Longterm Degradation Patterns

The ability of the soil to store moisture and nutrients strongly influences the annual production potential of a site. If erosion significantly reduces topsoil depth, there is some danger that a self-generating cycle of degradation will begin, whereby grazing reduces the cover and organic matter on the site, resulting in less water and fewer nutrients being retained for use by plants. This also causes the microclimate to deteriorate, leading to a decrease in soil-enhancing microorganism activity and a harsher environment for germination. In such a situation, plant density is reduced and less forage is produced, leading to the remaining plants receiving greater focus by grazing animals. These factors further accelerate runoff and erosion. This can eventually lead to the diminution or destruction of the biological production potential of the land and can also reduce the potential magnitude of future benefits associated with introduction of improved livestock breeds or technological innovation.[7]

One way in which loss of biological production potential is frequently manifest is in the context of a drought paradox: Ranchers perceive that drought frequency and severity have increased over time, but the climatic data show no significant change in long-term precipitation amount or pattern. This apparent paradox can often be attributed to erosion and the concomitant loss of soil moisture storage capacity, which results in the remaining topsoil drying out sooner and more frequently.1-8-1 The risk of grazing practices interacting with drought to accelerate erosion is often increased because of the lag time associated with destocking in response to the lower plant productivity/ livestock carrying capacity caused by the drought.

Soil loss cannot be effectively restored through management since topsoil formation occurs at the rate of 1 cm formed every 100 400 years. By the time a self-generating degradation cycle becomes obvious, it may be too late to implement economically viable conservation options. Early recognition of a developing degradation pattern requires knowledge of grazing land ecology because the first signs of an impending erosion problem almost invariably are manifest by changes in plant community characteristics and subtle changes in surface soil structure.1-7'9-1

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