Ecological dynamics

The soils, topographic location, climate, periodic droughts and fire influenced the stabilization of the reference plant community on this site as was the case on most all High Plains ecological sites. This plant community as found by European settlers in the early 1800’s developed under the prevailing climate over time along with the soils in their topographic location. Grazing and/or browsing by local and nomadic wildlife influenced the plant community as well. The resulting plant community is a Midgrass/Shortgrass Community (1.1). The sandy loam site is quite possibly the most productive site in the Texas Panhandle. Midgrasses tend to dominate over most of the site with sideoats grama (Bouteloua curtipendula) being the overall dominant species. Lesser amounts of vine-mesquite (Panicum obtusum), Arizona cottontop (Digitaria californica), plains bristlegrass (Setaria leucopila), hooded windmillgrass (Chloris cucullata), sand dropseed (Sporobolus cryptandrus), tumble windmillgrass (Chloris verticillata), silver bluestem (Bothriochloa laguroides), hairy grama (Bouteloua hirsuta), fall witchgrass (Digitaria cognata), gummy lovegrass (Eragrostis curtipedicellata), black grama (Bouteloua eriopoda), and sand muhly (Muhlenbergia arenicola) are present. Little bluestem (Schizachyrium scoparium)is present with lesser amounts of Indiangrass (Sorghastrum nutans) and sand bluestem (Andropogon hallii). In areas where tighter soils occur, the shortgrasses are blue grama (Bouteloua gracilis) and buffalograss (Bouteloua dactyloides). Some cool-season grasses occurr in small amounts such as western wheatgrass (Pascopyrum smithii), Canada wildrye (Elymus canadensis) and needle & thread (Hesperostipa comata). Typically associated forbs include dotted gayfeather (Liatris punctata), prairie clover (Dalea purpurea), catclaw sensitivebriar (Mimosa microphylla), golden dalea (Dalea aurea), gaura (Gaura spp.), rushpea (Hoffmanseggia glauca), Engelmann’s daisy (Engelmannia peristenia), lyreleaf greeneyes (Berlandiera lyrata), sagewort (Artemisia ludoviciana), scarlet globemallow (Sphaeralcea coccinea), Fendler’s penstemon (Penstemon fendleri), wild alfalfa (Psoralidium tenuiflorum) and numerous annual forbs. Woody species include sand sagebrush (Artemesia filifolia), yucca (Yucca glauca), and catclaw mimosa (Mimosa aculeaticarpa var. biuncifera). Nutrient cycling, the water cycle, watershed protection and biological functions were functioning at their peak.

Fire plays an important role in the function of most plains sites, especially the tallgrass communities. Tallgrasses such as sand bluestem and little bluestem were dependent upon fire to stimulate them and remove old growth that would accumulate on the soil surface. Fire also keeps shrubs from getting too thick. Fire helps to keep a balance between the grasses, forbs, and shrubs. Wildlife habitat is improved by opening up canopies and stimulating forb growth. The deep-rooted species that grow on the site are not easily damaged by fire. Yucca and associated shrubs will usually resprout, but are suppressed for a time allowing grasses to dominate. If periodic fire does not occur, then the yucca and woody plants will slowly increase and with grazing pressure can begin to dominate the site. Since fire is not always available to be applied, practices such as brush management may necessary from time to time to help keep the community in balance.

Periodic grazing and trampling by migrating herds of bison and resident herds of pronghorn antelope probably occurred during drought periods. However, long rest periods followed once the large herds of bison and antelope moved out of the area, allowing the resilient grassland to re-establish itself and maintain its climax community structure.

The major forces influencing the transition from the reference community are continued overgrazing by livestock and a decrease in the frequency and intensity of fire. As livestock and wildlife numbers increase and grazing use exceeds a plants ability to sustain defoliation, the more palatable and generally more productive species decline in stature, productivity and density.

Under good management this is one of the most productive sites in the Texas Panhandle and will give good animal performance. Little bluestem and sideoats grama are fairly resistant to grazing pressure but will decline if continuous heavy grazing persists. The tallgrasses are fairly sensitive to overgrazing and will begin to decrease more quickly if continuous abusive grazing occurs for long periods. If excessive grazing pressure continues, ecological retrogression occurs. The tendency of this site, as excessive grazing pressure occurs, is to become a shortgrass dominant site, allowing sideoats grama and little bluestem to give way to blue grama. There will be an increase in perennial and annual forbs, and perennial three-awn will increase. Yucca and sand sagebrush tend to increase. Invasion of mesquite, broom snakeweed and pricklypear may occur on some sites. The decrease in density and stature of the midgrasses and tallgrasses and an increase in shortgrasses and the density of the yucca and woody vegetation bring about a new plant community, the Shortgrass Community (2.1).

In the Shortgrass Community (2.1), the transition back to the reference community requires proper grazing management, brush management, and pest management. Prescribed burning could be used if the conditions allow. The production of vegetation has shifted from mostly herbaceous vegetation to more yucca and woody, although the herbaceous vegetation biomass is still the largest amount. Nutrient cycling, the water cycle, watershed protection and biological functions have changed little.

If long-term abusive grazing continues, a threshold will be crossed to a Degraded Shortgrass Community (3.1). In this degraded state, typical vegetation will be low vigor blue grama with bare areas opening up with annuals filling the voids. Perennial three-awn will increase when the more desirable grasses are weakened and/or removed. Yucca and sand sagebrush will increase dramatically. On sites where mesquite, pricklypear and broom snakeweed have invaded, these woody invaders can increase to the point of dominating the woody canopy. The loss of herbaceous cover and increased bare ground encourages accelerated erosion. Nutrient cycling, the water cycle, watershed protection and biological functions have been severely reduced. The plant community is so degraded that it cannot reverse retrogression without extensive energy and management inputs. Restoration will require prescribed grazing with rest periods during the growing season, re-seeding bare areas with adapted native grass species, and chemical and/or mechanical brush management and some form of pest management. With the reduced amounts of grass fuel, prescribed burning is usually not an option in this phase.

Recovery can occur fairly rapidly if the competitive plants are controlled and proper grazing management is applied. Full recovery and maintenance of the reference community requires continued proper grazing management as well as occasional brush and pest management.

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 eFOTG under (F) Ecological Site Descriptions.

STATE AND TRANSITIONAL PATHWAYS

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.

Changes in the structure and composition of the plant community may be due to management and/or natural occurrences. At some point thresholds are crossed as indicated by the State and Transition Diagram. This suggests that once changes have progressed to a certain point, the plant community has been altered to the extent that a return to the former state is not possible unless some form of energy is applied. These changes take place on all ecological sites. Some sites support communities that are more resistant to change than others. Also, some sites are more resilient and can heal or restore themselves more easily. Usually, changes in management practices alone, such as grazing techniques, will not be sufficient to restore former plant communities. An example of energy input might be the implementation of chemical brush management to decrease the amount of woody/cacti shrubs and increase the amount of grasses and forbs. This shift in community balance could not be brought about with grazing alone. The amount of energy required to bring about a change in plant community balance may vary a great deal depending on the present state and the desired result.