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Historical Vegetation Changes on The Edwards Plateau of Texas and the Effects Upon Watersheds

by Mike Mecke

Former San Antonio Water System Employee

and Former Vice President, Bexar Audubon Society

SPANISH EXPLORATIONS - 1675 TO 1723

The early Spanish explorers of the Southwest were required by the Spanish Crown to keep diaries of their travels (1.) Many had more than one diarist accompanying their expeditions to record "the leagues traveled, the mountains, streams, prairies, and woodlands crossed, and the chief characteristics of these natural features of the land (2.)" Fortunately for historians and others interested in the early history, geography and natural history of Texas many of these early explorers accurately described the vegetation and wildlife which was found in Texas during early Spanish colonial times.

The first European explorers of Mexico and Texas came themselves from the high arid plains of Spain where water was more precious than gold." (4.) Texas was mapped in 1519 by Capt. Alonso Alvarez de Pineda and one of his unnamed rivers was the San Antonio River. It is unsure as to which Spaniard first camped at the headwaters of the river at the San Antonio springs. Many historians believe that Cabeza de Vaca was the first in the 1520's when he wrote of his shipwrecked adventures and first described the buffalo in writing. Other historians credit Alonso de Leon as the first in 1670. In 1691 the first governor of Texas, Domingo Teran de Los Rios and Fray Damian Massanet, a Franciscan missionary, camped at or near the present day San Antonio springs alongside a village of friendly Indians. Some authors interpret Massanet's diary to actually describe Leon Springs as what he named "San Antonio de Padua" whereas others are sure that they first camped at San Pedro Springs, which are much nearer to the river's headwaters (1.) The flag of Spain was raised and the expedition marched eastward on "The King's Road" to the boundary of French Louisiana to expel all foreigners and lay claim to the lands for the King of Spain (3.)

Thus, San Antonio with its clear, cool, flowing springs and lush river became the most important stopping point for all future expeditions. Spanish expeditions began from various points, but most eventually travelled to San Antonio, known in early days as San Antonio de Bexar. In 1718, nine years after his quest for the establishment of a mission in San Antonio, Father Antonio de Olivares, broke ground for mission San Antonio de Valero. Days later Governor Alarcon of the Province of Tejas founded the Presidio de Bejar (Bexar) and its Villa (3.) The first Mission San Antonio was located west of San Pedro Springs, which forms a tributary of the San Antonio River. A year later the mission was moved to a site near its present location, where it remained until destroyed by hurricane floods in 1724 and then moved to its final location on Alamo Plaza. In 1801 the mission was renamed "Alamo" after a Spanish cavalry company from the town of Alamo (which meanscottonwood) in Mexico (3.)

Manzannet, diarist on the Teran expedition, described the area explored as very beautiful, having hills with large oaks and easy for travel. He describes a region well-grassed with few oaks and mesquites on the hills and along streams. There were many fish in the streams, chickens (prairie) on the highlands and buffaloes roamed the region (1.)The Espinosa-Olivaris-Aguirre expedition of 1709 traveled into the present Bexar County through a well-watered route with only the arroyos and creeks being timbered with oaks, mesquites, walnuts, poplars, elms and mulberries (1.)Espinosa reports on the Ramon expedition of 1716, of travel through hills and dales covered with lush pasturage of very green grama-grass. Only sparse mesquites and some oaks were reported until reaching the various springs, creeks and rivers near San Antonio (1.)The Aguayo Expedition of 1720, as reported by Pena, also rode across a " beautiful treeless plain with fertile valleys until reaching San Antonio." Leaving Bexar in 1722, Aguayo traveled thru "a beautiful level country sparsely covered with evergreen oaks." (1.)

THE EDWARDS PLATEAU REGION OF TEXAS

The Edwards Plateau region of central and west-central Texas is locally known as "the Hill Country." It is bounded on the east and on the south by the Balcones Fault, which caused a geological uplift known as the Balcones Escarpment. The Plateau's northern edge grades into the Cross Timbers Oak, the Llano Uplift and the north Plains Regions. On the west, the Plateau is bounded by the Rio Grande and the Pecos Rivers. The Edwards Plateau consists of 31,000 square miles and ranges in elevation from 1000' msl to over 3,000'msl. Precipitation is near 33 inches at Austin in the east down to 15 inches along the Pecos River in the west (4.)

The Plateau is composed of Edwards and Glen Rose limestones with large areas exposed at the surface of this predominantly rangeland region. The shallow calcareous soils are dissected by many canyons along the southern boundary with steep grades and exposed geological strata. Several river systems flow from the region with the Nueces, San Antonio and Guadalupe River basins being the most important. The well known Edwards Aquifer is fed by precipitation and streamflow from the 4,400 square mile Drainage Area which is in 13 counties lying north of the Edwards Recharge Zone (ERZ). (See map)

Water entering from the ERZ percolates by gravity through the exposed limestone fractures and pore spaces into the aquifer flowing generally to the southeast. Aquifer flows are from areas where the water levels are at higher elevations to areas where the water levels are at lower elevations (near the major springs.) Caves and sinkholes are very common in this area. The complex geology of the aquifer has produced estimated flow rates ranging from two to 31 feet per day, but local transmission rates of as much as 1,000 feet per day have been recorded.

In the Artesian or Reservoir Area of the aquifer, the Edwards limestone is buried between confining formations. The Edwards formation is about 500' thick in this area and slopes downward to about 1000' below the land surface at the southern edge of this zone. The Edwards Aquifer contains many pore spaces and huge underground pools which have often produced wells from 6000 to 7000 gals/min. The highly controversial Living Waters Catfish Farm's artesian well produced about 40 million gallons per day during its brief existance. 

Prior to well drilling and pumping, there existed a natural balance in the aquifer between recharge and spring flow. Of the five major springs in the region: the Leona (in Uvalde), San Antonio and SanPedro (in San Antonio), Comal (in New Braunfels) and San Marcos, only the later two are now of any significance. Many small springs in the region are now dry or only flow during very wet years (5.) Many of the formerly perennial Edwards Plateau creeks now only flow intermittently.

EARLY VEGETATION OF THE EDWARDS PLATEAU

Some of the common grasses first identified on the Plateau's upland sites were little and big bluestem, Indiangrass, sideoats grama, Canada wildrye, Texas wintergrass, buffalograss, etc. Riparian area grasses included switchgrass, eastern gamagrass, Virginia wildrye, and a mix of dropseeds and the smaller bluestems. The drier western section of the Edwards commonly grew shorter grasses such as: tabossa, curly mesquite, various threeawns, and several grama grasses. Mixed with these prairie grasses were forbs such as: western indigo, Englemann- daisy, Maximilian sunflower, velvet bundleflower, western ragweed, broomweed, sneezeweed, salvias, Indian paintbrush, bluebonnets, coneflowers and sensitive-briar (6,9.)

Trees and shrubs found on the Plateau included: many oaks such as live oak, Spanish, burr, shin, blackjack and post oaks; hackberrys and elm; mesquite; junipers ("cedars" - two species), catclaw, yucca, cacti, bumelia, cenizia, mountain laurel and sumacs. The cooler and more moist bottomlands and canyons also contained many eastern species mixed with western plants. Found in these less xeric environments were: pecan, ash, bald cypress, walnut, mulberry, maple, willow, sycamore, cottonwood, grapevine, and green briar (7,8.)

In scattered sites across the region were found less common plants such as: Texas madrone, hickory and even pinyon pine on many southwestern hill tops. The drier and hotter western Edwards Plateau was home to numerous genera of cacti including: tasajillo and cholla, plus other shrubs including ocotillo, saltbush, snakeweeds, acacias, prunus, sacahuista, ephedras, lechuguilla and agarita (9.)

THE VEGETATION CHANGES — CAUSES & RESULTS

By 1930, heavy, continuous grazing combined with range fencing and the control of wildfire, greatly reduced growth of the more desirable grasses allowing many shrubs and trees to invade the uplands. What early Texas explorers once had described as "a waving sea of grass, often stirrup-high on a horse or high as a cow's back" deteriorated into the present shortgrass, rock, shrub, cactus and tree dominated landscape. (10) Soil conservation experts estimate that between 1930 and 1995, many tons per acre of valuable top soil have been lost, especially from the steeper and more shallow soiled hillsides and from overgrazed riparian areas. We know from rancher's quotes, historical records and maps that many springs have dried up, numerous perennial creeks now only flow intermittently and grassland productivity has been drastically lowered. Ranges which once supported from 300-500 cattle per section (640 acres) in the 1860's often are presently recommended by range managers to carry no more than 50 animal units per section.

As the more palatable grasses and forbs decreased or even disappeared, many ranchers on the Plateau switched to cattle, sheep and Angora goat operations, often grazing all three types of livestock to better utilize the now dominant shrubby vegetation (6.) Unfortunately, little attention was given, and less was known until decades later, concerning desirable proportions of each type of livestock pastured together.This factor, combined with the steady climb of deer herd numbers on the Edwards Plateau has caused further range deterioration on much of the region. Wildlife and range managers have credited the tremendous increase in deer numbers on the Plateau to several factors. Competent range and wildlife management is now often complicated by free-ranging herds of exotic big game animals, which are commonly found across much of the Edwards Plateau. Many ranches contain several species of exotics - either contained within game fences or free-ranging. Several exotics directly compete with native wildlife and/or livestock (11.)

On the Plateau the most prominent and widespread brush invaders are junipers, primarily ashe juniper; liveoak, mesquite, shinoak, and cactus. Ashe juniper, also called blueberry cedar or mountain cedar, is by far the most common shrub invading the southern and central Edwards Plateau. Cedar, a water hog, may become dominant, but is very susceptible to killing and long-term control by fire (12, 13, 16.)

Prior to the brush invasion, dense mid and tallgrass stands slowed runoff, organic matter in the soil enhanced water infiltration allowing rains to rapidly replenish not only the Edwards Aquifer, but other local aquifers as well. Today, runoff erodes bare areas beneath and around cedars, woody biomass intercepts moisture, while also dominating the grasses and forbs for space, sunlight and soil nutrients. Many of these evergreen woody plants transpire water year-around, which further increases soil water losses.

The most valuable product of rangelands is water!! Ideally, rangelands should be managed not only to provide livestock forage, wildlife habitat, and recreational opportunities - but, primarily, to produce sufficient quantities of clean water throughout watersheds. This water maintains creek and river flows and recharges aquifers. If watersheds become infested with heavy water utilizing shrubs and trees, they soon lose the beneficial characteristics so desired by hydrologists (15.)

One of the principal net effects of this woody plant invasion coupled with the decrease in herbaceous vegetation, is that less water is available to replenish the Edwards Aquifer - especially during dry years, when little rain runoff is available for groundwater recharge. This is the effect which should be of most concern to not only to the urban users and industry, but also to irrigators, ranchers, wildlife biologists, downstream water users and to the federal courts which are now protecting the Endangered Species in the Comal and San Marcos Springs. Recent Texas research has shown water savings varying from 30,000 to 160,000 gals/acre/yr. resulting from differing levels of ashejuniper control. Complicating the serious present concerns about the Edwards Aquifer's quality and quantity of water, are the Texas Water Development Board's 1990 projections for state municipal and industrial water demands to increase by 186 % by the year 2040.

SUMMARY

— Site hydrology greatly affected by vegetation changes

— Juniper significantly reduces amount and distribution of water reaching the soil

— Juniper out competes herbaceous plants, potentially uses more water

— Combined effects of juniper invasion on rangelands is reduced water yields and herbaceous plant production, plus wildlife habitat losses

REFERENCES

1. Inglis, Jack M., 1964. A History of Vegetation on the Rio Grande Plain. Bul. 45. Texas Parks & Wildlife Department.

2. Hoffman, F.L. 1935. Diary of the Alarcon Expedition into Texas, 1718-1719, by Fray Francisco Celiz. Quivara Society, Pub.V.

3. Guerra, Mary Ann Noonan. 1987. The San Antonio River. Alamo Press.

4. Godfrey, Curtis L., Clarence R. Carter and Gordon S. McKee. Land Resource Areas of Texas. Undated. Pub. 1070. Texas A & M University.

5. Powers, Chris. (Editor) 1993. The Case for New Legislation for the Edwards Aquifer. San Antonio Water System.

6. Buechner, H.K. 1944. The Range Vegetation of Kerr County, in Relation to Livestock and White-tailed Deer. American Midland Naturalist.

7. Bray, W.L. 1904. The Timber of the Edwards Plateau of Texas. USDA Forest Service Bulletin 49.

8. Palmer, Ernest J. 1920. The Canyon Flora of the Edwards Plateau of Texas. Journal of the Arnold Arboretum 1: 233-239.

9. Bray, W.L. 1901. Ecological Relations of the Vegetation of Western Texas. Botanical Gazette.

10. Bentley, H.L. 1898. Cattle Ranges of the Southwest. Bul. 72, USDA.

11. Mecke, Mike. 1978. Texotics - Exotic Ungulates in Texas. Unpublished Graduate Paper, University of Wyoming.

12. Taylor, Charles & Others. 1994. Juniper Symposium. Tech. Rpt. 94-2,Texas A & M University Research Station at Sonora.

13. Mecke, Mike. 1963. A Discussion of the Burning of Slash in Ashe Juniper Woodlands. Unpublished Graduate Paper. Texas A & M University.

14. McCarl, Bruce A. & Others. 1987. Brushland Management for Water Yield: Prospects for Texas. Bul. B-1569, Texas Ag. Expt. Station

15. Richardson, C.W. & Others. 1979. Hydrologic Effects of Brush Control on Texas Rangelands. Transactions of the ASCE, Vol. 22, No.2.

16. Brand, Rex & Joe Franklin. 1991. Cattle and Fire - Important Tools Benefiting Wildlife. Rangelands, 13 (4).

16. USDA - Natural Resources Conservation Service, Texas A & M U. and Texas State Soil & Water Conservation Board. 1995. Water Conservation for the Edwards Aquifer.

PRESENT RESEARCH SITUATION

On several small watersheds near Sonora (Edwards Aquifer Drainage Area) and Uvalde (Edwards Aquifer Recharge Zone/ERZ) both the Texas A & M University System and the USDA - Natural Resource Conservation Service (NRCS) personnel have effectively demonstrated the positive impact of brush management and grazing management on both water quality and quantity. As the studies were conducted on small areas (5 to 20 acres), some observers are not convinced that the results are applicable on large land tracts elsewhere on the Edwards Plateau.

Similar results have been obtained across Texas and the rest of the Southwest, treating juniper, mesquite and other brush species, in both USDA and privately financed range management programs.

But, unfortunately, there is little information in the research database to provide convincing evidence of the hydrologic values of various brush control and grazing management practices, especially those combined with the use of prescribed fire on cedar on the southern Edwards Plateau.

RESEARCH PROPOSAL OUTLINE

The USDA - NRCS and the Texas A & M University System are proposing long-term, ranch scale experiments to restore and maintain savannah grassland biodiversity and productivity with prescribed burning. Tentatively, large ranches are sought in Bexar, Medina and Uvalde Counties for the project.

Three ERZ area ranches will receive a variety of treatments including: chaining, selective tree-dozing, prescribed burning, "goating", reseeding and grazing system management. On each ranch, treated areas of several thousand acres will be subjected to a selection of treatment combinations and then compared to similar untreated pastures.

Reseeded pastures will be planted to native and adapted perennial mid-and tall-grass species. Native forbs will be included to improve biodiversity, wildlife habitat and livestock forage quality.

Wildlife management experts will assist in planning and conducting research operations in a manner compatible with both game and non-game habitat needs. Deer herd (or exotics, if present) management will be directed by Texas Parks & Wild-life Department (TPWD) biologists. Project plans will be approved by US Fish & Wildlife Service and TPWD biologists to assure agreement with Endangered Species regulations. Most woody vegetation along drainage areas, in shallow soil areas and on other important wildlife sites, will be left untreated as essential wildlife habitat.

In most cases, important wildlife cover and forage plant species will be protected from any damaging treatments in order to provide the desired mosaic vegetational pattern.

RESEARCH DESIGN

Some treated pastures will receive long-term follow-up brush management consisting of prescribed burning and others will not. Summer vs. winter burns may be a consideration also to determine influence upon vegetative composition, especially perennial grasses. Newer electric fencing types should also be used, not only to reduce costs, but to demonstrate to the public their effectiveness under all types of livestock and grazing systems. Innovative livestock and wildlife water developments such as solar pumps and catchment systems should be considered likewise to demonstrate their competentence to resource managers. If noxious weeds (exotic/perennials) are present in sufficient areas, an integrated management system utilizing biological controls might also be demonstrated.

Research areas will be managed possibly by using some or all of the following suggested strategies (yet to be determined):

(1) no grazing, with burning every four/five years (a possible park-type management strategy);

(2) continuous grazing (cattle) and no burning;

(3) continuous grazing (cattle, sheep and goats) no fire;

(4) continuous grazing (cattle, sheep and goats) chained and burned periodically;

(5) a multi-pasture (HILF-type) one herd rotation with one or more pastures burned each year;

(6) a unit receiving mechanical brush treatment (chaining), with a HILF grazing system, no fire - but flash grazing with goats to manage cedar seedlings;

(7) a multi-pasture, HILF-type system, chained and burned;

(8) a Merrill four-pasture, three herd system (cattle, sheep and goats) where one pasture is burned each year;

(9) a typical pasture, left untreated and ungrazed;

(10) other treatment combinations as determined.

Prior range research has proven that certain livestock ratios combined with grazing systems and brush management can be used not only to increase rancher's profits, but to manipulate ground cover and vegetative composition.

On each research ranch and upon key drainages upstream and downstream, water sampling and gaging sites together with test wells will be strategically located to measure impacts on water quality, quantity (watershed yields) and aquifer recharge. Water losses which occur via plant transpiration will likewise be compared.

Livestock performance will be closely monitored, along with vegetational changes, soil losses and the impacts and effects upon many representative wildlife species.

Effective cedar control and management is expected under several of the proposed treatments, especially those utilizing fire. As a secondary benefit, population reductions should occur, both of cacti and small or seedling mesquites on the prescribed burn sites.

The economic analyses made should provide a practical financial decision-making tool from which users may apply the scientific information derived from this project. Computer models will be developed to identify watershed site predictors which would prioritize future brush management options by predicting water yields and any quality factors.