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Conservation Service

Ecological site R083AY001TX

Igneous Hill

Last updated: 9/19/2023
Accessed: 11/23/2024

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General information

Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.

MLRA notes

Major Land Resource Area (MLRA): 083A–Northern Rio Grande Plain

This area is entirely in Texas and south of San Antonio. It makes up about 11,115 square miles (28,805 square kilometers). The towns of Uvalde, Cotulla, and Hondo are in the western part of the area, and Beeville, Goliad, and Kenedy are in the eastern part. The town of Alice is just outside the southern edge of the area. Interstate Highways 35 and 37 cross this area. This area is comprised of inland, dissected coastal plains.

Classification relationships

USDA-Natural Resources Conservation Service, 2006.
-Major Land Resource Area (MLRA) 83A

Ecological site concept

Sites are on uplands with greater than 15 percent gravels throughout the soil profile. The high amount of gravels are unique to the area.

Associated sites

R083AY002TX	Shallow Ridge
R083AY004TX	Shallow Sandy Loam

R083AY002TX

Shallow Ridge

R083AY004TX

Shallow Sandy Loam

Similar sites

R083BY001TX	Igneous Hill

R083BY001TX

Igneous Hill

Table 1. Dominant plant species

Tree	Not specified
Shrub	Not specified
Herbaceous	(1) Digitaria californica (2) Bouteloua curtipendula

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Physiographic features

These are upland soils with slopes ranging from 0 to 30 percent. Runoff is very low to very high dependent on slope. Landscape is inland, dissected coastal plains

Table 2. Representative physiographic features

Landforms	(1) Coastal plain > Hill
Runoff class	High to very high
Elevation	123 – 140 m
Slope	3 – 19%
Aspect	Aspect is not a significant factor

Climatic features

MLRA 83A is subtropical, subhumid on the western boundary and subtropical humid on the eastern boundary. Winters are dry and mild and the summers are hot and humid. Tropical maritime air masses predominate throughout spring, summer, and fall. Modified polar air masses exert considerable influence during winter, creating a continental climate characterized by large variations in temperature. Average precipitation for MLRA 83A is 20 inches on the western boundary and 35 inches on the eastern boundary. Peak rainfall, because of rain showers, occurs late in spring and a secondary peak occurs early in fall. Heavy thunderstorm activities increase in April, May, and June. July is hot and dry with little weather variations. Rainfall increases again in late August and September as tropical disturbances increase and become more frequent. Tropical air masses from the Gulf of Mexico dominate during the spring, summer, and fall. Prevailing winds are southerly to southeasterly throughout the year except in December when winds are predominately northerly.

Table 3. Representative climatic features

Frost-free period (characteristic range)	221-246 days
Freeze-free period (characteristic range)	263-365 days
Precipitation total (characteristic range)	635-813 mm
Frost-free period (actual range)	207-262 days
Freeze-free period (actual range)	254-365 days
Precipitation total (actual range)	610-940 mm
Frost-free period (average)	233 days
Freeze-free period (average)	311 days
Precipitation total (average)	737 mm

Characteristic range

Actual range

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Figure 1. Monthly precipitation range

Characteristic range

Actual range

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Figure 2. Monthly minimum temperature range

Characteristic range

Actual range

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Figure 3. Monthly maximum temperature range

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Figure 4. Monthly average minimum and maximum temperature

Figure 5. Annual precipitation pattern

Figure 6. Annual average temperature pattern

Climate stations used

(1) PLEASANTON [USC00417111], Pleasanton, TX
(2) HONDO MUNI AP [USW00012962], Hondo, TX
(3) CARRIZO SPRINGS 3W [USC00411486], Carrizo Springs, TX
(4) CHARLOTTE 5 NNW [USC00411663], Charlotte, TX
(5) MATHIS 4 SSW [USC00415661], Mathis, TX
(6) TILDEN 4 SSE [USC00419031], Tilden, TX
(7) UVALDE 3 SW [USC00419268], Uvalde, TX
(8) FOWLERTON [USC00413299], Fowlerton, TX
(9) HONDO [USC00414254], Hondo, TX
(10) KARNES CITY 2N [USC00414696], Karnes City, TX
(11) PEARSALL [USC00416879], Pearsall, TX
(12) POTEET [USC00417215], Poteet, TX
(13) BEEVILLE 5 NE [USC00410639], Beeville, TX
(14) CHEAPSIDE [USC00411671], Gonzales, TX
(15) CUERO [USC00412173], Cuero, TX
(16) GOLIAD [USC00413618], Goliad, TX
(17) NIXON [USC00416368], Stockdale, TX
(18) CROSS [USC00412125], Tilden, TX
(19) DILLEY [USC00412458], Dilley, TX
(20) FLORESVILLE [USC00413201], Floresville, TX
(21) LYTLE 3W [USC00415454], Natalia, TX

Soil features

The soils are moderately deep, well drained, slowly permeable soils that formed in basalt. They are unique to area and Ingram is the only soil correlated to the site. The Ingram soil series is classified as a fine, mixed, active, hyperthermic Torrertic Haplustolls.

Table 4. Representative soil features

Parent material	(1) Residuum – basalt
Surface texture	(1) Stony clay (2) Gravelly clay
Family particle size	(1) Clayey
Drainage class	Well drained
Permeability class	Slow
Soil depth	51 – 97 cm
Surface fragment cover <=3"	15 – 20%
Surface fragment cover >3"	15 – 20%
Available water capacity (0-101.6cm)	12.7 cm
Calcium carbonate equivalent (0-101.6cm)	0 – 15%
Electrical conductivity (0-101.6cm)	0 – 2 mmhos/cm
Sodium adsorption ratio (0-101.6cm)	0
Soil reaction (1:1 water) (0-101.6cm)	6.6 – 8.4
Subsurface fragment volume <=3" (Depth not specified)	10 – 20%
Subsurface fragment volume >3" (Depth not specified)	5 – 20%

Ecological dynamics

The Northern Rio Grande Plain MLRA was a disturbance-maintained system. Prior to European settlement (pre-1825), fire and grazing were the two primary forms of disturbance. Grazing by large herbivores included antelope, deer, and small herds of bison. The infrequent but intense, short-duration grazing by these species suppressed woody species and invigorated herbaceous species. The herbaceous savannah species adapted to fire and grazing disturbances by maintaining belowground tissues. Wright and Bailey (1982) report that there are no reliable records of fire frequency for the Rio Grande Plains because there are no trees to carry fire scars from which to estimate fire frequency. Because savannah grassland is typically of level or rolling topography, a natural fire frequency of three to seven years seems reasonable for this site.

Precipitation patterns are highly variable. Long-term droughts, occurring three to four times per century, cause shifts in species composition by causing die-off of seedlings, less drought-tolerant species, and some woody species. Droughts also reduce biomass production and create open space, which is colonized by opportunistic species when precipitation increases. Wet periods allow midgrasses to increase in dominance.

Historical accounts prior to 1800 identify grazing by herds of wild horses, followed by heavy grazing by sheep and cattle as settlement progressed. Grazing on early ranches changed natural graze-rest cycles to continuous grazing and stocking rates exceeded the carrying capacity. These shifts in grazing intensity and the removal of rest from the system reduced plant vigor for the most palatable species, which on this site were mid-grasses and palatable forbs. Shortgrasses and less palatable forbs began to dominate the site. This shift resulted in lower fuel loads, which reduced fire frequency and intensity. The reduction in fires resulted in an increase in size and density of woody species.

Today, primarily beef cattle graze rangeland and pastureland. However, horse numbers are increasing rapidly on small acreage properties in the region. There are some areas where dairy cattle, poultry, goats, and sheep are locally important. Whitetail deer, wild turkey, bobwhite quail, and dove are the major wildlife species, and hunting leases are a major source of income for many landowners in this area. Introduced pasture has been established on many acres of old cropland and in areas with deeper soils. Buffelgrass is the most common introduced plant on the site and to a lesser extent bermudagrass, guineagrass (Urochloa maxima), and kleingrass, which are more commonly used for hay. Cropland is found in the valleys, bottomlands, and deeper upland soils. Wheat (Triticum spp.), oats Avena spp.), forage and grain sorghum (Sorghum spp.), cotton (Gossypium spp.), and corn (Zea mays) are major crops in the region.

State and transition model

Custom diagram

Standard diagram

Figure 7. STM

More interactive model formats are also available. View Interactive Models

More interactive model formats are also available. View Interactive Models
Click on state and transition labels to scroll to the respective text

Ecosystem states

1. Grassland

2. Shrubland

T1A	-	Absence of disturbance and natural regeneration over time, excessive grazing pressure, may be coupled with prolong drought
R2A	-	Removal of woody canopy, appropriate rest from defoliation, and release from drought

State 1 submodel, plant communities

1.1. Midgrass

State 2 submodel, plant communities

2.1. Shrubland

State 1
Grassland

Dominant plant species

Arizona cottontop (Digitaria californica), grass
sideoats grama (Bouteloua curtipendula), grass
silver bluestem (Bothriochloa saccharoides), grass

Community 1.1
Midgrass

Vegetation consist of grasses like Arizona cottontop (Digitaria californica), sideoats grama (Bouteloua curtipendula), silver bluestem (Bothriochloa saccharoides), curly-mesquite (Hilaria belangeri), plains bristlegrass (Setaria vulpsieta), and buffalograss (Buchloe dactyloides). The high amounts of gravels in the soil profile make this site droughty and shrubby. Shrubs will be present, but less than 40 percent. Prescribed grazing and fire will be necessary to keep woody species from overdeveloping.

State 2
Shrubland

Dominant plant species

guajillo (Acacia berlandieri), shrub
Texas lignum-vitae (Guaiacum angustifolium), shrub
whitebrush (Aloysia gratissima), shrub

Community 2.1
Shrubland

Heavy grazing and drought will cause woody species to increase. The palatable midgrasses are grazed out and only shortgrasses remain. Common shrubs include, guajillo, guayacan, white brush, spiny hackberry, blackbrush, and pricklypear.

Transition T1A
State 1 to 2

Heavy continuous grazing, lack of fire, and drought will transition this site into a Shrubland State (2). The site is characterized by greater than 40 percent woody canopy cover.

Restoration pathway R2A
State 2 to 1

Prescribed grazing and brush management are required to restore the community back to a Grassland State (1). Removal of woody species below 30 percent allows more light and nutrients to herbaceous species. Reducing grazing pressure will allow plants to regain vigor and re-establish.

Additional community tables

Interpretations

Animal community

As a historic tall/midgrass prairie, this site was occupied by bison, antelope, deer, quail, turkey, and dove. This site was also used by many species of grassland songbirds, migratory waterfowl, and coyotes. This site now provides forage for livestock and is still used by quail, dove, migratory waterfowl, grassland birds, coyotes, and deer.

Feral hogs (Sus scrofa) can be found on most ecological sites in Texas. Damage caused by feral hogs each year includes, crop damage by rutting up crops, destroyed fences, livestock watering areas, and predation on native wildlife, and ground-nesting birds. Feral hogs have few natural predators, thus allowing their population to grow to high numbers.

Wildlife habitat is a complex of many different plant communities and ecological sites across the landscape. Most animals use the landscape differently to find food, shelter, protection, and mates. Working on a conservation plan for the whole property, with a local professional, will help managers make the decisions that allow them to realize their goals for wildlife and livestock.

Grassland State (1): This state provides the maximum amount of forage for livestock such as cattle. It is also utilized by deer, quail and other birds as a source of food. When a site is in the reference plant community phase (1.1) it will also be used by some birds for nesting, if other habitat requirements like thermal and escape cover are near.

Tree/Shrubland Complex (2): This state can be maintained to meet the habitat requirements of cattle and wildlife. Land managers can find a balance that meets their goals and allows them flexibility to manage for livestock and wildlife. Forbs for deer and birds like quail will be more plentiful in this state. There will also be more trees and shrubs to provide thermal and escape cover for birds as well as cover for deer.

Supporting information

Inventory data references

Information presented was derived from the revised Range Site, literature, limited NRCS clipping data (417s), field observations, and personal contacts with range-trained personnel.

Other references

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Archer, S. 1994. Woody plant encroachment into southwestern grasslands and savannas: rates, patterns and proximate causes. Ecological implications of livestock herbivory in the West, 13-68.

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Contributors

Edited by Gary Harris, SPSD Soil Survey Region 9

Approval

Bryan Christensen, 9/19/2023

Rangeland health reference sheet

Interpreting Indicators of Rangeland Health is a qualitative assessment protocol used to determine ecosystem condition based on benchmark characteristics described in the Reference Sheet. A suite of 17 (or more) indicators are typically considered in an assessment. The ecological site(s) representative of an assessment location must be known prior to applying the protocol and must be verified based on soils and climate. Current plant community cannot be used to identify the ecological site.

Author(s)/participant(s)
Contact for lead author
Date	11/23/2024
Approved by	Bryan Christensen
Approval date
Composition (Indicators 10 and 12) based on	Annual Production