Ecological dynamics

The reference plant community developed under the prevailing climate and conditions over time. This site is not generally a preferred site for grazing by livestock or wildlife due to lower plant palatability influenced by the limy nature of the soil. The high lime content limits the plant community to tolerant plant species. There are only minimal acres of the High Lime site in MLRA-77C of the Texas Panhandle and is considered a minor component of this MLRA. This site developed from the prevailing winds and wind blown deposits on the east and northeastern side of ancient playas and large basins. These playas were flooded periodically and served as temporary watering sites for large numbers of bison and resident pronghorn antelope. Occasional trampling and overgrazing likely occurred. Periodic droughts, fire, and grazing by resident wildlife prevalent in the area as well as nomadic creatures such as bison did influence the plant community.

The resulting Midgrass/Shortgrass Community (1.1) is a mixture of midgrass and shortgrass species with a few tallgrass species that can tolerate the limy nature of the soils. On some high lime sites, salinity can have a major influence on plant community composition. Only a few forbs and woody plants are typically found on this site. The dominant grasses are sideoats grama (Bouteloua curtipendula), blue grama (Bouteloua gracilis), vine mesquite (Panicum obtusum), western wheatgrass (Pascopyrum smithii), and alkali sacaton (Sporobolus airoides). Small amounts of little bluestem (Schizachyrium scoparium), switchgrass (Panicum virgatum) and sand bluestem (Andropogon hallii) can be found scattered throughout the site. Typical associated forbs include plains blackfoot daisy (Melampodium leucanthum), curlycup gumweed (Grindelia squarrosa) and dotted gayfeather (Liatris punctata) as well as numerous other annual and perennial forbs. Yucca (Yucca glauca), plains pricklypear (Opuntia spp.), and fourwing saltbush (Atriplex canescens) are often present with a few cholla cactus (Cylindropuntia imbricata) on parts of the site.

Periodic overgrazing and trampling by migrating herds of bison and resident herds of pronghorn antelope probably occurred only during wet periods when the playas and basins accumulated run-off water. This provided ideal watering and loafing areas for large numbers of herbivores. However, once the playas dried up, the herds would move out of the area. Long rest periods followed until the next big rainfall event. These rest periods allowed the vegetation to recover and maintain its historic climax plant community structure.

Fire has also played a part in the ecology of this site as with all plains sites. The main effect of fire on the High Lime site was to reduce old decadent plant cover from previous years, stimulate new shoots and increase diversity. Fire thus aided the nutrient cycle. Fire may have also helped in favoring the perennials over the annual species.

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

If excessive grazing continues, ecological retrogression occurs. As retrogression proceeds, this will bring about the Shortgrass/Midgrass/Annuals Community (1.2) with decreased amounts of low vigor sideoats grama and blue grama. Less palatable species such as alkali sacaton will increase along with inland saltgrass (Distichlis spicata), dropseed species (Sporobolus spp.) and perennial three-awn species (Aristida spp.). The better quality perennial forbs will be replaced with less desirable annual and perennial forbs.

The Shortgrass/Midgrass/Annuals Community (1.2) is reversible with proper grazing management and prescribed burning. The primary benefit of prescribed burning would be to reduce the excessive biomass of alkali sacaton and inland saltgrass and promote new sideoats grama and blue grama seedlings. Woody shrub canopies have generally not increased to the point where brush management is needed. Some areas may need selective brush management by chemical or mechanical means. There will be an increase in the percent bare ground scattered throughout the site.

If long-term heavy grazing continues, a threshold will be crossed to a Shrubs/Shortgrass/Annuals Community (2.1). This site will develop bare areas (>50 percent bare ground) and an increase in annuals. Some high lime sites may be invaded by broom snakeweed (Gutierrezia sarothrae) and mesquite (Prosopis glandulosa). Once established, these woody plants can increase to the point of domination. High Lime sites in the southern portion of MLRA 77C may be dominated by four-wing saltbush with heavy densities of mesquite scattered throughout the site. Salinity and lime content of the soil influences the woody invasion more than any other factor. Western ragweed (Ambrosia psilostachya) and sagewort (Artemesia spp.) may increase in some areas. The short and midgrass species that do remain will be in low vigor. 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 brush and pest management. Full recovery and maintenance of the reference community requires continued proper grazing management as well as occasional brush and pest management. Prescribed burning is also a useful tool in managing the reference community if adequate fine fuel is available to carry out an effective burn.

As mentioned earlier, this site is not preferred by livestock for grazing. The low palatability of the forage is influenced by the limey nature of the soil. Therefore, if livestock are being forced to overgraze this less preferred site, then there is obviously a grazing management problem on the surrounding associated sites. Livestock generally will not frequent this site unless all other available forage in the pasture has been removed.

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 lined box on 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.