Ecological dynamics

The plant communities that can occur on this site range from a Tallgrass/Midgrass dominant, live oak (Quercus fusiformis) and post oak (Quercus stellata) Savannah to a Midgrass Savannah, to an Ashe juniper (Juniperus ashei) and Mesquite (Prosopis glandulosa var. glandulosa) dominated mixed grass and/or shortgrass range, to a thick canopy Ashe juniper/mesquite/shrub short and annual grasses and forb complex community. This wide diversity of plant communities occurring on this site is in direct response to type of grazing management, the inherent selection of this site by all kinds of grazing animals due to its fertility in relation to other neighboring sites, reaction to fire regimes, extermination of the prairie dogs, and the impacts of droughts on the different hydrology’s associated with each of the steady states.

The reference plant community is a Tall/Midgrass Savannah Community of live oak and post oak that have a woody canopy of approximately ten percent. The major tallgrass species are big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoprium ssp. scoparium), Indiangrass (Sorghastrum nutans), and switchgrass (Panicum virgatum). These grasses dominate the site with a number of midgrasses such as sideoats grama (Bouteloua curtipendula var. curtipendula), tall dropseed (Sporobolus compositus var. compositus), cane bluestem (Bothriochloa barbinoidis var. barbinoidis), silver bluestem (Bothriochloa laguroides ssp. torreyana), vine-mesquite (Panicum obtusum), and cool-season grasses such as Canada wildrye (Elymus canadensis var. canadensis), Texas bluegrass (Poa arachnifera), and Texas wintergrass (Nassella leucotricha). There are numerous perennial forbs that share the landscape. Such forbs include Maximilian sunflower (Helianthus maximiliani), bush sunflower (Simsia calva), Englemann’s daisy (Engelmannia peristenia), dotted gayfeather (Liatris punctata var. punctata), blacksamson (Liatris punctata var. punctata), bundleflowers (Desmanthus sp.), heath aster (Chaetopappa ericoides), western ragweed (Ambrosia psilostachya), and legumes such as prairie clover (Dalea sp.), trailing wildbean (Strophostyles helvula), least snoutbean (Rhynchosia minima), tickclover (Desmodium sp.), and scurfpea (Pediomelum sp.). Besides the live oak and post oak, there are numerous other woody plants such as Texas oak (Quercus buckleyi), bigelow oak (Quercus sinuata var. breviloba), blackjack oak (Quercus marilandica), elm (Ulmus sp.), hackberry (Celtis laevigata), redbud (Cercus canadensis var. texensis) , bumelia (Sideroxylon lanuginosum), sumacs (Rhus sp.), elbowbush (Froestiera pubescens), agarito (Mahonia trifiolata), greenbriar (Smilax sp.), vine ephedra (Ephedra antisyphilitica), and bush honeysuckle (Lonicera albiflora).

In the reference plant community, tall and midgrasses dominated the shortgrasses due to their ability to capture sunlight and shade them. The tall and midgrasses also had deeper root systems that allowed them to capture the deep moisture while the shortgrasses had shorter root systems and could capture only the more shallow moisture. Many of the deep-rooted grasses also have more root hairs that allow them to be more efficient at extracting moisture from very dry soil. Due to these differences, the tall and midgrasses maintained their dominance over the shortgrasses as they could produce much more food and maintain a high state of health and vigor even in times of drought.

When European settlers arrived, the area was inhabited by bison, white-tailed deer, turkey, quail, dove, many song birds, rabbits, squirrel, prairie dogs, lizards and snakes. Fire was a major factor in maintaining the site in the reference state. Lightning fires, and fires set by Native Americans would burn for days with out stopping. Hundreds of thousands of acres would burn as there was nothing but wide spread rivers or a change in weather to stop them. This repeated burning kept the range in a savannah state, with only the large tall trees being spared a top kill. The re-sprouting shrubs, the fresh lush green growth of the grass and forbs made this range a sea of lush growth that attracted the grazing and browsing animals and provided them highly nutritious forage.

There were no fences. The bison were free to roam and migrate from south to north in the summer and north to south as the winter season was nearing. This area provided the winter grazing for the bison herds that had ventured north for the summer. They came by the thousands and grazed the range as they moved around. Antelope were on the range, and grazed and roamed at their desire, seeking the best nutrition they could find in the forbs and grasses. Prairie dogs lived in groups on the site. They kept the woody shrubs cut down as a means of protection from hawks, eagles, coyotes, bobcats, and cougars. Recent research has shown that they would not let a mesquite stand overnight that was planted in or around their town.

European settlers started settling this area in the early 1800’s with a major thrust just before and after the civil war. The first settlers moved about from ranch to ranch as no one owned land. After the grass was grazed to a point of “being gone”, they would move to another place where the grass was good and start another ranch. When the grass “came back” on the ranch they had left, a new rancher would move in and take over that ranch.

In 1880, barbed wire was introduced into this area. The land had also come under private ownership. The fencing stopped the open range, where livestock had wondered to be guided only by the line riders. Now the forces of contained livestock grazing started to have its toll on the plant communities. The wildfires that once systematically burned over the land were either put out or burned with less intensity due to reduced fine fuel due to the heavier and continuous grazing.

Depending on how the rancher managed, the plant communities started to change. If the rancher allowed fire to continue to control the Ashe juniper and mesquite seedlings, they could manage their rangeland to be classified as Tall/Midgrass Savannah Community. If fire was not allowed to maintain the invading brush species, the Ashe juniper and mesquite would encroach over the range as the many other shrubs natural to the site expanded in canopy. If it was burned prior to achieving approximately 6 feet in height, fire could be used to reclaim the land. If the brush was allowed to exceed 6 feet, then fire could no longer control the brush species and the range entered a new steady state that would require more than fire to reclaim it. The manager would have to use machinery or herbicides to manage the brush to a desired canopy.

Also, the manager would have to apply a well thought out prescribed grazing plan to maintain the vigor and health of the grasses and forbs that they desired on the range. As the stocking rates exceeded the carrying capacity of the land and the natural graze-rest cycles were broken by continuous grazing, the palatable and highly selected tallgrasses were grazed to the point that they could no longer produce sufficient food in their leaves to maintain their health and vigor. Records of stocking rates show that on much of the land, there was a cow to 2 acres. When the tallgrasses were grazed to the point that they had little leaf area left, they stopped supplying the root system with food, as all available food produced was going to grow more leaf area to enhance the food manufacturing process. If the overgrazing continued, the root system of the overgrazed plants continued to be used up and shrink, as respiration continued in the root system that required energy. In time, with continued close grazing, the tallgrasses would become not a deep rooted, healthy plant, but a very shallow rooted, small leaf area, weak plant that was set up for doom during the next drought. This process was intensified due to the natural droughts that occur in the area. These tallgrass plants were not now in a dominant position to the midgrasses, but in a position of being dominated by the midgrasses on the site. This then lead to the demise of the tallgrasses and an increase of mid and shortgrasses on the site. These midgrasses were sideoats grama, cane bluestem, silver bluestem and vine-mesquite. At the same time this was occurring with the grasses, the palatable forbs were being overgrazed and killed out of the plant community.

If the new steady state of cedar and mesquite and mixed grasses was overgrazed and no brush was controlled, the site would evolve to a canopy of 30 to 50 percent, with mainly buffalograss, Texas wintergrass and other short grasses in the understory. If this management was allowed to continue, the site would change to a dense canopy of juniper and mesquite, shortgrasses and invading forbs and annual cool-season grasses.

Since the soils of this site are very productive and fertile, much of this site has been plowed and put into cropland. In many instances, this land has either been reseeded to native grasses, introduced grasses or just turned out to let come back what could. Many times this turned out land, also known as Abandoned or Go Back land, was planted to native or introduced grasses when it was found that it was not very productive growing the annual grasses and forbs.

After the land was planted to native or introduced grasses and forbs, management of the land to control the invasion of Ashe juniper and mesquite from neighboring lands was a must if the manager desired to keep the open land. This could be accomplished with prescribed burning or other means of brush management. Also, to maintain the stand of native or introduced grasses planted, a prescribed grazing plan must be designed and applied that meets the needs of the plants, the animals and the managers objectives.