Ecological dynamics

This is an upland site found on ridges, along draws, and on low escarpments within a rolling plains aspect. In historic climax, it is dominated by mid-grasses with a large compliment of short-grasses and perennial forbs, along with a variety of short shrubs. There are a few tallgrasses present in areas of more favorable moisture regime, such as in small depressions where some soil material has accumulated. Many of the short shrubs appear to have their origin in the larger cracks in the sandstone parent material. There is probably both soil material and moisture accumulation in some of these cracks that make germination and establishment of shrubs possible. Plant basal cover is generally sparse, but varies within the site. Lack of inherent fertility may render some plant species less palatable on this site as compared to sites with deeper soils. Over-utilization by herbivores, especially cattle, is not as likely to be a serious problem compared with some of the more productive, adjacent sites. There is a good diversity of species and these are well distributed between grasses, forbs, and short shrubs. In general, this site does produce some valuable browse plants for deer and pronghorn. It is not an extensive site, usually being of rather small acreages. It is unique and very instructive in the areas of geology and plant diversity.

The historic plant community is basically mid-grasses and short-grasses, with several short-statured shrubs present. Grasses consist of sideoats grama (Bouteloua curtipendula), little bluestem (Schizachyrium scoparium), blue grama (Bouteloua gracilis), hairy grama (Bouteloua hirsuta), black grama (Bouteloua eriopoda), galleta (Pleuraphis jamesii), wolftail (Lycurus phleoides), sand dropseed (Sporobolus cryptandrus), New Mexico feathergrass (Hesperostipa neomexicana), and perennial threeawn (Aristida sp.). A few tallgrasses such as sand bluestem (Andropogon hallii) and Indiangrass (Sorghastrum nutans) are present in micro-environments where extra runoff can accumulate. Major forb species include plains actinea (Tetraneuris scaposa), dotted gayfeather (Liatris punctata), plains blackfoot (Melampodium leucanthum), Mexican sagewort (Artemisia ludoviciana), sand lily (Mentzelia nuda), baby white aster (Leucelene ericoides), plains zinnia (Zinnia grandiflora), broom nailwort (Paronychia jamesii), and broom snakeweed (Gutierrezia sarothrae). Shrubs include feather dalea (Dalea formosa), skunkbush sumac (Rhus aromatica), plains greasebush (Glossopetalum planitierum), catclaw mimosa (Mimosa aculeaticarpa var. biuncifera), and vine ephedra (Ephedra antisyphilitica). Brownspine pricklypear (Cylindropuntia californica) is the most common cactus. Occasional shrubby mesquite (Prosopis glandulosa) occurs as well. There are rare occurances of small hackberry (Celtis laegivata reticulata) and western soapberry (Sapindus saponaria).

In addition to the sandstone-derived soils, the ecology of the site has been shaped by climate and, perhaps to a lesser degree, by natural fires. The harsh climatic extremes play a major role in determining the mixture of species occupying the site. Limited rainfall, high evaporation rates, and almost constant winds demand a plant community of tough, deep-rooted perennial species. Periodic drought and temperature extremes also play a major role in determining the climax plant community. Natural fire was a factor in site ecology, but probably played less of a role on this site than on adjacent sites that produced greater quantities of fine fuel and provided the kind of fuel continuity necessary to carry a fire. The sparseness of vegetation and the accompanying rock cover on the site would hinder fire movement. In general, it is thought that wildfires occurred in this region every 8 to 15 years on the average.

In above-average rainfall years, portions of the site would have produced sufficient fine fuel to burn, but it is unlikely that much of the site would ever be exposed to fire.

In observing recent wildfires that have occurred, areas of the Shallow Sandstone site are generally left unburned. It is possible that protection from the intense natural fires partially explains the diversity of short shrubs present on the site, although there may be other explanations.

Large herbivores such as bison, elk, pronghorn, and mule deer were present in pre-settlement times and mule deer and pronghorn can still be found today. When the bison migrated through the area in huge herds, vegetation was subjected to heavy periodic grazing pressure and trampling. Old bison trails are still visible cutting across some of the sandstone slabs making up this site. Periodic grazing and browsing by large herbivores followed by long recovery periods helped to shape the historic plant community. Small herbivores such as rabbits, ground squirrel, and various species of mice and voles used the site to forage and to take refuge in cracks in the rocks and beneath the numerous overhangs. Predators like the coyote, fox, lobo wolf, and even bear were common in pre-settlement times, and ringtails and raccoons like to forage in the rocks and clefts. All these except the wolf and the bear are still present. Native Americans sometimes left their artwork chiseled into the sandstone rocks located near water sources.

Over time, naturally occurring geologic erosion has changed this site. As soil is removed by the action of water and wind, and more sandstone rock exposed, the plant community is called upon to adapt and change also. As erosion occurs, small areas of deposition also occur. Plants take advantage of this and form small colonies in these more favorable micro-climates. Since this site produces a good variety of browse species, pressure from a growing deer or pronghorn population might occur, but this is usually not evident today. It is possible that heavy grazing by sheep in the late 1800’s could have had an effect on the plant community, but there have been no sheep present in this region for over 100 years.

The assumed historic plant community for this site can be found on well-managed ranches in this MLRA. Since abusive grazing by livestock is rare on this site, and there does not appear to be any significant invasion of cacti or documented increase of woody shrubs, there is no conclusive evidence that the plant community was much different in pre-settlement times. There are sometimes individual sites where there are a few oneseed junipers present, but this does not appear to be due to any management-related cause. In centuries past, the bison may have disturbed these sites by trampling more than any present day domestic livestock activity. Soil type and climate (including severe drought conditions) are probably the greatest influencing factors to the plant community. However, abusive grazing practices could certainly play a part in site deterioration. If the adjacent, more-productive and preferred sites were to be abused, then livestock could be forced to utilize the shallow sandstone site, when under proper stocking and prescribed grazing, it would be little-utilized. There are some subtle changes from one particular shallow sandstone site to another, with one of the noticeable differences being the amount and species of short shrubs present. There are portions of the site where shrubs may visually be the dominant class of vegetation, and other areas where grasses and forbs dominate. These differences appear to be within natural ranges.

This is a unique site both geologically and vegetatively. The historic climax plant community exhibits considerable species diversity, and the soil forming processes and the hydrologic processes can be observed more readily here than on other sites in the MLRA. Although damage from livestock traffic would be rare, the land user should be conscious of the fragile plant community on selected areas. Improper land treatment could accelerate erosion and lead to site deterioration. As previously stated, over-browsing by deer (or sheep and goats) could negatively affect the vegetative resource on the site.

NOTE: Rangeland Health Reference Worksheets have been posted for this site on the Texas NRCS website (www.tx.nrcs.usda.gov) in Section II of the FOTG under (F) Ecological Site Descriptions.

Narrative:
The following diagram suggests some pathways that the vegetation on this site might take. There may be other states not shown on the diagram. This information is intended to show what might happen in a given set of circumstances; it does not mean that this would happen the same way in every instance. Local professional guidance should always be sought before pursuing a treatment scenario.

*As stated in the ecological dynamics section, the plant communities occurring on this site are most dependent on climate, the extent of soil development, and hydrologic factors. Management and fire played a secondary role.