Water has always been a major limiting factor on Texas rangelands. Every drought reminds us that forage production is not guaranteed every year and that management must be prepared for the inevitable forage shortfall even if livestock are properly stocked for the normal year. While the amount and timing of rainfall are important, the productivity of rangeland is more closely tied to the amount of soil moisture captured when it does rain. A land manager’s current and past management practices are what determine how much rainfall penetrates the soil, the kinds of plants on your land and the amount of runoff, sediment and non-point pollutants that leave a property.
Factors that affect where rainfall goes are the type and density of vegetative cover; the intensity of a storm; the amount of moisture in the soil before the storm; the capacity of the soil to hold water; and the slope of the land. These factors affect how much moisture is retained by the soil and the amount lost to runoff or evaporation. If a manager correctly “reads” the condition of rangeland, he or she is better able to make timely management decisions to protect a ranch’s resources.
How do you determine pasture health? Knowing what to look for is the key to reading a landscape. Managers must monitor both current conditions and changes over time to determine if damage to the soil, plant communities and water resources is occurring; if past decisions are producing expected results; and whether management should be changed to correct problems before they become critical.
The first indicator of range or pasture health is vegetative cover: both the amount of vegetation and the species composition. Good vegetative cover, with little bare ground, slows the movement of water across the land and lessens the impact of raindrops on the soil surface. The greater the raindrop impact and the faster the water moves, the more soil will be dislodged and carried away. The slower the movement of water surface water, the more time there is for it to soak into the soil.
A certain amount of vegetative cover should be left ungrazed at all times. This is called the threshold residue. It varies with plant species, soil type and climate, and it determines the amount of rainfall captured and the potential for future grass production. The management tool is to adjust livestock stocking rate seasonally so that the threshold residue is not removed.
The kinds (species) and classes (grasses, forbs, etc.) of plants determine the amount of rainfall that will be intercepted by foliage and evaporate back to the atmosphere, or that will reach the soil surface. Being able to identify these plants is very important. Monitoring plants with photo points can help document seasonal and annual changes in the landscape and pinpoint problem locations.
The second indicator of landscape health is the soil surface. Large areas of bare ground, pedestaled plants, litter dams, rills and gullies are signs that rainfall is running off the land rather than infiltrating the soil. Another danger sign is stream bank erosion, which often occurs when riparian vegetation (the vegetation along rivers and streams) is inadequate to stabilize the bank against flowing water. Riparian vegetation is important for maintaining natural stream channels. Closely checking stream bank stability and riparian zone vegetation can help a producer recognize a problem with the land upstream.
The take home message here is to know what is happening on your land. Check for signs of increasing bare ground, reduced litter, lower forage production, changing plant species and stream bank erosion. These signs tell you that rainfall is not being effectively captured and that sediment losses are reducing the soil’s productivity and water-holding capacity. Learning to read your landscape will pay off in greater productivity now and sustainable productivity in the future.