the vegetation types and veld condition - Maremani Nature Reserve

Introduction
CHAPTER 6
VELD CONDITION AND ECONOMIC CARRYING CAPACITY
Maremani is representative of the Mopane Bushveld and the grazing can be considered as sweet veld.
Veld condition as well as the carrying capacity of the area in general, will vary from season to season,
depending mainly on the rainfall, and also to a certain extent on past and present utilization. Each of the
recognised plant communities is associated with a specific habitat, has its own diagnostic species
composition, and therefore also has its own grazing and browsing potential and economic and ecological
carrying capacity.
The concepts of economic and ecological carrying capacities need to be explained. Game numbers
will increase from an initial low to a level where the available food, water and shelter resources become
limiting (Caughley 1977). Numbers increase slowly at first and once a critical stage is reached, the growth
rate is exponential and numbers increase rapidly. At a certain upper level, density-dependent factors such
as competition for resources, lower fecundity and increased mortalities result in a leveling-off of population
growth to a point where births equal deaths, and net growth (or yield) is zero. In practice, the ultimate
population density fluctuates around a fluctuating upper level, which arises from, for example, variations in
rainfall, inter-specific competition, predator-prey relations or accidental fires. The level around which the
population oscillates is known as the ecological carrying capacity. It is the population level that is likely
to exist in unmanaged large natural areas. Fluctuations in numbers can be quite dramatic, with severe
crashes occurring during periods of prolonged drought or disease epidemics. Allowing certain species to
attain high densities may impact negatively on other more sensitive species. Therefore, should the
management objective be to increase species diversity, the numbers of aggressively competitive species
need to be controlled.
If a population is maintained below the ecological carrying capacity by cropping, the net growth of the
population is positive, as there is room for expansion in the form of resource abundance. The population
is then at an economic carrying capacity. There is no one single economic carrying capacity but there is
a point at which maximum sustained yield (MSY) is obtained, usually around 70 to 80% of the ecological
carrying capacity.
Different equations have been proposed to calculate carrying capacity of an area. In general, by
combining an ecological or veld condition index, the grass production and/or canopy cover, rainfall, the
incidence of fire, accessibility of the terrain, grazing habits and social behaviour of animal species, it is
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