Ecological dynamics

The Loamy Sand ecological site occurs on uplands in the Rolling Red Plains. The parent material is sandy outwash or old alluvial deposits. Slopes vary, but typically fall in the 1-5% slope range. Infiltration is moderate to rapid with low runoff. Water erosion susceptibility is slight, but wind erosion potential is severe without good plant cover. The loamy sand soils have a moderately low water holding capacity, and are low in fertility but have a good plant, soil moisture, and air relationship. Plant basal cover is moderate, and can vary depending on moisture conditions.

The climate varies in temperature and rainfall from hot, dry summers to cool moist conditions, depending on seasonal weather patterns. In general, more rain falls in May and June, followed by hot, dry, and often windy July and August. Moisture in the fall varies greatly depending on storm systems that develop during the season. Drought conditions occur and some are severe, lasting several years, as in the “Dust Bowl” of the 1930’s and the 1950 – 1957 drought. Naturally occurring fires shaped the ecology of this site. Dry lightning storms move across the plains, generally from west to east in the early spring and in mid-to-late fall. Random lightning strikes may cause fires that travel for miles. These fires are thought to have occurred on average once every 7-12years.

Large herbivores such as bison, elk, pronghorn and deer existed on the Rolling Plains, with large migrations of bison herds grazing in high densities for short periods of time, then moving on to fresh, green vegetation. It is anticipated that these grazing events were closely tied to fire frequency. Minor herbivores such as jackrabbits, cottontail rabbit, ground squirrels, prairie dogs as well as various species of rats, mice and voles benefited from the vegetation of this site. Native American cultures depended on the bison for the majority of their sustenance. The bison provided meat, hides for shelter and clothing, and bone for tools and weapons. The hunter – gatherer culture is evident from the stone tools, grinding and pounding artifacts found among ancient campsites throughout the region. The Native Americans are thought to have used fire to influence the movement of bison, enticing them onto fresh, tender regrowth of herbaceous vegetation. This facilitated harvesting bison by nomadic tribes of Native Americans whose whole culture and customs relied on the ebb and flow of the migrating herds of bison.

This reference plant community is dominated by tall and midgrasses with a good perennial forb population. This community can be described as a Tall/Midgrass Dominant Community (1.). There is a moderate amount of sand sagebrush (Artemisia filifolia), skunkbush sumac (Rhus aromatica), yucca (Yucca glauca) and catclaw mimosa (Mimosa aculeaticarpa var. biuncifera). Scattered trees are present, mainly hackberry (Celtis spp.), Western soapberry (Sapindus saponaria) and Havard or sand shinnery oak (Quercus havardii). Woody plants make up approximately 10 – 15% of the total vegetative production for the reference plant community of this site. The principal grass species are little bluestem (Schizachyrium scoparium) and sideoats grama (Bouteloua curtipendula), with lesser amounts of sand bluestem (Andropogon hallii), Indiangrass (Sorghastrum nutans), sand lovegrass (Eragrostis trichodes), switchgrass (Panicum virgatum), dropseeds (Sporobolus spp.), silver bluestem (Bothriochloa laguroides) and Arizona cottontop (Digitaria californica). Cool-season grasses such as Texas bluegrass (Poa arachnifera), Canada wildrye (Elymus canadensis) and Needle-and-Thread (Hesperostipa comata) may be present. A diverse population of forbs such as Illinois bundleflower (Desmanthus illinoensis), dotted gayfeather (Liatris punctata), wild buckwheat (Eriogonum spp.), Western ragweed (Ambrosia psilostachya), spectaclepod (Dimorphocarpa wislizeni), sandlily (Mentzelia stricta), catclaw sensitivebriar (Mimosa nuttallii), prairie clover (Dalea spp.), erect dayflower (Commelina erecta), prairie sagewort (Artemisia caudata) and Queens delight (Stillingia sylvatica) compose 5 to 10% of the total vegetative production. In years of greater rainfall, cryptogrammic crust may be found. In advanced ecological states, this site is diverse and productive. Native trees such as western soapberry and hackberry may be present on areas with more favorable plant/soil moisture conditions. The community can be maintained by management practices such as prescribed grazing and prescribed burning.

It is thought that fire has historically played a role in sustaining the balance of the woody plants and tallgrasses. Tallgrasses such as sand and little bluestem and midgrasses such as sideoats grama are stimulated by fire and vegetatively respond well to periodic burns, especially if the burns are in spring or early summer. Woody shrubs are suppressed allowing grasses to become more dominant, allowing a grassland aspect to exist. Fire promoted diversity in the community allowing forbs to express themselves more in seasons following burning. An ecological balance between the woody plants, grasses, forbs and herbivores existed prior to the advent of European exploitation and settlement in the latter part of the 19th century. Its culture of fire suppression and abusive grazing began to alter the community allowing woody species to increase along with invading grasses and forbs. The reference community is dynamic, fluctuating between plant communities comprising 70 to 75 % grasses and shrubs like sand sagebrush and sand shinnery oak at 10 to 15% to a 60 to 70% grass and forb composition due to the normal cycle of climate extremes and presence of fire.

The observer needs to be cognizant of the weather patterns and fire frequency when observing this community and state. Many species have either increased or decreased, depending on herbivory and grazing management. There is general agreement that overuse, either by grazing or browsing is a major factor in retrogression and species shift resulting in the decline of palatable plants. With heavy continuous grazing by domestic livestock, the taller grasses are pressured and begin to decline in composition and production. When this grazing regime occurs, the Mid/Tallgrass Dominant Community (1.2) develops and midgrasses such as sideoats grama, sand lovegrass, silver bluestem, Arizona cottontop and perennial three-awns (Aristida spp.) increase along with annual forbs. Sand sagebrush, Havard oak, yucca, prickly pear (Opuntia spp.), and annual forbs, although present in reference condition, can increase and dominate with continuous heavy grazing, the absence of fire and brush management.

With heavy continuous grazing and fire suppression, the tallgrasses decline in response and the Midgrass/Shrub Community (2.1) exists. Midgrasses such as sideoats grama and sand dropseed (Sporobolus cryptandrus) increase along with forbs such as western ragweed. Woody shrubs such as sand sagebrush and Havard or sand shinnery oak increase to more than 25% of the annual forage production. Annual wild buckwheat, for example, and weak perennial grasses such as red lovegrass (Eragrostis secundiflora) and gummy lovegrass (Eragrostis curtipedicellata) can increase with heavy continuous grazing. In addition, there is a decrease of ground cover, decreased annual herbaceous production, and decreased vigor of tallgrasses such as little bluestem with heavy continuous grazing and fire suppression. Prescribed burning along with brush management may be necessary to restore and maintain the balanced plant community. The Loamy Sand ecological site responds well to brush management and individual plant treatment (IPT) using herbicides. Oaks and sagebrush can be successfully managed and the tallgrasses such as the bluestems and desirable midgrasses respond quickly to the reduction in competition for water and nutrients. Grazing deferment after brush treatment is essential to allow desirable vegetation to recover.

The Loamy Sand site retrogresses further with continued heavy grazing. If abusive grazing takes place after the woody plants have been suppressed, then the community can retrogress to the Midgrass/Shortgrass/Forb (3.1) community. This community is dominated by forbs, mainly western ragweed, camphorweed (Heterotheca subaxillaris) and annuals such as wild buckwheat. Scattered perennial grasses exist, mostly perennial threeawn, some dropseeds, fringed signalgrass (Urochloa ciliatissima), blue grama (Bouteloua gracilis), hairy grama (Bouteloua hirsuta), buffalograss (Bouteloua dactyloides) and weak perennials such as red lovegrass, gummy lovegrass and sandbur (Cenchrus incertus). Woody shrubs compose approximately 25%. Some scattered honey mesquite (Prosopis glandulosa) and prickly pear may increase in the less sandy portions of this site with sand sagebrush and Havard oak comprising most of the shrub population. Bare ground can increase soil movement that occurs when winds deposit sandy topsoil on any herbaceous or structural barrier. Sandy knolls and subsequent blowouts occur in advanced retrogressive states. Prescribed grazing, brush management, and management of weedy competition are essential in achieving any level of restoration.

A stable state of shrub domination can occur with sand sagebrush being the dominant species. If brush management is not initiated and heavy continuous grazing continues when community 2.1 is in retrogression, this site becomes a Shrub/Shortgrass Community (4.1). Decreased plant diversity is evident and is dominated by sand sagebrush mixed with Havard oak that may exceed 45% canopy. In this state, few perennial grasses such as fringed signalgrass, hairy grama exists and annual forbs, such as annual wild buckwheat, are very prevalent. Some pedestalling is apparent, water flow patterns are mostly absent, and wind transports and deposits soil on sand shinnery oak motts prone to blowout and the development of a hummocky landscape.

Communities 3.1 and 4.1 shows markedly decreased annual production with less biomass and organic matter forming. These communities respond well when prescribed grazing, brush management and deferment from grazing are implemented. Generally, range planting is not necessary to restore this site from regression. Usually there is enough tallgrass and midgrass seed sources and basal crowns present for a progressive response if competition from brush encroachment and grazing pressure is managed. To maintain a balanced plant community, occasional brush suppression may be necessary.

Plant Communities and Transitional Pathways (diagram):
The following diagram shows plant communities and transitional pathways that the vegetation on this site might follow. There may be other states not shown on the diagram. This information is intended to show what might happen with a given set of natural or man induced circumstances and 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.