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Agricultural and forestry biodiversity

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.

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. 

Fallow fields

Fallow fields have an abundance of weedy plants species with all their attendant herbivores, pollinators and other associated organisms.

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. 

 

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. 

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.

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.

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.

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.

Transition zones

Transition zones are disturbed habitats along borders, such as road verges and often have species not commonly found elsewhere on the farm.

 

Text by Hamish Robertson


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