Physiographic features

This is an upland site. Slope gradients are mainly 1 to 8 percent but can range up to 12 percent. Slopes exceeding 12 percent are classified as Steep Rocky. The very shallow to shallow, well-drained, moderately slow permeability soils of this site were formed in residuum over interbedded limestone, marls, and chalk. The site will receive runoff from the associated Steep Rocky Ecological Site.

Table 2. Representative physiographic features

Table 3. Representative physiographic features (actual ranges)

Climatic features

The climate is humid subtropical and is characterized by hot summers and relatively mild winters. The average first frost should occur around November 15 and the last freeze of the season should occur around March 19.

The average relative humidity in mid-afternoon is about 50 percent. Humidity is higher at night, and the average at dawn is about 80 percent. The sun shines 70 percent of the time possible during the summer and 50 percent in winter. The prevailing wind direction is southeast.

Drought is calculated as 75% below average rainfall. It should be noted that timing of rainfall may be more significant than average rainfall.

Approximately two-thirds of annual rainfall occurs during the April to September period. Rainfall during this period generally falls during thunderstorms, and fairly large amount of rain may fall in a short time. Hurricanes provide another source of extremely high rains in a short time. A review of the rainfall records suggest that rainfall is below “normal” at least 60 percent of the time. Therefore, the erratic nature of the rainfall should be considered when developing any land management plans.

The impact of droughts in the Edwards Plateau cannot be under-estimated. Not only are droughts devastating to the land but also to those that manage the land. Droughts occur roughly every 20 years but not always. A severe drought in 2012 coupled with extreme heat resulted in a die off of juniper over millions of acres as well as other native plants.

Table 4. Representative climatic features

Climate stations used

• (1) MEDINA 1NE [USC00415742], Medina, TX

• (2) SAN ANTONIO/SEAWORLD [USC00418169], San Antonio, TX

• (3) KERRVILLE 3 NNE [USC00414782], Kerrville, TX

• (4) BLANCO [USC00410832], Blanco, TX

• (5) CANYON DAM [USC00411429], Canyon Lake, TX

• (6) BURNET MUNI AP [USW00003999], Burnet, TX

• (7) AUSTIN GREAT HILLS [USC00410433], Austin, TX

• (8) GEORGETOWN LAKE [USC00413507], Georgetown, TX

• (9) PRADE RCH [USC00417232], Leakey, TX

Influencing water features

This being an upland site, it is not influenced by water from a wetland or stream.

Wetland description

N/A

Soil features

In a representative profile for the Low Stony Hill ecological site, these soils are very shallow or shallow to indurated limestone. Depth of bedrock ranges from 4 to 20 inches. The soil is a black clayey soil and is neutral to alkaline. Subrounded to angular gravels, cobbles, and stones of limestone comprise 35 to 70 percent by volume of the soil. Surface fragments reduce surface evaporation and help protect palatable grasses and forbs from overuse. The soils are fertile, usually have good structure, and take in water readily. Their fertility and moisture-holding capacity, however, is limited by soil depth and fragment volume. Fractures in the limestone bedrock, on the other hand, generally contain fine soil particles and store moisture. Plant roots penetrate these cracks and crevices, and thus have access to more moisture and plant nutrients than is apparent in the soil. Forage produced on the site is of good quality. These sites occur on interfluves and sideslopes of ridges on dissected plateaus.

Due to the scale of mapping, there are inclusions of minor components of other soils within these mapping units. Before performing any inventories, conduct a field evaluation to ensure the soils are correct for the site.

The representative soil series associated with the Low Stony Hill ecological site is Eckrant.

Table 5. Representative soil features

Animal community

This site is used for the production of domestic livestock and to provide habitat for native wildlife and certain species of exotic wildlife. The site is somewhat accessible to use by cattle but is more accessible to deer, sheep, Angora goats, and meat goats. Global Positioning Systems studies reveal slopes above 11 percent are generally less accessible to cattle while sheep and goats can utilize slopes up to 45 percent. Also revealed is that cattle will avoid a site once it contains about 30 percent surface rocks. (Hanselka, et al.)

Cow-calf operations are the primary livestock enterprise although stocker cattle are also grazed. Sheep and goats were formerly raised in large numbers and are still present in reduced numbers. Carrying capacity has declined drastically over the past 100 years because of the deterioration of the reference plant community. A field assessment of vegetation is needed to determine stocking rates based on the forage needs of desired animal species.

Many species, including domestic livestock, use more than one ecological site to meet their habitat needs.

Managing all the grazing/browsing animals is important to keep populations in balance and provide an economically important ranching enterprise. Achieving a balance between woodland and more open plant communities on this site is an important key to deer management. Competition among deer, sheep, and goats is an important consideration in livestock and wildlife management and can cause damage to preferred vegetation.

Smaller mammals include many kinds of rodents, jackrabbit, cottontail rabbit, raccoon, skunks, opossum, and armadillo. Mammalian predators include coyote, red fox, gray fox, bobcat, and mountain lion. Many species of snakes and lizards are native to the site.

Many species of birds are found on this site including game birds, songbirds, and birds of prey. Major game birds that are economically important are Rio Grande turkey, bobwhite quail, and mourning dove. Turkey prefers plant communities with substantial amounts of shrubs and trees interspersed with grassland. Quail prefer plant communities with a combination of low shrubs, bunch grass, bare ground, and low successional forbs. The different species of songbirds vary in their habitat preferences. In general, a habitat that provides a large variety of grasses, forbs, shrubs, vines, and trees and a complex of grassland, savannah, shrubland, and woodland will support a good variety and abundance of songbirds. Prairie chickens (Tympanuchus spp.) were also noted in the general area. Birds of prey are important to keep the numbers of rodents, rabbits, and snakes in balance. The different plant communities of the site will sustain different species of raptors.

Various kinds of exotic wildlife have been introduced on the site including axis, sika, fallow and red deer, aoudad sheep, and blackbuck antelope. Their numbers should be managed in the same manner as livestock and white-tailed deer to prevent damage to the plant community. This is especially true for exotics such as axis deer which have the ability to switch their diet readily among different plant types rendering them highly competitive for the native white-tailed deer. Feral hogs are present and can cause damage when their numbers are not managed.

Plant Preference by Animal Kind:
This rating system provides general guidance as to animal forage preference for plant species. It also indicates possible competition and diet overlap between kinds of herbivores. Grazing preference changes from time to time, especially between seasons, and between animal kinds and classes. An animal’s preference or avoidance of certain plants is learned over time through grazing experience and maternal learning (http://extension.usu.edu/behave/Grazing). Preference does not necessarily reflect the ecological status of the plant within the plant community. For wildlife, plant preferences for food are rated. Refer to detailed habitat guides for a more complete description of a species habitat needs.

Legend
Rating Preference Description
P Preferred Percentage of plant in animal diet is greater than it occurs on the land
D Desirable Percentage of plant in animal diet similar to the percentage composition on the land
U Undesirable Percentage of plant in animal diet is less than it occurs on the land
N Not Consumed Plant would not be eaten under normal conditions. It is only consumed when other forages are not available
T Toxic Rare occurrence in diet and, if consumed in any tangible amounts results in death or severe illness in animal
X Used Degree of utilization unknown

Hydrological functions

The existing plant community with representative plant species, current soil conditions (soil health), current management, and climate determine the dynamics of the water cycle on this site. Plant and litter cover are important factors which protect the site from erosion; however, total production and particularly the types of plant species present have a greater impact on hydrologic dynamics infiltration capacity, runoff, and soil losses). For example, foliar cover values could be similar among the various states as depicted in the state and transition diagram; however, hydrology (infiltration capacity, water holding capacity, and runoff) will be different. The common denominator is not cover: the most important factors are the types of plants and their abundance on the site. Plant biomass of the desirable native grasses is the most important variable that is correlated with the hydrologic function on this site. Another important factor is the structure and morphology of the root system associated with plant species. Soil factors most associated with high hydrologic function are organic matter content, non-compacted soil surface (lower bulk density), intact soil structure, high porosity, high aggregate stability, and the presence of soil biotic factors, such as earthworms, fungi, blue-green algae, and mosses (when moist).

As the site becomes dominated by woody species, especially oaks and juniper, the water cycle altered. Interception of rainfall by tree canopies is increased which reduces the amount of rainfall reaching the surface. Stem flow is increased because of the funneling effect along the stems which increases soil moisture at the base of the tree. Increased transpiration, especially when evergreen species such as live oak and juniper dominate, provides less chance for deep percolation into aquifers. As woody species increase, grass cover declines, which causes some of the same results as heavy grazing, higher runoff, and erosion. Brush management combined with good grazing management can help restore the natural hydrology of the site.

The soils on this site are well drained with very low water holding capacity. Surface runoff can be rapid because of the slope and physiography of the site. Soils correlated with this site are in Hydrologic Groups C and D.

State 1: Savannah State
With reference to the transitional pathway diagram, the open grassland with oak mottes is associated with the maximum hydrologic function. The high degree of hydrologic function in State 1 is because of the dominance of rhizomatous tall and mid grasses (see narrative). As explained above, when properly managed, these species provide adequate cover. However, one of the keys to high hydrologic function is the structure or morphology of the root system. During high rainfall periods, water will percolate beyond the immediate surface root zone via fractures in the soil strata. As this water moves downward, it contributes to the recharge of aquifers if the underlying soils and geology are appropriate. When conditions are representative of the high composition of tall and midgrass species, little runoff occurs.

The reference plant community is dominated by tall bunchgrass species that are correlated with high hydrologic function. When conditions degrade, into states 2 and 3, the composition of desirable tall grasses decreases and mid and short grasses become more dominant. If soil conditions also degrade and management is consistent with overuse, hydrologic function decreases significantly.

The Grassland Savannah Community of State 1 features little bluestem as the dominant native grass species. The root system of little bluestem consists of a vast network of roots and masses of finely branched rootlets, some more than 30 inches in length. The largest roots are about 0.5 to 1mm in diameter. The soil beneath the grass crown and several inches to the sides are threaded with dense mats of roots to a depth of 4 to 5 feet. Stem bases and surface roots bind the soil in and around the plant bunches—most of the space between bunches is occupied by a dense network of roots. Litter cover accumulating during the winter months can provide protection from raindrop impact. Infiltration studies have shown that bluestem, Indiangrass, and sideoats grama are associated with higher infiltration capacity compared to other short-statured grasses which tend to have thicker fibrous surface roots (e.g., gramas, buffalograss, dropseeds, threeawn grasses). The thick fibrous root system of these grasses is associated with less infiltration capacity. (commonly associated with oat mottes), infiltration is rapid and immediate.

Model Predictions return periods based on 50 years climate data.
(Return)(Precip)(Runoff) (Erosion)
(Period)(in) (in) (t/ac)
---------------------------------
(50 yr) (52.7) (10.1) (1.3)
(25 yr) (49.5) (5.8) (1.1)
(10 yr) (44.5) (3.2) (0.6)
(5 yr) (40.1) (1.7) (0.3)
(2.5 yr)(35.6) (0.5) (0.1)
---------------------------------
(50 yr) (32.9) (0.9) (0.2)
(avg.)

Based on 50 years of climate data, there is an 82 percent chance there will be runoff and delivered sediment for these conditions. [Rangeland Hydrology and Erosion Model (RHEM) predictions—model calibrated from field data]. The average sediment to runoff ratio is (0.2/0.9 = 0.2. For every 1.0 inch of runoff, 0.2 t/ac soil erosion.

Community 1.2 Savannah Shrubland Community
This state is associated with 10 to 20 percent juniper canopy. There is also a shift to less desirable grasses. The consequence is that the hydrologic function decreases.

Model Predictions return periods based on 50 years climate data.
(Return)(Precip)(Runoff) (Erosion)
(Period)(in) (in) (t/ac)
---------------------------------
(50 yr) (52.7) (9.5) (4.3)
(25 yr) (49.5) (6.8) (2.7)
(10 yr) (44.5) (3.8) (2.1)
(5 yr) (40.1) (2.7) (1.0)
(2.5 yr)(35.6) (1.0) (0.6)
---------------------------------
(50 yr) (32.9) (1.4) (0.7)
(avg.)

Based on 50 years of climate data, there is a 98 percent chance there will be runoff and delivered sediment for these conditions. [Rangeland Hydrology and Erosion Model (RHEM) predictions—model calibrated from field data]. The average sediment to runoff ratio is (0.7/1.4 = 0.5. For every 1.0 inch of runoff, 0.5 t/ac soil erosion.

State 2: Oak-Juniper State
Woody species dominate the site in this community with Ashe juniper being the dominant plant.
Canopy exceeds 30 percent and shade tolerant species such as cedar sedge and uniola species dominate the understory that is void of sunlight. The majority of the soil surface on this densely canopied site will have a thick mat of cedar leaves and other woody tree and shrub leaf material. The open areas between canopies will produce a grass cover of primarily low successional species such as gramas, threeawns, tridens, and dropseeds. The total grasslike production potential for this community is severely restricted. These grasses do not protect the soil as the rooting systems are more shallow than the bluestems and other tall native grass species. Patches of bare ground become connected in the interspaces between trees. Plants become pedestalled and litter may be found in debris dams or lodged against rocks and brush. A significant amount of soil erosion occurs in these interspace areas and often the surface soil is severely depleted in old juniper stands.

(Return)(Precip)(Runoff) (Erosion)
(Period)(in) (in) (t/ac)
---------------------------------
(50 yr) (52.7) (11.8) (6.2)
(25 yr) (49.5) (7.4) (3.6)
(10 yr) (44.5) (4.1) (2.8)
(5 yr) (40.1) (3.5 (1.6)
(2.5 yr)(35.6) (1.7) (0.9)
---------------------------------
(50 yr) (32.9) (1.8) (1.1)
(avg.)

Based on 50 years of climate data, there is a 100 percent chance there will be runoff and delivered sediment for these conditions. [Rangeland Hydrology and Erosion Model (RHEM) predictions—model calibrated from field data]. The average sediment to runoff ratio is (1.1/1.8 = 0.6. For every 1.0 inch of runoff, 0.6 t/ac soil erosion.

Recreational uses

This site has the appeal of the wide open spaces. The abundant tall and mid grasses and scattered oaks produce beautiful fall color variations. The area is also used for hunting, birding, and other eco-tourism related enterprises.

Wood products

Honey mesquite and oaks can be used for firewood and the specialty wood industry.

Inventory data references

Information presented here has been derived from limited NRCS clipping data, field observations of range trained personnel and from research of historic observations.

Other references

References:

Anderson, J.R., C.A. Taylor, Jr., C.J. Owens, J.R. Jackson, D.K. Steele, and R. Brantley. 2013. Using experience and supplementation to increase juniper consumption by three different breeds of sheep. Rangeland Ecol. Management. 66:204-208. March.
Archer S. 1994. Woody plant encroachment into southwestern grasslands and savannas: rates, patterns and proximate causes. in: Ecological implications of livestock herbivory in the West, pp.13-68. Edited by M. Vavra, W. Laycock, R. Pieper, Society for Range Management Publication. , Denver, Colorado.
Bestelmeyer, B.T., J.R. Brown, K.M. Havsted, R. Alexander, G. Chavez, and J.E. Hedrick. 2003. Development and use of state-and-transition models for rangelands. Journal of Range Management. 56(2): 114-126.
Bushland, R.C. 1985. Eradication program in the southwestern United States. Symposium on eradication of the screwworm from the United States and Mexico. Misc. Pub. Entomol. Soc. Am., 62:12-15.
Foster, J.H. 1917. The spread of timbered areas in central Texas. Journal of Forestry 15:442-445.
Frost, C. C. 1998. Presettlement fire frequency regimes of the Unites States: a First Approximation. Tall Timbers Fire Ecology Conference Proceedings. No. 20. Tall Timbers Research Station. Tallahassee, FL.
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Hamilton W. and D. Ueckert. 2005. Rangeland Woody Plant Control--Past, Present, and Future. Chapter 1 in: Brush Management-Past, Present, and Future. Texas A & M University Press. Pp.3-16.
Hanselka, W., R. Lyons, and M. Moseley. 2009. Grazing Land Stewardship – A Manual for Texas Landowners. Texas AgriLife Communications, http://agrilifebookstore.org.
Hart, C., R.T. Garland, A.C. Barr, B.B. Carpenter, and J.C. Reagor. 2003. Toxic Plants of Texas. Texas Cooperative Extension Bulletin B-6103 11-03.
Inglis, J. M. 1964. A History of Vegetation on the Rio Grande Plains. Texas Parks and Wildlife Department, Bulletin No. 45. Austin, Texas.
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Plant symbols, common names, and scientific names according to USDA/NRCS Texas Plant List (Unpublished)
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Scifres, C.J. and W.T. Hamilton. 1993. Prescribed Burning for Brush Management: The South Texas Example. Texas A & M University Press, 245 pp.
Smeins, F., S. Fuhlendorf, and C. Taylor, Jr. 1997. Environmental and Land Use Changes: A Long Term Perspective. Chapter 1 in: Juniper Symposium 1997. Texas Agricultural Experiment Station. Pp 1-21.
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http://extension.usu.edu/behave/accessed 6/6/13

Contributors

Carl Englerth
Joe Franklin, ZRMS, NRCS,S an Angelo Zone Office, Texas
K E Spaeth
Mark Moseley
Ryan McClintock, Biologist, NRCS, San Angelo Zone Office, Texas
Jessica Jobe, MLRA Leader, NRCS, Kerrville Soil Survey Office, Texas
Travis Waiser, Soil Scientist, NRCS, Kerrville Soil Survey Office, Texas
Bryan Hummel, Natural Resources Technician, DoD, Joint Base San Antonio-Camp Bullis, Texas

Approval

Bryan Christensen, 9/19/2023

Acknowledgments

Site Development and Testing Plan:

Future work, as described in a Project Plan, to validate the information in this Provisional Ecological Site Description is needed. This will include field activities to collect low, medium and high-intensity sampling, soil correlations, and analysis of that data. Annual field reviews should be done by soil scientists and vegetation specialists. A final field review, peer review, quality control, and quality assurance reviews of the ESD will be needed to produce the final document. Annual reviews of the Project Plan are to be conducted by the Ecological Site Technical Team.

Reviewers and Technical Contributors:
Ann Graham Editor NRCS Temple, Texas

QC/QA completed by:
Bryan Christensen, SRESS, NRCS, Temple, TX
Erin Hourihan, ESDQS, NRCS, Temple, TX