Dr. Don Ball
The dictionary defines ecology as the area of science dealing with the inter-relationship of organisms and their environment. As compared to other types of agricultural production, pasture ecology is particularly interesting and complex because it involves animals, plants, soil, and the many climatic and environmental factors that affect them.
As indicated by the previous four articles in this series on pasture ecology, many factors affect plant growth and survival. Since a given factor varies in intensity over time, pastures are extremely dynamic. Given the numerous influences that impact upon pasture plants, often only a slight difference in degree of a particular influence, in combination with other factors, may make the difference between survival and death of an individual pasture plant.
In a well-managed pasture, the practices imposed by the livestock producer should be the factors that "tip the balance" in favor of desirable species and reduce negative influences. Most pastures were planted by a pasture manager and thereafter the stocking rate, the grazing system used, the extent of application of lime and fertilizer, applications of pesticides, as well as weather conditions have major effects on pasture composition and productivity.
Collectively, even minor influences can have important long-range effects. In many cases, factors interact with each other, thus compounding the effects. For example, if root growth of a seedling grass stand is poor due to inadequate fertilization, later drought stress may be more damaging than it otherwise would have been. Weakened plants not killed by the drought may be more susceptible to disease. Overgrazing may further limit root growth, with the ultimate result being death of plants.
In some cases, one influencing factor can offset another. As an example, tall fescue is not well adapted near the Gulf Coast due to high stress related to droughty soils, heat and nematodes. Yet, in some low-lying wet-natured fields in this area, it can persist well with proper management.
Ecology is really simply the study of influences within a biological system. In any given situation, some influences are stronger or more important than others. Sometimes a single influence is of overwhelming importance, but more frequently, plant population or species composition changes within a biological system are the result of a set of influences that have had a collective effect.
Most factors that have influences in pastures can themselves be offset by management imposed by a livestock producer. Thus, whether a producer realizes it or not, he or she plays a critically important role in pasture ecology. Many factors come into play, but ultimately the responsibility for the appearance and productivity of a pasture lies with the manager.
Don Ball is an Extension Forage Crop Agronomist with Auburn University.