By C. Wayne Hanselka, associate department head, professor and Extension program leader for Rangeland Ecology and Management, Texas A&M University

The structure and function of the ecosystem are the two main factors which determine rangeland health.

Structure refers to the soil and vegetation characteristics. Function refers to the ecological processes that drive the system, such as water cycles, energy capture and transfer, nutrient cycling and vegetative dynamics. These factors were discussed in my article in the February 2003 issue of The Cattleman.

When soil, vegetation, water, air and ecological processes are balanced, sustained and functioning, then rangelands are classified as "healthy".

However, when shifts in plant composition occur, whether caused by decreases of perennial species, increases in bare ground, or increases in weed or brush species, the rangeland is classified as "at-risk".

At-risk rangelands have increased erosion and less water infiltration due to inefficient water cycles and dysfunctional energy and nutrient cycles.

As degradation continues, the system can’t support large amounts perennial grass. As these grasses die out bare ground increases. This allows increased erosion and the establishment of annual grasses or herbaceous plants and shrubs.

Rangeland in this "unhealthy" category may continue to degrade until all the topsoil is gone; until ecological processes are completely dysfunctional; and until most of its productivity is lost. This is called desertification.

Figure 1. Drought interacts with human activity to desertify rangelands. (Photo by Allan McGinty)

Native grass hay fed to cattle can contribute to restoring healthy rangeland.

Desertification has been defined as the degradation of the land in arid, semi-arid and sub-humid regions as a result of human activities. Periodic drought interacts with improper grazing, burning, wood cutting, plowing, etc., to disrupt ecological function and change the structure of the system (Figure 1).

As desertification proceeds and rangeland health declines, certain at-risk warning signs become apparent. Corrective measures may be taken at the first warning signs and these measures are usually very effective and inexpensive.

However, as degradation continues into the unhealthy category, reversing the trend is usually very expensive and risky.

Generally, due to changes in the system, even if unhealthy rangelands are restored to the healthy category, they are not as productive as those rangelands which have been continually maintained in a healthy state. While restoration can improve range condition, the original health of rangelands should be carefully managed to product productivity.

All rangelands should be systematically and frequently monitored to record trends in structure and function. Reading your landscape will indicate if current management, under current conditions, is maintaining or improving the land.

If the land is healthy, and monitoring consistently shows it to be healthy, then no changes in management are warranted.

If the warning line between the healthy and at-risk categories is crossed, then management adjustments should be made.

Generally, management tools that affect the ecological processes are best suited for this purpose. Some of the most commonly used repair mechanisms for damaged rangelands include grazing management, weed and brush management, water conservation practices and reseeding.

Figure 2. Proper grazing can restore "at-risk" rangelands back to a "healthy" state.

Livestock grazing should be closely examined for timing, intensity, frequency and distribution. (Figure 2). Each of these grazing characteristics affect the soil surface, litter cover,

vegetative composition, nutrient turnover, energy capture and water cycling.

Livestock activity affects the land in several ways, such as physical impacts on the soil, breaking dead and undecayed vegetation, inputting manure and urine, affecting the vegetation through leaf and stem removal and contributing to system function and structure.

The health and vigor of individual plants are also affected. If grazed too early, too heavily, or too frequently, the plant’s carbohydrate manufacture and storage declines as does production of top growth and roots.

Control of grazing intensity will depend on the number of animals per unit area (stocking rate), number of animals in the pasture (stock density) and the length of time the stock are in the pasture.

Conservative to moderate grazing intensities are usually recommended (30 to 45 percent of the plant removed). It is difficult to judge the percentage of a plant that has been removed. It is easier to evaluate the amount of residue and stubble which remain.

Research and experience have shown for tall bunch grasses (big bluestem, yellow indiangrass, switchgrass, etc.) 1,200 to 1,500 pounds per acre of stubble should be left on the ground at all times. Midgrasses, such as little bluestem and buffel grass, require 750 to1,000 pounds per acre and sod grasses such as buffalo grass, curly mesquite and bermuda grass need 300 to 500 pounds per acre.

[Editor’s note: To learn how to evaluate residue and stubble pounds per acre read "How much forage do you have?" by Larry White and Calvin Richardson, Extension publication E-151. Find it online at http://tcebookstore.org/pubs/E151.pdf.]

This residue allows enough carbohydrate manufacture and storage to occur to keep the plant functioning, maintain growth and activity and allow a strong root system.

It also leaves an organic matter cover on the soil as protection from rainfall and moderate temperatures.

Some plants will be more heavily used than others for a variety of reasons, so the residual threshold recommendation is complicated by the frequency that livestock bite the plant.

If a plant is bitten again before it has had a chance to regrow, the plant is weakened. Control of grazing frequency is achieved through the use of a rest-rotation strategy using multiple pastures and either multiple or single herds.

Enough intensity should be placed on the pasture to ensure good grazing distribution over the pasture and to exert pressure on a variety of forage plants. The pasture should then be rested for a sufficient period to allow regrowth to occur.

In some cases grazing management alone will not achieve the level of improvement needed. The lack of plant diversity or dominance by a less desirable species may have long-term ramifications and brush or weed management may be necessary.

Decisions concerning the use of weed and brush treatments should be based upon long-term goals, characteristics of the problem, appropriate resources, available technology and economics.

Whether to use mechanical, chemical, biological or fire methodologies will depend upon considerations of safety, effectiveness and economics. Likewise, whether to use broadcast or individual plant treatments will depend upon density of the stand as well as other characteristics of the brush or weeds.

At-risk and unhealthy rangelands most often have damaged and ineffective water cycles. Rainfall tends to run off because of compacted or crusted soils and surface evaporation is high. Consequently, the land may be in a continual state of drought in spite of adequate rainfall.

There are several mechanical and biological methods that are useful to improve this situation. The use of raised contours has long been used in farming to retain water on the land and allow it to infiltrate into the soil.

Contour furrowing and plowing and throwing up a shallow berm, in strips, create mini-watersheds that concentrate water on a smaller area, thereby increasing the water received. On compacted soils, single or multiple shank rippers or subsoilers can be used to break up surface crusts and subsurface compaction. Seeding may or may not be a component of these methods.

Another method is one that combines several rangeland restoration components. Hay spread perpendicular to a slope will trap, slow and stop overland flow of water allowing more infiltration to occur.

If harvested late in the season, native or introduced grass hays may contain grass seeds or, in the case of coastal bermuda grass, grass seeds may be spread over the area prior to unrolling the hay bale.

If cattle are allowed access to the hay, the uneaten residue will be trampled into the soil adding organic matter, breaking surface crusts and enriching the mix with manure and urine while planting the grass seeds. This method has been successfully used with several native grass species including tanglehead, plains bristlegrass and little bluestem.

It is important to identify the state of rangeland health on a continuing basis. If deterioration continues, rangelands become more difficult and expensive to repair and restore. It may be impossible to restore the rangeland to its original condition; therefore, efforts should always be concerned with restoring rangeland ecological functions so the systems can self-regenerate and are self-sustaining.