UNITS

• OVERVIEW
• Unit 1 Importance of plants in agriculture
• Unit 2 Field crops
• Unit 3 Horticultural crops 
• Unit 4 Fodder crops 
• Unit 5 Forests
• Topic questions

TOPIC 6: PLANT STUDIES

Overview

What you will cover in Topic 6

Unit 1: Importance of Plants in Agriculture

1.1 Volume of agricultural production
Due to the aridity of land in South Africa, only 13,5% can be used for crop production, and only 3% is considered high potential land.

• But South Africa has a large agricultural sector = net exporter of farming products.
• Biggest exports = sugar, grapes, citrus, nectarines, wine and deciduous fruit.
  • Agricultural exports = 8% of South African total exports for the past five years.
  • Almost 1 000 agricultural cooperatives and agribusinesses in South Africa.
  • Agricultural industry contributes around 10% of formal employment (low compared to other parts of Africa) and provides work for casual labourers.
  • It contributes around 2,6% of the GDP.
  • South Africa is the eighth largest wine producer in the world, and the eleventh largest producer of sunflower seed.
  • The largest locally produced crop is maize, and it has been estimated that 9 million tons are produced every year, with 7,4 million tons being consumed.
• The gross value of agricultural production is determined by the quantity produced and prices received by producers.
• In these terms, the largest contributors towards the gross value of field crops for the past five seasons are:
  • maize (48,6%)
  • sugar cane (14,2%)
  • wheat (12,5%)
  • sunflower seed (6,7%)
  • hay (6,0%).

1.1.1 Maize

• In 2009/10:
  • South Africa had the largest commercial maize crop in 29 years, around 13,0 million tons (an increase of 8,2 tons compared to 2008/9)
  • The estimated area that producers planted is 2,742 million ha:
    • Commercial white maize planting : 1 719 700 ha = an increase of 15,5% compared to 2008/9
    • Commercial yellow maize plantings: 1 022 700 ha = an increase of 9,0% compared to 2008/9.
• The average annual gross value of maize for the period 2004/5–2009/10 is R14 041 million.

1.1.2 Wheat
In terms of value of production, wheat is the second most important field crop produced in South Africa.

• In the 2009/10 season, this crop contributed approximately 11% to the gross value of field crops.
• The average annual gross value of wheat for the past five years up to 2009/10 amounts to R3 619 million, compared to R14 041 million for maize, which is the most important field crop.
• The estimated area planted to wheat for the 2010 season is 558 100 ha, which is 13,1% less than the 642 500 ha of the previous season.
  • Of this area, 265 000 ha (47%) are in the Western Cape and 204 000 ha (37%) are in the Free State.
  • According to producers, the decrease in plantings can be attributed mainly to the relatively low producer prices of wheat.

1.1.3 Sorghum
Sorghum is the third most important grain crop (after maize and wheat), but it contributes only a small percentage to the total domestic grain crops.

• For the past five seasons, South Africa produced on average 212 700 tons of sorghum p.a. The estimated average annual gross value 2009/10 amounts to R363 million.
• During the 2009/10 production season (April to March):
  • produced mainly in the Free State (57,7%), followed by Mpumalanga and Limpopo (17,3% each) and the North West (6,3%).
  • An estimated 86 675 ha were planted, an increase of 1,4% compared with the 85 500 ha planted during 2008/09.
• Sorghum contributed approximately 1,3% to the gross value of field crops.

1.1.4 Sunflowers

• Commercial seed production during 2009/10 was approximately 516 265 tons, which is 35,6% lower than the previous season and 17,1% lower than the average of 622 600 tons for the previous 5 years.
• During the 2009/10 production season, the bulk of the crop was produced in the Free State (46%) and North West (37%) provinces.
• The contribution of sunflower seed to the gross value of field crops during the season is approximately 5,6%, compared to the 47,6% of maize.
  • The average annual estimated gross value of sunflower seed for the 5 years up to 2009/10 amounts to R1 934 million, compared to the R14 041 million for maize.

1.1.5 Soya beans

• Contributes about 4,9% to the gross value of field crops, and the estimated average annual gross value of soya beans for the past five seasons up to 2009/10 amounts to R106 million.
• The planting of soya beans = between 46 000–311 450 ha over the past 20 years.
• For two consecutive seasons, the area dedicated to soya-bean production has increased rapidly from an estimated 237 750 ha to an estimated 311 450 ha.

1.1.6 Cotton

• The area planted reached its peak during the 1987/88 production season, when an estimated 181 676 ha were planted. Since then, plantings have decreased substantially (e.g. total area planted the 2009/10 production season is estimated at 5 420 ha).
• The domestic production of cotton lint for the 2009/10 marketing season is estimated at 44 920 bales of 200 kg each, which is a drop of 8,5% from the 49 100 bales produced for 2008/09.
  • Lower cotton production means that more cotton lint will probably have to be imported.

1.1.7 Sugar cane
There are currently approximately 35 300 registered cane growers → produce on average approximately 20 million tons of sugar cane a year in areas extending from the Eastern Cape Province, through KwaZulu-Natal to Mpumalanga.

• Large-scale growers are responsible for approximately 85% of the total sugar cane production, while 8,4% of the total crop is produced by small-scale farmers and 6,5% by milling companies.
• The South African sugar industry produces an average of approximately 2,2 million tons of sugar per season.

1.2 Importance of plants
1.2.1 Economic importance of agriculture

• In monetary terms, agriculture is less important to our economy than mining and secondary industries:
  • In 1930 agriculture contributed about 30% of the GDP
  • In 1960 = 11,1%
  • In 1999 = 5%.
• Despite this decline, the farming industry remains vital to the economy, development, and stability of the southern African region.
  • The various sectors of the industry employ approximately one million people, or 8% of the workforce.
• Primary agriculture currently contributes about 3% to the GDP of South Africa.
  • However, there are strong linkages into the economy, so that the agro-industrial sector comprises about 7% of GDP.
• The total contribution of agriculture to the economy increased from R38 billion in 2002 to R68 billion in 2008.
  • The total gross value of agricultural production for 2007/08 = R199 billion.
  • Of this, over R65 billion came from field crops and horticulture, as shown in the table on the next page.

Total gross value of field crops and horticulture production for 2007/08

1.2.2 Other reasons why plants are important

• Oxygen is a by-product of photosynthesis that takes place in plants.
• Most of the food that we eat comes from plants.
• Many plants are used as medicines: 80%–85% of all medicinal drugs originate in wild plants.
• Plants have aesthetic importance: decoration and aroma.
• Plant roots reduce runoff and increase the rate of water entry into the soil.
• The leaf canopy of plants, like trees and shrubs, breaks the impact of raindrops on the soil surface, and the roots of plants bind the soil to prevent soil erosion.
• Grasses are used for roofing in the rural areas. Wood is used for sculptural and carpentry designs.
• Plants are important for the resources they provide for commercial activities:
  • Fibres and cotton are made into cloths.
  • Wood used for buildings and furniture.
  • We get gums, pulp for paper and rubber.
  • Fuels and gases, like diesel and ethanol, are being made from plants.
• Plants are a source of fuel in the rural areas (wood for cooking fires). In addition, coal is obtained from decomposed plants that have been buried underground for millions of years.

1.3 Criteria for successful crop production
Crops include grain crops, root crops, vegetable crops, forestry crops and fodder crops. The table below indicates some of the criteria that should be followed for successful crop production.

Criteria for successful crop production

1.4 Classification of crops
Crop plants are classified into four categories:

• Field crops
• Horticultural crops
• Forestry crops
• Fodder crops.

Unit 2: Field Crops

2.1 The classification of field crops and their climatic and soil requirements

• Field crops can be classified into a number of categories, such as:
  • grain crops (maize, wheat and sorghum)
  • oil seed crops (sunflower and soya beans)
  • industrial crops (sugar cane and cotton).
• Field crops are usually grown commercially on a large scale, but are also cultivated by small-scale and subsistence farmers.
• The gross income from field crops increased from 2007 by 26,7% to R29 872 million for the year ended June 2008.

2.1.1 Grain crops

• The grain industry is one of the largest industries of South African agriculture, producing between 25% and 33% of the total gross value of agricultural production.
• The gross value of grain production is usually around R12 billion per annum.

Maize / corn (Zea maize)

• The largest locally produced field crop.
• Produced on large scale mainly in the North West, the Free State and Mpumalanga.
• Sun-loving:
  • it grows well in areas where there is no frost.
• It requires a well-drained loamy soil with a lot of nitrogen and potassium in the soil.
• Maize requires a well-distributed annual rainfall of between 450 mm and 900 mm.
• The staple food in many homes in South Africa: it can be eaten in many different ways:
  • fresh
  • processed: samp, maize rice and maize flour
  • manufactured: popcorn, corn flakes and biscuits.
  • porridge and breakfast cereals
  • alcoholic beverages, like mqombothi
  • corn oil, which is used for cooking oil, salad oil and margarine.
• White maize is the most important source of carbohydrate for human consumption.
  • Animals (e.g. fowls) are mostly fed with yellow maize because it is rich in both carbohydrates and Vitamin A.
  • Poultry animals (chickens) and livestock animals (pigs and cattle) are fed with feeds and concentrates that contain a high proportion of maize.

Wheat

• Produced mainly in the winter-rainfall areas of the Western Cape and the eastern parts of the Free State
• Wheat is more demanding with regard to soil, climatic conditions and water supply than other cereal crops. It requires heavy, deep, well-aerated soils, rich in humus, with a high water capacity and a pH between 5,5 and 7,5. Nutrient-rich clay and black earth soils are ideal. Wheat is sensitive to soil salinity.
• Uses of wheat include flour production for making pasta, bread and cakes; breakfast cereals; and the preparation of alcoholic beverages. The husks are given to livestock as a feed supplement and to pigs as a good source of vitamins

Sorghum

• One of the best examples of drought-tolerant grain crops. It does well under very hot and dry conditions. During drought, sorghum stays dormant and then continues to grow with the onset of the rains.
• Cultivated mostly in the drier parts of the summer-rainfall areas, such as Mpumalanga, the Free State, Limpopo and the North West.
• It is regarded as a sun-loving crop because it grows well under summer conditions.

2.1.2 Oil seed crops
Sunflower

• Grown for the seeds. Oil is obtained from matured seeds for:
  • edible cooking oil
  • soap, candles and margarine
  • the waste after the oil has been extracted is used for poultry-feed and livestock.
• South Africa is the world’s 12th largest producer of sunflower seed.
• Produced in the Free State, the North West, on the Mpumalanga Highveld and in Limpopo.
• Sunflower, compared to other crops, performs well under drought conditions and is very sensitive to waterlogging. Sunflower adapts relatively well to a wide variety of soil types.
• Traditionally, sunflower cultivation was limited to soils where the clay percentage varies between 15 and 55% (sandy loam to clay soil types). At present the major planting areas are in soils with a clay percentage of less than 20%.

Soya beans

• Mainly produced in Mpumalanga, the Free State and KwaZulu-Natal. Small quantities are produced in Limpopo, Gauteng and North West.
• Sun-loving; require temperature range of 21 to 27ºC for very successful seed set. An average rainfall distribution of 450 – 700 mm is required for optimum production.
• It does well on most soils and does not require soils rich in nitrogen for good yields.

2.1.3 Industrial crops
An industrial crop is grown to produce goods to be used in the production sector, rather than food for consumption.
Sugar cane

• South Africa is one of the world’s leading cost-effective producers of high-quality sugar. The industry includes the agricultural activities of sugar cane cultivation and the industrial factory production of raw and refined sugar, syrups and specialised sugars and a range of by-products.
• The sugar industry makes an important contribution to the national economy.
  • Direct employment within the sugar industry totals 85 000 jobs.
  • Direct and indirect employment is estimated at 350 000 jobs, including employment in rural areas.
  • The South African Cane Growers’ Association and the milling companies undertake development projects and are involved in Black Economic Empowerment (BEE) through a range of initiatives.
• For cultivation, sugar needs:
  • tropical/temperate climate = minimum 1 500 mm annual moisture.
  • fertile, nutrient-rich, sandy, alluvial or loamy soil that is well drained with an optimum soil pH of about 6,5. Excess nitrogen causes significant cane growth but lowers the sugar content of the plant.

Cotton

• Cultivated in Mpumalanga, Limpopo, the Northern Cape, KwaZulu-Natal and North West.
• Constitutes 74% of natural fibre and 42 % of all fibre processed in South Africa.
• The quantities of cotton lint for the 2006/2007 marketing year were:
  • Mpumalanga = 36 000 bales (1 bale = 200kg)
  • Limpopo = 12 332 bales
  • Northern Cape = 11 103 bales.
  • Eastern Cape = 132 bales of cotton lint.
• About 75% of local production is harvested by hand.
• Cotton is grown under irrigation as well as in dry land conditions.
• With a normal growing period of 200 days, the cotton plant requires:
  • Temperature:
    • A relatively high temperature over a long growing season; needs abundant sunshine especially from December to February. Adequate sunshine is necessary for boll production and maturation.
    • Temperatures under 20ºC have a slowing down effect on the growth of the plant, especially during the flowering and boll phases.
    • Low temperatures just after planting time (at germination) as well as low night temperatures during any stage of growing, are potentially harmful.
    • For good germination, seedbed soil temperature = at least 18ºC.
  • Water:
    • Cotton = a drought-tolerant plant that can provide relatively good yields under dryland conditions, even in areas where the rainfall is less than 500 mm annually.
    • For profitable, good quality yields, higher, evenly spread rainfall (about 500 mm to 1250 mm) is required.
    • Therefore, cotton in South Africa is mainly cultivated under irrigation.
  • Soil:
    • Performs best in deep, fertile, sandy loam soils with reasonable drainage.
    • Does not do well in sandy soils or heavy clay soils (clay soils present problems with the germination of seedlings).
    • Prefers a deep soil, one metre or more.
    • As cotton is very susceptible to waterlogged conditions, soils with poor drainage should be avoided.
    • Although cotton is relatively tolerant as far as pH is concerned, the best results are obtained with a pH of between 5,5 and 7,5. The plant is quite sensitive to aluminium poisoning and should therefore not be planted in soils with a pH value of below 5,5 (determined in water) where the aluminium concentration is high.
    • Has high tolerance to brackish soil.

Unit 3: Horticultural Crops

3.1 Classification of horticultural crops

Related Items

• Horticulture = scientific study and cultivation of fruits, vegetables, flowers and ornamental plants. Some of the areas in horticulture are:
  • Floriculture – the production and marketing of flowers and floral crops
  • Pomology – the production and marketing of fruits
  • Olericulture – the production and marketing of vegetables
  • Landscaping – the designing, production and marketing of landscape plants
  • Post-harvest physiology – maintaining the quality of horticultural products and preventing them from spoiling
  • Viticulture – the production and marketing of grapes
  • Oenology – all aspects of wine-making
  • Arboriculture – the study of trees, vines and shrubs
• Plant agriculture is divided into:
  • agronomy (herbaceous field crops, mainly grains, forages, oilseeds and fibre crops)
  • forestry (forest trees and products)
  • horticulture: edibles (garden crops, particularly fruits, vegetables, spices and herbs) and ornamentals (highly perishable because they are utilised in the living state, with water essential to quality)
• Fruit crops are cultivated for their fruit. Trees or shrubs bearing nuts are often treated as a special category of fruit crops.
• Vegetable crops are commonly herbaceous plants grown as annuals or biennials and occasionally as perennials that have edible parts (including, confusingly, the botanical fruit). Examples of edible parts include the root (sweet potato), tuber (potato), young shoot (asparagus), leaf (spinach), flower buds (cauliflower), fruit (tomato), and seed (pea).
  • Plants grown for ornamental use (e.g. cut flowers, bedding plants, interior foliage plants or landscape plants) = big group = thousands of species.

3.1.1 Economic importance of horticultural crops
The floriculture industry employs about 17 500 people.

• There is a strong demand for South African floriculture products and markets worldwide (e.g. Germany, the United Kingdom, Japan and the Netherlands).
• In the local market, many people retail different kinds of flowers, fruits and vegetables for their daily income. Some of these people set up stalls along the roadside to sell their vegetables.
• South Africa = main exporter of protea cut flowers = more than half of the proteas sold on the world market. South African proteas and Cape greens, whose cultivation is mainly concentrated in the Western Cape, are marketed in Europe.

3.2 The classification of vegetables and their basic climatic and soil requirements
The table below summarises the classification of vegetables and their basic climatic and soil requirements.

The classification of vegetables and their basic climatic and soil requirements

3.3 The classification of fruits and their basic climatic and soil requirements
Fruits can be classified into:

• Tropical fruits (e.g. bananas)
• Subtropical fruits (e.g. avocados)
• Deciduous fruits (e.g. apples, grapes).

3.3.1 Tropical fruits (e.g. bananas)

• There are two broad types of bananas:
  • bananas that are eaten ripe (musa sapientum)
  • bananas that are cooked and eaten green or fried in oil when ripe (musa paradisiacal).
• Bananas grow well:
  • in the subtropical regions of Southern Africa
  • medium to high temperature ranges from 22 – 35ºC
  • an even rainfall distribution range of 95 – 105 mm per month
  • in a rich loamy soil with a lot of organic matter.
  • Mostly cultivated between Port Shepstone and Port Edward in KwaZulu-Natal.

3.3.2 Subtropical fruits (e.g. avocados)

• Climatic requirements:
  • warm (mean daily temperature range of 20 – 24oºC), moist and fairly humid conditions
  • an evenly distributed annual rainfall of 1 000 mm
  • in well-drained soil with about 20 – 30% clay.
  • Mostly cultivated in KwaZulu-Natal, Mpumalanga and Limpopo.

3.3.3 Deciduous fruits (e.g. apples and grapes)

• Deciduous fruits shed their leaves during a certain period of the year and may be scarce if not cultivated in greenhouses.
• Deciduous fruits require temperate conditions in which some months of the year are very cold and wet.
• The Western Cape and the Langloof Valley in the Eastern Cape: large-scale production of deciduous fruits, such as grapes, apples and pears.
• Plums, peaches and apricots are produced on a large scale on the highveld of Mpumalanga and in the eastern parts of the Free State.
• Apples do well in regions that do not experience very high temperatures.
  • They require well-aerated soils with good organic matter content.
  • Perfect conditions are a crumbly soil with medium fertility and slightly on the acid side. Extremes of acid or alkaline soil will need to be corrected before planting.
• Soil type so greatly influences the flavours and characteristic of grapes that grapes grown on neighbouring farms can have a different taste.
  • Generally, grapes require well-drained sandy loam soil. Grapes prefer cool winters with winter rainfall of about 750 mm per year to allow them to move into a desired state of dormancy.
  • They require moderate to warm summers to allow for ripening.

3.4 Flower crops

• Ornamental horticulture (floriculture) is the intensive production of flowers and ornamental shrubs and plants. A floriculturist grows flowers and a florist sells flowers and flower arrangements.
• The South African horticulture industry has the opportunity to develop into a significant player on the international market. The horticulture industry employs over 17 500 people.
• The main types of flower crops extensively used in South Africa are the fynbos, garden flowers and cut flowers.

3.4.1 Fynbos

• Major vegetation type of botanical region known as Cape Floral Kingdom. It is the smallest (90 000 km2) but richest (9 000 species) of the world’s six floral kingdoms. More than 6 000 species are endemic.
• Three main types of fynbos:
  • proteas: large with feathery leaves
  • restiose grasses
  • Ericas.
• Fynbos promotes agro-tourism.

Climate

• Mediterranean climate: cool wet winters and hot, dry summers.
• Resistant to strong coastal winds.
• Summer droughts, extremely poor, well-leached soil and intense fires every 4 to 20 years are necessary for the development of fynbos.

3.4.2 Garden flowers

• Grown for beauty and fragrance.
• Annuals (1 year); biennials (2 years) and perennials (evergreen and deciduous).

3.4.3 Cut flowers

• In demand because of beauty and fragrance; used for a variety of occasions.
• Commercially grown on farms for export, for retail to supermarkets and florists.
• Should be long-stemmed, fragrant and have good vase life.

3.5 Shrubs and indigenous crops
Shrubs are woody plants that have many small, leafy branches. Two indigenous shrubs have become important crops.

3.5.1 Rooibos (Aspalathus linearis)

• Endemic to South Africa. The Khoesan discovered that the tea has medicinal benefits.
• Naturally distributed in the winter rainfall area from about Van Rhynsdorp in the north to the Cape Peninsula and the Betty’s Bay area in the south. The area experiences cold wet winters and hot dry summers with about 300 – 350 mm of rain per annum.
• Cultivated
  • mainly in the Cederberg area about 250 km north of Cape Town.
  • adapted to the highlands with hot, dry summers and cold, wet winters.
  • rainfall = 300–350 mm p.a.
  • likes well-drained sandy soil.
  • no fertilising is required.
• Harvested, cultivated Aspalathus linearis is used as Rooibos tea.
  • It is rich in polyphenol antioxidants, but has a low tannin content and no caffeine.
  • Rooibos Limited in Clanwilliam (Western Cape) is the market leader in the supply of rooibos. It has a local market share of 80% and an international market share of between 50 and 60%.
  • There are over 200 contracted farms involved in the supply of rooibos.

3.5.2 Honeybush tea (Cyclopia intermedia)

• Endemic to South Africa.
• Sweeter than rooibos.
• Contains isoflavones (reduces cholestrol and high blood pressure).
• 23 species grow in the Cape fynbos biome; 5 of these are now cultivated as a commercial crop, with a production of more than 100 tons of processed tea p.a.
• Adapted to the same climate and soil requirements as rooibos.

Unit 4: Fodder Crops

• Cultivated to feed livestock; Includes hay, straw, silage, compressed and pelleted feeds, oils, mixed rations, sprouted mealies and other grains.
• There are a number of reasons why fodder is important in the keeping of livestock:
  • It provides all the nutrients that livestock require
  • It is relatively cheap to provide livestock with fodder, such as hay
  • A growing fodder is a wildlife habitat and provides watershed protection for rivers
  • Growing fodder conserves the environment by preventing water and wind erosion.
  • Can be classified as legume fodder crops and grass fodder crops.

4.1 Legume fodder crops
Trifoliate plants that bear seeds in pods (e.g. beans) and nuts in shells (e.g. peanuts).

4.1.1 Lucerne (Medicago sativa)

• Also known as Alfalfa (which means ‘best fodder’)
• The most important fodder crop grown under irrigation in the Karoo.
• Does well in most South African soils. It is drought resistant. It can be cultivated under dry conditions, where the annual summer rainfall is higher than 400 to 500 mm, and in winter rainfall, where the annual rainfall is higher than 350 to 400 mm. Lucerne grows well in deep and well-drained neutral soil, which must be free of impervious layers.
• Lucerne:
  • is very rich in protein and minerals
  • produces a very high yield per hectare
  • has a sweet taste for all ruminants
  • the roots fix nitrogen in the root nodules → released as nitrates into the soil.

4.1.2 Red clover (Trifolium pratense)

• One of the clover species that is used as a fodder crop in South Africa.
• Clovers are annual or perennial herbs. They regenerate freely and produce a lot of fodder.
• Red clover grows in a wide range of soils, but prefers well-drained loamy soils. Drought resistance is high when grown on deep soils because of the deep-rooting characteristic. Optimum temperatures for growth are between 200 and 250ºC, with mild winters.
• It is a rich source of protein in the diet of ruminants. It is also a good source of hay and can be mixed with rye grass fodder for ruminants.

4.2 Grass fodder crops
Grass fodder is the cheapest fodder for farmers who domesticate animals; grass constitutes the largest vegetation in the world.

4.2.1 Kikuyu grass
Kikuyu grass is a perennial low-growing, warm-season grass adapted to wetter regions. It is mostly fed to dairy cattle in wetter areas as grazing grass.

• Ideal as a fodder grass because it stays fresh and green for long periods, thus maintaining its water and nutrient content. It goes dormant under unfavourable conditions, like drought, but grows vigorously with the onset of favourable conditions.
• It has deep roots and spreads fast. It has underground runners (rhizome) and stolons (above ground runners) which makes it a good fodder crop for controlling soil erosion. Kikuyu can easily invade other vegetation under favourable conditions.

4.2.2 Rye grass

• There are two basic types of rye grass:
  • Annual rye grass: useful in pasture because it grows fast and therefore provides quick, short-season forage and hay forage, and prevents soil erosion. It is a cheap source of fodder for ruminants.
  • Perennial rye grass: very palatable and easily digestible in ruminants. It is fast growing, but easily invades or competes with other grasses in the field.
• Rye grass is a fast-growing cool-season grass that adapts to many soil types and climatic conditions.
• In warmer regions, rye grass requires irrigation to maintain colour and nutrients.

Unit 5: Forests

5.1 The concept: Forests
There are natural forests and plantations in South Africa.

• Natural forest = a multilayered vegetation unit dominated by trees (evergreen or semi-deciduous), with 75% or more crown cover and very little grass.
  • Found mainly in the mountain areas near the coastal belts of the Eastern Cape.
  • They cover 504 803 ha of South Africa.
• Plantations = area planted with trees for commercial use.
  • In South Africa = 1,3 million ha (one of world’s biggest).
  • A commercial plantation = blocks of trees where the trees of one block are all mostly the same species and age, and have all been planted at a fixed spacing.
  • These species are mostly exotic and are light-demanding.
  • Harvesting is by felling a whole compartment at the same time.
  • Commercial plantation forestry in South Africa = the large planted forests →
    supply raw materials (e.g. mining; construction; furniture; paper; energy).
• The forestry sector employs about 170 000 people and contributes more than R16 billion annually to the economy of South Africa.

5.2 Classification of forests
Forest crops (wood) can be classified into:

• Hardwood: from deciduous trees, e.g. oak, maple and mahogany,
• used in construction for trusses, beams, and doorframes
• Softwood: from evergreen or coniferous trees, e.g. pine and cedar.
• used for making indoor furniture, such as kitchen cupboards.

5.3 Indigenous forests (natural forests)

• Occur mainly along the southern and eastern highlands of South Africa.
• Good source of herbal medicine, building materials, fuel wood (e.g. for fires).
• A habitat for most wild animals like monkeys.
• Indigenous trees = hardy and well adapted to the climate of South Africa. Indigenous trees live long and some (e.g. Baobab) can grow very big.

5.4 Exotic trees

• From other countries, reaching new areas outside of their origin in one of two ways:
  • self-introduction on their own → has been happening over millions of years at a slow rate through wind and water
  • with human assistance that may be deliberate or accidental → for food or aesthetic purposes, or as part of international commerce.
• An example of an exotic tree in South Africa = eucalyptus (gum) tree. Some exotic trees → economic and aesthetic value; others → invasive and detrimental to the ecosystem, e.g. the gum tree extracts volumes of soil water from aquifers.

5.5 Promotion of protected trees and eradication of invasive trees

• Invasive alien species are one of the main threats to biodiversity.
• They impose enormous costs on agriculture, forestry, fisheries and other human enterprises, as well as on human health.
• Rapidly accelerating human trade, tourism, transport and travel over the past century have enhanced the spread of invasive species.
• Invasive trees:
  • grow faster, and so they mature earlier
  • produce many more seeds for self-propagation
  • are not known by the local animals so their leaves are not disturbed by rodents
  • herbalists do not disturb them because they are foreign
  • lead to loss of agricultural land
  • threaten the quality and quantity of soil water
  • invade grazing-land for animals
  • multiply rapidly to take over the indigenous trees in an area.
• Environmental researchers estimate that over 10 million hectares of land in South Africa is occupied by alien plants. If not controlled effectively, they will:
  • affect our water resources
  • take over most of our arable land
  • increase bush fires
  • cause soil erosion
  • pollute water and affect aquatic life.
• it will cost the government over R600 million a year over 20 years to control the spread of alien plants.
• According to the ARC, there are four basic methods to control invasive alien plants:
  • Mechanical control: removing the invasive plants by physically uprooting them, slashing, mowing, ringbarking or bark stripping them.
  • Chemical control: the application of registered herbicides to the invasive plants or to the soil surrounding them with the aim of killing them.
  • Biological control: the use of host-specific natural enemies to reduce the population of the invasive plant to the barest minimum.
  • Indirect control: the use of other methods that do not directly control the plants, but involve measures such as:
    • the use of fire
    • checking entry ports for introduction of alien crops
    • over-sowing beneficial plants at areas infested by alien crops.

Topic 6: Questions

• Answer the questions below.
• Give yourself one hour.
• Check your answers afterwards and do corrections.

Questions

1. How much of South Africa’s land can be used for crop production? (1)
2. Name the five largest contributors towards the gross value of field crops for the past five seasons, and state the contribution of each as a percentage. (10)
3. Give five reasons, apart from their importance to the economy, why plants are important. (5)
4. Indicate whether the following statements are true or false: (15)
   1. In terms of value of production, wheat is the second most important field crop produced in South Africa.
   2. Soya beans contribute about 4,9% to the gross value of field crops.
   3. The South African sugar industry produces an average of approximately 2,2 million tons of sugar per season.
   4. South Africa has one of the largest commercial plantation areas in the world, covering 1,3 million ha.
   5. Stem vegetables require deep soil with a pH range of 5,5 – 7,6.
   6. Leaf vegetables require an average daily temperature of 15 – 20oºC.
   7. Carrots require low temperatures to flower.
   8. Cauliflower is not resistant to frost.
   9. Deciduous fruits require cold, wet conditions during some months of the year.
   10. Apples are a subtropical fruit.
   11. Fynbos requires extremely poor soil and intense fires every 4 – 20 years.
   12. The roots of lucerne fix nitrogen in the root nodules.
   13. Rooibos requires and annual average rainfall of 450–600 mm.
   14. Red clover grows in a wide range of soils, but prefers well-drained loamy soils.
   15. Fodder provides all the nutrients that livestock require.
5. What does the study of agronomy include? (4)
6. List the five categories of vegetable classification and give an example of each. (10)
7. Describe the climatic and soil requirements of bananas. (3)
8. What are the three main types of flower crops grown in South Africa? (3)
9. Name four negative effects alien plants have on the environment. (5)
10. Describe the five ways in which alien plants can be controlled. (10)
11. Name the two categories of fodder and give an example of each. (4)

[Total mark: 70]