Ecological dynamics

The information contained in the State and Transition Diagram (STD) and the Ecological Site Description was developed using archeological and historical data, professional experience, and scientific studies. The information presented is representative of a very complex set of plant communities. Not all scenarios or plants are included. Key indicator plants, animals and ecological processes are described to inform land management decisions.
The reference plant community for this site is a mixture of tallgrasses, midgrasses, perennial forbs and a small amount of woody shrubs. It is a very diverse site and is capable of relatively high production when well managed. Plant available water is high due to moderately coarse soils and the lime content seems to favor plants like little bluestem (Schizachyrium scoparium) and sideoats grama (Bouteloua curtipendula). The other major grass species include sand bluestem (Andropogon hallii), Indiangrass (Sorghastrum nutans), switchgrass (Panicum virgatum), and assorted midgrass species. There are many perennial forb species present, including prairie clovers (Dalea spp.), daleas (Daleas spp.), Engelmann's daisy (Engelmannia peristenia), scurfpea (Psoralidium teniuflorum), sensitive briar (Mimosa spp.), gaura (Gaura spp.), bush morning-glory (Ipomoea leptophylla), spiderwort (Tradescantia spp.), dayflower (Commelina spp.) and many others. The main shrubs found on the site are sand sagebrush (Artemisia filifolia) and skunkbush sumac (Rhus tribolata). Infrequent sand plum (Prunus angustifolia) thickets and scattered yucca (Yucca spp.) also occur. Occasionally leadplant (Amorpha canescens) and inland ceanothus (Ceanothus herbaceus) can be found on well-managed sites. Trees are scarce but occasional hackberry (Celtis spp.), cottonwood (Populus spp.), and western soapberry (Sapindus saponaria) may be observed. The production and variety make this site excellent habitat for quail, deer, prairie chicken, and pronghorn and a preferred grazing site for domestic livestock, especially cattle.

Natural fires played a major role in the development and maintenance of the tallgrasses and generally helped keep woody shrubs suppressed. In the total absence of fire, shrubs tend to increase although slowly. With grazing abuse, exacerbated by weather extremes and absence of fire the shrub encroachment is more rapid. Generally this site in good ecological condition will produce enough fine fuel for fires to offer considerable suppression to woody vegetation.

All sites in this region developed under a fire/grazing interaction ecology. Large herbivores grazed the grasslands, especially following burns, and moved on seeking fresh forage. Recovery took place naturally because it is anticipated that sufficient recovery time usually took place before the animals returned to graze the same area again. Prescribed grazing techniques can somewhat simulate this natural process.

This is a preferred site for domestic livestock and overgrazing can easily occur. If the tallgrasses and palatable forbs are pressured for several years, plant succession will trend more toward midgrasses and shrubs. In instances of prolonged, severe grazing abuse, the site will revert to moderate canopies of sand sagebrush and short grass species. This site is diverse and productive, but perhaps not as resistant to ecological shifts in vegetation as the shortgrass sites that are associated with it. If the tallgrasses decline, midgrasses increase and shrub encroachment begins, the balance can be influenced toward the reference community by planned rest periods and the use of prescribed fire. In the absence of prescribed fire, the application of judicious chemical brush management can often produce similar results. The time period necessary to affect these kinds of vegetative changes is usually 3 to 4 years. Once midgrasses and a significant canopy of sagebrush dominate the site, a return to tallgrass dominance will seldom happen without brush management and growing season rest. This process may take as much as 5 to 6 years with careful grazing management. If the vegetative state reaches the sagebrush - shortgrass dominance, it is certainly indicative of severe grazing abuse for many years. The site may remain stable in the sagebrush-shortgrass state, but it is neither productive nor diverse. Restoring a tall and midgrass community may be difficult once the vegetation reaches the shortgrass shrub state. Reseeding may be feasible in some cases, but success depends on environmental conditions at the time, and the subsequent control of competing vegetation.

In the more diverse vegetative states, a variety of wildlife utilizes this site. The diversity of plant species makes this good habitat for quail, deer, pronghorn and lesser prairie chicken. Cover may be somewhat deficient for deer, but other sites in close proximity of this site may provide ample cover of woody vegetation. The quality of habitat is generally better for most species if the site is maintained as a tall and midgrass community. An exception to this might be quail, which prefer a lower ecological condition with more annual forbs as long as other habitat components exist on adjacent sites. Domestic livestock performance is much better if the tall and midgrass community is maintained. Ecological processes such as the nutrient cycle and the hydrological cycle are enhanced by the maintenance of a diverse, higher producing plant community.

State and Transition Diagram:
A State and Transition Diagram for the Mixedland Slopes (R077EY061TX) site is depicted below. Thorough descriptions of each state, transition, and pathway follow the model. Experts base this model on available experimental research, field observations, professional consensus, and interpretations. It is likely to change as knowledge increases.
Plant communities will differ across the MLRA because of the natural variability in weather, soils, and aspect. The Reference Plant Community is not necessarily the management goal; other vegetative states may be desired plant communities as long as the Range Health assessments are in the moderate and above category.

The biological processes on this site are complex. Therefore, representative values are presented in a land management context. The species lists are representative and are not botanical descriptions of all species occurring, or potentially occurring, on this site. They are not intended to cover every situation or the full range of conditions, species, and responses for the site.

Composition by dry weight and percent canopy cover are provided to describing the functional groups. Most observers find it easier to visualize or estimate percent canopy for woody species (trees and shrubs).

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.