Invasive grass a problem for native wildlife

A monoculture of exotic invasive grass taking over part of the Laguna Atascosa National Wildlife Refuge, thus destroying the habitat of the endangered ocelot.

 

Anyone who has been reading my column for very long probably already knows I have a real problem with exotics. Previously, on a trip to the Texas Coast and South Texas, I saw, again, the problems presented by many invasive plant species. 

Most people in the Edwards Plateau, and most of the rest of Texas for that matter, are aware of the exotic, invasive grass King Ranch or KR Bluestem, and it is a problem most all landowners have to deal with or just live with.

But in South Texas, two other non-native, invasive grasses — buffelgrass and Guinea grass — are taking over vast areas and completely crowding out native grasses and forbs. In many affected areas, these grasses have formed a tangled, 2-foot-high monoculture of grass with larger shrubs being the only other vegetation. 

These areas are useful habitat for very few species of birds, mammals or animals. 

These grasses were introduced into this country in the apparent belief that they were better forage producers than native grasses. Whether that is true is debatable, but the fact that we found these infested areas in National Wildlife Refuges and an Audubon Nature Center, not to mention along roadsides for miles, is a problem.

People often point out, correctly, that most of the food we eat is in fact not native to North America. All of our livestock (cattle, sheep, goats, pigs and chickens) was introduced by early settlers; none are native to the Western Hemisphere. The same is true with most of our vegetable crops, fruit trees and most all cereal grains (wheat, oats, barley).

So, it is logical to ask, if all of these food-producing species are OK, why isn’t every other newly introduced species? The answer is simple: All of the animals listed above are domesticated; they can be herded, moved, managed, handled, kept in a given area, and their population can be controlled by man. All of the vegetables, fruits and grains can likewise be controlled and don’t spread uncontrolled.

For an exotic plant or animal to become a serious problem, three things have to happen. First, the plant or animal must be able to reproduce without man’s help and/or in spite of man’s attempt to control it. Second, the plant or animal must be able to escape wherever it was introduced and colonize other properties or areas. And third, it must be able to out-compete native species in a way that alters the native habitat.

The majority of introduced species — plant and animal — do not fit those characteristics, but many do, and we don’t know enough to be able to predict in advance which species will become a problem. 

Exotic ungulates (axis, fallow, sika deer, blackbuck antelope) are not much different from goats, so why are they a problem? If one of these exotic species were introduced into a ranch to replace cattle or sheep or goats, and if they never escaped from that ranch, and if their populations were controlled so they did not outcompete white-tailed deer for food, then they could be considered just another livestock species. But these are big “IFs.”

But when axis deer escape and become feral, as feral hogs did many years ago, they are no longer under the control of man. Their population can increase above the numbers the habitat can handle, and then we have a problem.

When a rancher plants a non-native forage grass that can then escape his property and invade other properties, including National Wildlife Refuges, and that grass crowds out native grasses and forbs to the detriment of wildlife, we have a problem.

Some of you may be asking yourselves, don’t white-tailed deer and cedar fit the three criteria I listed above for an invasive species? The answer is that yes, they do. But the reason they do is not because they were introduced from another ecosystem, but that man altered our ecosystem and habitat, to allow deer and cedar to increase in numbers to the point of being invasive. 

We killed most all of the large predators, removing population control of the deer. And we eliminated or stopped most prairie fires, which had previously controlled the numbers of cedar. So we created those problems and we have to fix them.

We didn’t introduce white-tailed deer or cedar into our habitat, but we did introduce KR bluestem, buffelgrass, Guinea grass, Chinaberry, ligustrum, axis, feral hogs and the list goes on and on. 

We have enough problems with invasive exotics already, let’s not introduce any new ones.

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.

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