Release Date: June 19, 2001
Mesquite Becoming Thorny Water Issue for All of Texas
For more than half a century mesquite has been a thorny problem for ranchers, but as Texas moves deeper into the 21st century urban dwellers have reason to be concerned about the thirsty plant that is the scourge of rangelands.
The more that mesquite plants drink, the less water that makes it into the state's reservoirs and aquifers, said Cody Scott, Ph.D., of the Angelo State University Agriculture Department. Ultimately, that means trouble for all of Texas.
"Current water use in Texas exceeds the rate at which we replenish our water supply," Scott said. "Thus, effective mesquite control is becoming even more essential if we are to guarantee an adequate water supply for Texas' growing population."
Consequently, the state's urban and non-agricultural populations have a stake in the battle against mesquite, which has proven itself adaptable and durable on rangelands throughout central and western Texas. A study of the North Concho River watershed two years ago indicated that the estimated 130 million mesquite trees and 100 million juniper trees in the watershed were consuming almost 2 million acre feet of water annually. By contrast, the City of San Angelo was consuming approximately 20,000 acre feet a year. An acre foot of water is the equivalent of 325,850 gallons.
Annually, Texas ranchers spend millions of dollars on mesquite control but there is no long-term answer in sight to counter the durable and pesky plant. In the 1950s, Scott said the goal was to eradicate the mesquite. Eradication, Scott said, was unattainable and the emphasis from the 1960s through the 1980s changed to managing the spread and density of the brush. Despite the high cost, mesquite control is essential for ranchers to maintain profitable livestock operations, to provide wildlife habitat and to sustain water for agricultural and human use.
Scott said mesquite harms the land by crowding out native bunchgrasses which provide forage for livestock, habitat for quail and ground-nesting birds, and erosion control and by transpiring vast amounts of water.
"Mesquite trees are especially durable," Scott said, "because they have both a deep taproot to reach underground moisture and an advantageous root system just below the soil surface to capture moisture from even the smallest rainfalls. Once a mesquite seed germinates, it quickly roots down to capture underground moisture. It can establish on a wide variety of soil types and can withstand drought conditions."
On top of that, mesquite trees are long-lived plants while most grasses only survive for a few decades. Once grass stands die, mesquite moves in and, given its longevity, can remain the dominant plant for many decades.
Besides that, mesquite has no natural mechanism to control its spread. To the contrary, it seems designed even destined to proliferate. First, it contains toxins that prevent most animals from consuming the plant itself. Though a few insects will feed on mesquite foliage, they seem to have little impact on the plant.
Further, mesquite is a prolific seed producer and those seeds, unlike the plant itself, are edible. Both livestock and wildlife are known to eat the seeds, Scott said. The problem is that the seeds are not easily digestible and many of them survive in the manure.
"Given the large concentration of livestock and the diversity of wildlife species in central and western Texas," Scott said, "mesquite seeds are deposited in manure an ideal microsite for seedling germination and establishment and are quickly dispersed across the landscape, making mesquite control even more of a challenge for ranchers."
In addition to cattle, sheep and goats, Scott said several species of wildlife eat mesquite beans, including deer, raccoons, opossums, foxes, coyotes, skunks and several rodent species. The wildlife consumption helps explain why mesquite often winds up in Conservation Reserve Program (CRP) fields ungrazed by livestock.
Scott said that while cattle, sheep and goats all consume mesquite beans, particularly when the seeds have reached maturity, goats are the most efficient at digesting the seeds. They not only consume a large number of seeds given their body size, but they also spread fewer viable seeds through their droppings than do cattle and sheep.
Additionally, goats like sheep, but unlike cattle will consume immature mesquite seedpods, he said. When this occurs, the seeds are destroyed before they are fully developed. If ranchers could avoid grazing some pastures after mesquite beans reach maturity, they could reduce the number of number of viable seeds dispersed across the landscape.
"The fact that goats are better able to destroy mesquite seeds through digestion and the fact that they will consume immature seeds is very encouraging," Scott said.
Some research with poisonous plants has shown that animals can be trained to avoid certain plants when they are fed a non-toxic level of the plant and then given a mild toxin that causes nausea. The animal associates the nausea with the taste and refuses to eat the plant thereafter, he said. A similar approach with mature mesquite seeds may offer some hope to reduce livestock spread of mesquite. Combining this approach with goat grazing when immature seeds are available could reduce the viable seeds dispersed across the landscape. Long-term control, though, is difficult given the prolific seed production and high rate of seedling establishment.
If seed production and subsequent dispersal could be limited, the duration of mesquite control could be dramatically increased when combined with hand-spraying after intensive brush control efforts.
"The result," Scott said, "could be savings in costs to ranchers and in water to everyone."