- Basic principles of grazing management - the cornerstone of veld management systems
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BASIC PRINCIPLES OF GRAZING MANAGEMENT - the cornerstone of veld management systems
BEFORE any farmer can become a proficient manager of veld, he must acquire an understanding of the basic principles governing plant life, says Mr Charlie Donaldson, Head of Pasture Research at Grootfontein.
Mr Donaldson gives the assurance that a permanent, economic and practical solution to the problem of veld deterioration and low animal production can be obtained by applying veld management practices that are based on the fundamental ecological and physiological principles of the veld.
He explains that ecological principles concern all the factors, which influence the plant within its environment, while physiological principles relate to the growth and development of the plant.
Mr Donaldson points out that the grazing potential of each veld unit depends primarily on the combination of prevailing climatic and edaphic factors. It is only within the framework of these natural controls that the farmer can manipulate and influence the productivity, vigour and nutritional value of the natural veld.
Ecological Principles of Veld Management
The progressive development of the different plant communities in waves is known as plant succession. Waves of pioneer plants continue to increase and spread until a final stage or climax is reached.
Here is a step-by-step account of what happens during the development of veld from the pioneer to the climax stage:
the soil develops and improves.
the height, amount and diversity of the plant growth strata increase.
plant productivity increases and its own microclimate develops.
protection for the soil and animals increases.
plant diversity increases.
the tempo of change decreases with the advancement of succession.
the relative stability of the plant community increases.
At the climax stage a delicate balance exists between the plant community and the prevailing environmental factors, says Mr Donaldson. Stress factors like overgrazing or prolonged droughts will therefore trigger-off retrogressive succession resulting in the development of lower successional stages such as the sub-climax or pioneer stages. The removal of the unfavourable stress factor will again result in the continuation of progressive succession.
He points out that the tempo of veld improvement will largely depend on the nature and intensity of the stress factor and the species composition before and immediately after interference by this factor.
The successional stage of veld is determined by specific plant species (referred to as indicator plants) occurring in it.
Within each major ecological area it is therefore possible to identify plants that are indicators of the climax, sub-climax and pioneer stages. Mr Donaldson gives examples of the most important indicator plant species for the eastern mixed Karooveld in Fig 1.
He says that the plants in the sub-climax and pioneer stages are considerably poorer in dry matter production, perenniality, drought resistance and soil conservation properties than the plants in the climax stage.
A primary requirement of veld in areas subjected to frequent droughts is the ability to resist such droughts. One of the main indicators of the ability of veld to resist drought is the relative abundance of climax grasses. According to Mr Donaldson it is an established fact that plant succession is the major ecological process responsible for the stability or deterioration of natural veld. The stage of plant succession in which veld occurs can to a large extent reflect the past treatment applied to the veld, what the veld is capable of producing and what management practices should be applied to maintain or improve the veld.
Physiological Principles of Veld Management
The physiological principles of veld management are based on four critical growth periods in the seasonal development of the grass plant, viz. initial growth, active growth, reserve storage and the dormant stage.
Mr Donaldson explains that carbohydrates and other reserve nutrients are stored in the stem bases and the roots of healthy plants. The plant draws on these reserves at the start of spring when initial growth takes place for the production of the first leaves. As the area of the leaves increases, their photosynthetic ability is increased to the extent that they are able to produce their own carbohydrates to supply energy for their growth. The rate of root development also increases as more and more leaves are formed) until a stage is reached where the aboveground parts are independent of the stored root reserves.
The manufactured growth substances (carbohydrates) are transported during the growing season to those parts of the plant where they are required for growth. During autumn, when the temperatures drop, growth rate slows down and the excess carbohydrates formed in the leaves are transported to the roots and stem bases for storage until the following spring.
These root reserves serve as energy substrate for the following processes
for active root growth, which takes place during this period, provided soil moisture and soil temperature are favourable.
for respiration in winter and for initial growth during spring
New growing points (primordia) are also formed during this growing period and vegetative growing points develop to the reproductive stage for seed production during the next season. During the winter period the plant is virtually dormant although growing point development and respiration continue to take place.
Healthy vigorous plants manufacture large amounts of nutrients for their own use and for storage. The stored reserves are thus available for the following processes: -
to ensure new growth after a drought.
for the production of new leaves during spring.
to ensure new re-growth after grazing by animals.
Any period of rapid growth leads to withdrawal of reserves, and severe defoliation at this stage will result in a serious depression of the growth rate of the plant. In fact, says Mr Donaldson, there are two threshold levels between which the foliage should be maintained: a lower level below which further defoliation will seriously affect the physiological processes in the plant and thus reduce production, and an upper level above which further resting will lead to relatively little increase in grazeable material and a decrease in quality.
He warns that continuous severe defoliation of the producing parts of the plant will result in the weakening of the plant and even death. Leaves are needed to produce leaves, he says.
Mr Donaldson stresses that all effective veld utilization systems are based on the principle of rotational grazing with the main objects of meeting the physiological growth requirements of the plants, for important ecological processes to take place and to meet the nutritional needs of the grazing animals.
Karoo Regional Newsletter Spring 1984