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Agricultural and forestry biodiversity
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Pine plantations,
vineyards,
wheat fields and
fragments of natural vegetation near Swellendam, Western Cape. [photo H.
Robertson, Iziko ©] |
Agricultural land takes up more of the land surface of
southern Africa than any other type of landuse and holds a vast diversity of
life, ranging from pests and associated organisms in cultivated lands through to
natural vegetation containing rare and endemic species that need protection.
Farmers have a critical role to play in the conservation of indigenous
biodiversity in southern Africa. Many are willing to manage their farms in a
conservation-friendly fashion, once they understand the special habitats they
are fortunate enough to have on their farms. Increasingly, farmers are exploiting the
natural splendour of their farms through developing a tourism component to their
farming strategy. This strategy has often extended to turning the farm back into
a natural area and amalgamating it with adjacent farms to form large game farms
for tourism.
Biodiversity components in agricultural systems
Cultivated crops
Cultivated crops are usually monocultures in that only one plant species is
cultivated. However, there are many species in such so-called monocultures
including weeds and their associated organisms that compete with the crop
species for resources, pollinators, crop
pests (insects, mites,
nematode worms, birds, plant pathogens, etc), predators and parasites that attack the pests, and other
organisms not directly associated with the crop that are able to exist in
this disturbed system (e.g. ground dwelling species such as carabid
beetles and springtails). For an example of the range of crop pests found on
a single crop species, see
pests of maize.
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Cultivated pastures
Cultivated pastures include lucerne (Medicago
sativa),
Kikuyu grass (Pennisetum clandestinum), and
Stipagrostis grasses. These are grown for grazing animals like
sheep and cows. For instance dairy farms in the foothills of the Drakensberg
in KwaZulu-Natal typically graze their cows on a combination of natural
grasslands, kikuyu, maize and Stipagrostis pastures. Cultivated
pastures are not ploughed regularly like fields for annual crops so
communities of organisms have a chance to build up in these pastures. |
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Fallow fields
Fallow fields have an abundance of weedy plants species
with all their attendant herbivores, pollinators and other associated
organisms. |
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Fruit orchards
There are distinct communities of insects and other
organisms associated with particular fruit tree species. Total reliance on
pesticides to kill pests has been found to be uneconomic and environmentally
unsound because the pesticides kill the parasitoids and predators that kill
the pests. Fruit farmers instead aim for integrated control where they
manage their orchards in a way that promotes the predators and parasitoids
and they only use pesticides selectively. Honeybees (Apis mellifera)
are essential to fruit production because they pollinate the flowers, thus
enabling the ovary in each flower to develop into a fruit. Bee hives are
brought into the orchards during flowering to promote maximum pollination. |
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Plantations
The two main types of plantations cultivated in South
Africa are pines and
eucalypts. The wood from plantations is used for timber
(especially props for mines) and paper production. Besides companies like
Sappi and Mondi that own large areas of land and plant thousands of hectares
of trees, there are farmers who have opted for turning parts of their farms
into plantations. This is a long-term investment because it takes 15-20
years before the plantation is harvested. There are a number of pests of
pine and eucalypt and in addition the plantation creates a forest
environment that can create habitat for some indigenous organisms such as
many of the leaf-litter inhabiting species. |
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Domesticated animals
Biodiversity associated with domesticated animals includes the parasites
that live in and on these animals, beneficial microorganisms that live in
the gut, and invertebrates that are associated with dung. |
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Natural vegetation
Most farms in southern Africa have at least some natural vegetation. In many
cases, such as livestock farms in the karoo and grassland regions, most of
the farm consists of natural vegetation that is used for grazing. The skill
of the farmer is in managing these natural grazing systems in a sustainable
manner. Other farms consist mainly of cultivated land but do have patches of
natural vegetation left, mainly around rocky outcrops that can't be
ploughed, or along road verges, or in and around wetlands. Farms play a very
important role in conserving the natural biodiversity of southern Africa.
The natural vegetation on farms needs to be managed for both sustainable
utilisation and in a way that conserves the natural biodiversity. |
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Farmyard
The farmyard has its own special biodiversity such as the trees grown for
shade (e.g. Eucalyptus), flowering plants grown in the garden and along driveways, and the
birds that nest under the eaves of buildings. |
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Wetlands
Farming often results in the modification of wetlands, which can seriously
affect the indigenous animals and plants existing in these systems. For instance,
Wattled cranes in the foothills of the Drakensberg in KwaZulu-Natal have
been seriously reduced in numbers from the modification of wetlands in
grasslands. Farms often have wetlands that contain rare and endangered
species and thus farmers need to manage these systems in a way that sustains
these species. In addition to natural wetlands, there are farm dams that
despite being artificially constructed can act as suitable
habitats for many indigenous species, such as waterbirds. |
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Transition zones
Transition zones are disturbed habitats along borders, such as road verges
and often have species not commonly found elsewhere on the farm. |
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Text by Hamish Robertson |