

Secondly, landowners can limit establishing and spreading invasive species by keeping the land covered with a good, thick growth of native vegetation. Most invasive species find a niche for establishment when there is weak native plant cover or fresh disturbance. The two worst things that invite invasive plants are overgrazing and mechanical soil disturbance.

Many of the initial introductions of invasive species come when heavy equip-

Torpedo grass in foreground along the Pedernales River. Although it is on the invasive species list, torpedo grass helps stabilize riparian areas and reduce erosion.

Photo by Steve Nelle

The old world bluestem in the foreground has been heavily grazed in late summer when Indiangrass (in back) is less palatable.

ment is brought to the ranch to control brush, develop energy or construct roads and right-of-ways. Anytime outside fill material or road base is brought in, there is a good chance of bringing in unwanted plants.

Following such disturbances, pay close attention to new infestations. Invasive plant detection and control provisions can be written into energy production contracts to reduce risk.

The most aggressive way to combat invasive species is to kill them either with herbicide, solarization, repeat plowing, or a combination of these. These are usually not practical or cost effective on a large scale, but can be useful in smaller areas. The main thing to remember is that repeat applications will be needed so be prepared for a long battle and numerous follow-up efforts.

One of the most promising and practical ways to reduce the dominance of certain invasive grasses is the creative use of livestock grazing. For example, K R bluestem is often leafy and palatable in late summer and early fall when the native grasses have become coarse and lignified.

At this time of year, cattle will often walk right past desirable native grasses such as Indiangrass and little bluestem to graze K R bluestem and they will often graze it hard. Another example is using goats to suppress salt cedar seedlings.

For each region there are seasons when each plant is more and less palatable. Astute managers will be observant and make note of when the invasive plants are more palatable than the natives and use that information to practice targeted grazing with cattle, sheep, or goats. This approach will not eliminate invasive plants but it can reduce their dominance and give a benefit to the natives.

Those who most strongly dislike invasive plants are prone to show their hatred by calling them worthless, destructive, insidious, vicious, wicked, nasty, hideous, disgusting, and other names unfit to print. Yes, invasive plants can be a serious concern on farms, ranches, and forest land and sometimes there are reasons to be concerned. But our responses should be based on logic and sound judgement, not animosity.

One thing is certain—most of the species we label as invasive are here to stay and are now a part of our farms, ranches, forests, parks, and yards. Common sense says we should learn to manage them where needed and benefit from them where possible. The stewardship mentality says that we look at the everchanging landscape with a wide-angle lens, trying to understand how all the parts fit together—the original parts as well as those that were recently added.