The South Texas Plains constitute a triangular region, roughly south and east of a line from Del Rio to San Antonio to Rockport. Also called the Rio Grande Plains or south Texas "brush country," the region encompasses about 20.5 million acres, covering fifteen counties in their entirety and portions of fourteen others. Major ranches such as King, Kenedy, Callaghan, Piloncillo, San Pedro, Briscoe, Chittum and Farias are located in the area.
The topography varies from generally level to a gently undulating plain that drains into the Gulf of Mexico by way of the Rio Grande and Nueces rivers and their tributaries. Elevation ranges from sea level along the coast to nearly 1,000 feet in the northwestern portion. Soils are very diverse and range from clays to fine sands and from calcareous to slightly acidic. Since specific soils generally support distinct plant communities, common vegetation communities can generally be characterized on the basis of soil maps. Frequently, certain plant species can be used to identify and describe habitat quality and the wildlife values of a site.
The climate of the area is generally mild with average annual temperatures ranging from 66 to 74 degrees Fahrenheit. Summer temperatures often exceed 100 degrees and severe frosts occasionally occur during the winter. The average growing season lasts 340 to 360 days. Prevailing winds are from the southeast, bringing warm moist air from the Gulf of Mexico. There is a pronounced rainfall gradient across the region, with average rainfall about 33" on the eastern edge and 17" on the western edge. Peak rainfall occurs in May, with a secondary peak in September. Droughts are common and "normal" rainfall is frequently significantly above or below the historical average. Extreme variability in rainfall and hot temperatures are important factors that influence habitats of south Texas.
Spanish explorers who traveled across this region left documentation describing the landscape and vegetation. Contrary to popular belief, the entire area was not a continuous prairie of "stirrup high" grasses. Although grasslands apparently dominated the landscape, woody plants (trees and shrubs) were often present in thickets, upland areas, major drainages and river bottoms. Natural fires helped to maintain the region as a grassland or savannah, and reduced woody plant densities.
Early settlers of the region depended on livestock to make their living. The invention and introduction of barbed wire allowed settlers to fence livestock. Fencing and unrealistic expectations of grazing capacity led to overgrazing. Although the area is historically known for its thriving cattle industry, from the late 1860s to the 1890s sheep played an extremely important role in shaping present-day south Texas. Corpus Christi was the nation's largest export center for wool in 1880. In 1889, four of the top sheep-producing counties in Texas were located within the South Texas Plains.
The sheep industry declined around the turn of the century and cattle have since dominated the livestock industry.
Brush densities increased during the late nineteenth and early twentieth centuries due to a variety of factors, which probably included overgrazing, lack of natural fires, soil compaction and periodic droughts. Originally, increased brush density was regarded as detrimental by ranchers, and attempts to control it were intensive and widespread. The earliest attempts at brush control and range reseeding began during the late 1930s and early 1940s, with cabling and chaining. As ranchers generated income from livestock production, they also practiced rootplowing, roller chopping, Rome discing and chemical spraying to control brush and to increase grass production. Research into the effects of brush management by wildlife biologists in the late 1960s indicated that extensive brush control was detrimental to wildlife. White-tailed deer hunting increased in popularity during the late 1950s, 1960s and 1970s, giving landowners an economic incentive to provide quality habitat for white-tailed deer. Consequently, brush removal has been reduced or applied in a manner that is not detrimental to wildlife, thus improving the habitat for deer and other wildlife species. Research has shown deer prefer forbs; however, woody plants and cacti become an important staple in drought-prone western south Texas. Identification of key food plants then becomes an important aspect of evaluating habitat, range condition and ecosystem health. Additionally, knowing the nutritional value of plants can also help in range analysis.
Protein in an animal's diet is essential for growth, maintenance and reproduction. Crude protein (CP) is an estimate of a plant's protein content expressed as a percentage of the total plant, but is not what is actually available to the animal. Certain plants (e.g. Acacias spp.) have defenses against consumption which include structural deterrents such as thorns and/or chemical weapons. The chemical defenses are secondary compounds which sometimes interfere with digestibility and/or are poisonous to the animal. Digestible protein (DP) is the amount of protein in the plant that is actually digested and utilized by the animal. Digestible dry matter (DMD) is the percentage of ingested food actually absorbed into the animal's system. This percentage includes proteins, along with carbohydrates. These values are found in the nutritional chart provided at the end of this book.
Brush management can affect the nutritional value and chemical composition of plants. Proper brush management can benefit wildlife by improving the nutritional value of plants or by just creating desired habitat, sometimes both. There are many techniques used for manipulating or managing brush densities and diversity, including mechanical and chemical means, as well as fire. Fire or controlled burning is an excellent technique for brush management and extremely beneficial to wildlife. The most limiting factor in south Texas is adequate herbaceous ground cover to fuel the fire. Controlled burning is often used as a follow-up treatment after mechanical or chemical manipulation.
Brush-management patterns such as strips, blocks, zigzags, contours and mosaics are also important. Elaborate patterns are more expensive but are generally more beneficial to wildlife, due to the creation of greater landscape diversity and increased "edge effect." A minimum of 250 yards on either side of creeks and drainages should be left intact to provide travel corridors for wildlife. Brush removal should not exceed 25-30 percent of the overall area. Soil types, topography, vegetation types, climate, clearing patterns, amount of removal and pre-management and post-management usage must all be considered when managing brush. A certain density of brush may provide good habitat for some wildlife species while not for others.
Livestock-management issues, including stocking rates, grazing systems, water availability and supplemental feeding distribution, also affect wildlife habitat. Livestock grazing has a greater effect on wildlife habitat than any other factor in terms of acres impacted. Livestock utilize brush for food and shelter to varying degrees, depending on season and forage availability. Proper stocking rates and grazing systems benefit the producer and the resource. A multi-herd, multi-pasture rotational system ranked high for simultaneous production of livestock, white-tailed deer, bobwhite quail and turkeys in one scientific study. Lower stocking rates increase ground cover for ground-nesting birds and mammals, by decreasing potential nest destruction and predation. Additionally, adequate ground cover lowers ground temperatures and increases humidity, providing for better productivity of ground-nesting vertebrates such as quail, turkeys and tortoises.
(calico bush, bunchberry, mejorana, hierba de cristo, monte cristo)
A deciduous, wide-spreading, aromatic perennial shrub (1'-6') with multiple upright, green-to-reddish, rough and somewhat prickly stems. The younger stems are somewhat squarish. The simple, opposite, aromatic, hairy leaves have dark green upper sides and light green undersides, and serrated edges. The showy flowers are clumped into rounded heads and vary in color between red, orange and yellow. The flowers are produced throughout the summer from the upper leaf axil. The fruit is a small, dark blue or black drupe, ripening on long peduncles (1"-4") from August to September.
Lantana is a common plant usually found in all types of habitats, but it prefers sandy and gravelly soils and hot, dry areas. It is frequently found in mixed-brush communities, and in fallow fields, along roadsides and in fence rows.
Lantana is reportedly toxic, with little browse value for wildlife, although some birds, including quail, eat the fruit. Small mammals and reptiles occasionally use the plant for cover. It is a food plant for butterfly larvae and a source of nectar for adult butterflies.
It is also toxic to livestock and humans.
Lantana is an attractive, low-spreading ornamental and landscaping plant. In Mexico, crushed leaves were reportedly used medicinally to treat stomach ailments and snake bites.