Units

• OVERVIEW 
• Unit 1 Ecology and agro-ecology
• Unit 2 Interactions in ecosystems
• Unit 3 Grazing ecology
• Unit 4 Pasture or veld management
• Unit 5 Biomes of South Africa
• Unit 6 Climate change and effects of weather phenomena
• Topic questions

Agro-ecology

Overview

Unit 1: Ecology and agro-ecology

1.1 Basic concepts
1.1.1 Ecology
Ecology is the branch of biology that deals with the relations of organisms to:

• one another
• their physical surroundings.

1.1.2 Agro-ecology
Agro-ecology is a special branch of ecology. It looks at how these relations of organisms to one another and to their physical surroundings apply to agriculture.

1.1.3 Agro-ecosystems

• A farm is an ecosystem. It includes agricultural plants and systems, and so it is called an agro-ecosystem.
• Knowledge of agro-ecology and agro-ecosystems helps us to:
• choose the best animals and plants to farm on a particular piece of land
• use the land in a productive way to provide food, fuel and fibres
• preserve the land for the use of future generations.

1.2 Levels of ecological organisation
1.2.1 Biosphere
The biosphere is that part of our planet Earth (crust, water and air) that supports living organisms. There are three main environments on Earth:

• the sea
• fresh water
• land.

1.2.2 Biomes
Different parts of the land have different climates. Climates divide the land into smaller environments called biomes or ecological regions. Biomes are areas that have similar types of plants and animals. The plants and animals in one biome are different from those in other biomes. There are six main biomes or ecological regions on Earth:

• forests
• Savanna
• Grasslands
• Tundra
• semi-deserts
• deserts.

An environment (ecosystem) consists of living things and non-living things. The living things are structured into layers, or levels of organisation:

• community: all the plants and animals in the ecosystem (e.g. a forest consists of trees, moss, ferns, birds, insects, etc.)
• population: a group of organisms of the same species (e.g. all pine trees in a forest)
• individual: the separate members of a population (e.g. a single pine tree).

1.3 Components of ecosystems

An ecosystem consists of non-living things (abiotic factors) and living things (biotic factors).

1.3.1 Abiotic factors
Physiographic factors
Physiographic factors refer to the appearance of the land (rivers, hills, mountains or valleys). The appearance of the land is determined by the slope, aspect and altitude. These affect plant growth because they affect the climate.

• Slope: a measure of the steepness of the land.
  • In heavy rain, water that doesn’t enter the soil runs down the slope. The steeper the slope, the more runoff; therefore, steeper slopes support less plant growth. There are three types of slope: flat land, gentle slope and steep slope.
• Aspect: the direction in which the slope faces (N, S, E, W).
  • The climate of a slope changes with the aspect. In the southern hemisphere, north-facing slopes are usually hotter and drier than south-facing slopes. West- facing slopes have afternoon sun, whereas east-facing slopes have morning sun. West-facing slopes are usually hotter and drier than east-facing slopes, but not as hot as north-facing slopes.
• Altitude: the height above sea level.
  • Temperature decreases with increasing altitude because the atmosphere (which holds heat) gets thinner higher up. Altitude can cause the climate to change over very short distances.

Climatic factors
Climate is influenced by:

• Sunlight: intensity and duration per day. Plants need sunlight to photosynthesise.
• Temperature: how hot or cold the air is. Temperature decreases as we move from the equator towards the poles – affects plants and animal life.
• Rainfall: plant and animal life are influenced by:
  • precipitation: water that comes from the air – rain, hail, frost, snow, dew and mist
  • average annual rainfall: the amount of rain that usually falls in one year, measured in millimetres. (Ecosystems with a high average annual rainfall support more plant and animal life than those with a low average annual rainfall. Water-loving plants grow in wet areas; drought-tolerant prefer low rainfall.)
• Wind: plants use the oxygen in air for photosynthesis.
  • the direction and strength of the wind influences an ecosystem
  • wind influences rainfall patterns, for example, wind from the sea contains more moisture than wind from the land
  • wind spreads seeds and pollen.

Edaphic factors (factors that influence the soil)

• Soil types differ in:
  • size of the soil particles
  • amount of water they hold
  • amount of air they contain
  • colour
  • depth
  • type and amount of minerals they contain.
• Soil texture:
  • sandy (grainy and loose)
  • clay (sticky and dense)
• Soil depth:
  • from a few centimetres to over two metres deep
  • plants get minerals, water and air from soil, so deep soils support more plant growth than shallow soils.
• Soil water:
  • refers to water holding capacity (the ability of soil to hold water), for example:
  • sandy soils drain quickly and have poor water holding capacity – can’t support much plant growth
  • clay soils hold a lot of water and drain slowly – contain little air, e.g. wetland areas.
• Soil fertility:
  • fertile soil contains many nutrients and supports plant growth
  • poor soil lacks nutrients and doesn’t support plant growth.

1.3.2 Biotic factors

• Producers: Green plants that make their own food through photosynthesis.
• Consumers: Organisms that can’t make their own food; they eat other organisms:
  • herbivores (cows and sheep) feed on plants
  • carnivores (lions) eat animals
  • omnivores (people) eat plants and animals.
• Decomposers: Break down dead plants and animals through decay – minerals return to the soil.

Unit 2: Interactions in Ecosystems

2.1 Energy flow in ecosystems
Energy flows from one thing in an ecosystem to another:

• the sun (non-living) is the main source of energy in an ecosystem
• plants (living) change sun energy into chemical energy, in the form of carbohydrates
• animals eat the plants and absorb the energy
• the energy is passed on from one living thing to the next.

2.1.1 Food chains
A food chain is a hierarchical series of organisms. Each organism in the chain is dependent on the next organism as a source of food.

A food chain
Sunlight is a source of light energy. The sunflower uses nutrients from the soil + water + carbon dioxide, to change the sun’s light energy to chemical energy, or food. The mouse eats sunflower seeds. The snake eats the mouse. The owl eats the snake. When the owl dies, it will decompose, and the nutrients return to the soil.
Each step in this food chain is called a trophic level:

• the producers (plants) are the first trophic level
• the herbivores that eat the plants are the second trophic level
• the carnivores are the third trophic level.

2.1.2 Food webs
Animals do not only eat one type of prey. For example, snakes eat mice, insects, small birds and frogs. A food web is a way of showing all the connected food chains in an ecosystem.

A food web

2.1.3 Ecological pyramid
An ecological pyramid is a diagram to show all the trophic levels in an ecosystem.
The first trophic level is the bottom of the pyramid.

• The first trophic level consists of producers.
• This level contains the most energy.
• Energy decreases as it goes up through the levels.
• Some food chains only have three trophic levels, whereas others have five. 

An ecological pyramid

2.2 Nutrient cycling in ecosystems
The supply of nutrients in an ecosystem (water, carbon, nitrogen) is limited. They move through ecosystems in continuous cycles:
non-living things → living things → non-living things.

2.2.1 The water cycle

The water cycle
Water molecules move continuously from one reservoir to another:

• Water in the ocean or a river = in the liquid phase.
• Evaporation: water changes to the gas phase / water vapour.
• Sublimation: ice changes to vapour.
• Evaporation and sublimation use heat energy from the sun.
• Condensation: vapour rises up into the atmosphere and cools down – form drops (change back into liquid).
• Precipitation: drops combine with others – form clouds – become heavy and fall to the ground as rain, snow or hail.

The sun heats the Earth: surface water + water in the soil evaporates and rises into the air. Plants take up soil water with their roots. This water moves up through the plant and evaporates from the leaves. The water in the air rises and forms clouds. The clouds produce rain and the cycle begins again.

2.2.2 The carbon cycle

• Carbon = a building block of vitamins, carbohydrates, fats and proteins.
• Main source of carbon = carbon dioxide (CO₂).
• Photosynthesis: plants use CO₂ to make organic substances, for example, carbohydrates.
  • Carbohydrates contain carbon.
• Living organism eats the plants and absorbs the carbon → organism dies and carbon returns to the soil.
• Living organism breathes in oxygen and breathes out CO₂ → carbon returns to the atmosphere in the form of CO₂.

2.2.3 The nitrogen cycle

• Nitrogen = building block of protein.
• Nitrogen forms part of the atmosphere, but living things can’t absorb it from the atmosphere:
  • Step 1: Nitrogen fixing. Legumes have bacteria on their roots. Bacteria fix atmospheric nitrogen by changing it to ammonia (NH₃).
  • Step 2: Nitrification: Nitrifying bacteria in the soil changes the ammonia to nitrates (NO₂). Plants can absorb nitrates.
• Lightning and fertiliser add nitrogen to the soil.
• When plants die, they are broken down by decomposers and the nitrogen is returned to the soil in the form of ammonia. Nitrifying bacteria in the soil change the ammonia to nitrates (NO₂).
• Heavy rain: denitrifying bacteria change nitrates back to nitrogen gas, which returns to the atmosphere.
• Leaching: nitrates are soluble. When water runs off, nitrates are removed from the soil. Nitrates in drinking water are harmful to humans and animals.

2.3 Interaction between organisms in ecosystems
2.3.1 Competition
Organisms compete for limited resources (food, water, territory):

• Intraspecific competition: animals of the same species (e.g. two male lions) competing to mate with the same lioness.
• Interspecific competition: animals of different species (e.g. cheetahs and lions) competing for same prey.

Competition affects the structure of the community. Animals or species that cannot compete effectively will leave the ecosystem or die.

2.3.2 Predator and prey
Predation is when a predator (the animal that hunts) eats its prey (the animal that is hunted). There are different forms of predation:

• a lion ambushes and kills its prey, and eats it
• a snake swallows its prey (frog) whole
• a jellyfish subdues prey with venom before eating it
• a rattlesnake’s venom starts to digest the prey even before swallowing it.

2.3.3 Mutualism
Both organisms benefit from the relationship, for example, ungulates and bacteria in its intestines:

• bacteria produce cellulase (enzyme) that digests cellulose = benefits ungulate because their food is digested
• bacteria benefit because they live in an environment that supplies food.

2.3.4 Commensalism
One organism benefits, the other doesn’t, but is not harmed either, for example, a shark and remora:

• remora attaches itself to shark – benefits = transport and food.
• shark does not benefit, but is not harmed.

2.3.5 Parasitism

• One organism (parasite) lives on or within and feeds on another (the host).
• The parasite benefits, but the host is weakened, for example, dodder (visible) on plants and cholera bacterium inside the digestive tract of humans.
• In both cases the host is harmed while the parasite benefits.

2.4 Ecological farming methods
In the past, conventional farming methods were used to increase yields and maximise profits without concern for the environment, for example:

• synthetic fertiliser to increase the yields of crops
• herbicides to get rid of weeds
• pesticides to get rid of pests
• hormones and antibiotics.

From the end of the 1900s: ecological farming systems started becoming popular. 

2.4.1 Organic farming
Does not use:

• synthetic fertilisers, herbicides and pesticides on crops
• hormones, food additives, antibiotics for livestock
• hormones or food additives to promote growth in livestock
• antibiotics to rid livestock of diseases, unless necessary.

Does use:

• crop rotation – growing a different crop on the same land each year for 3 – 5 years to rest the soil because different crops:
  • absorb different nutrients from the soil
  • attract different weeds and pests (crop rotation prevents weeds and pests from establishing themselves).
• green manure – a cover crop that is planted to add nutrients and organic matter to the soil.
  • This crop is left on the land for a while, and then ploughed into the soil.
  • Clover is often used for bacteria (nitrogen fixing)
• compost – decomposed plant matter to add nutrients
• biological pest control – natural enemies
• mechanical weed control – with implements, e.g. a cultivator or hoe.

2.4.2 Biological farming
Farmers use biological farming systems, for example:

• ensuring soil has correct nutrient balance:
  • the soil is tested for ten nutrients (boron, calcium, copper, iron, magnesium, manganese, phosphorus, potassium, sulphur and zinc) to determine the amount of nitrogen to be added
• ensuring that soil contains sufficient microbes for correct pH level (acidity and alkalinity)
• using natural fertilisers, such as compost, as far as possible
• no herbicides and pesticides
• rotating crops every year or two.

2.4.3 Conservation farming
Farmers use natural ecological processes to:

• get rid of pests and weeds
• reduce soil erosion on their farms
• increase the soil’s fertility and structure
• save water.

They do this in three ways:

• minimal soil disturbance: no land tilling – soil is not disturbed so
  • soil minerals are maintained
  • erosion is minimised
  • water is not lost from the soil
  • production cost due to tilling is saved.
• retaining crop residues – the land isn’t tilled, so residues of previous crops create a permanent organic cover (mulch):
  • prevents soil erosion
  • prevents soil moisture from evaporating.
• crop rotation with two or more crop types – frequent crop rotation = natural pesticide and herbicide because different crops attract different weeds and pests.

2.4.4 Game farming
The hunting and the selling of live game animals and game products (e.g. venison, hides, etc.)

2.4.5 Sustainable or alternative farming
Uses the same approach as biological and organic farming:

• crop rotation
• avoid or minimise the use of pesticides, herbicides and fertilisers
• cover the soil to minimise erosion and control weeds
• control pests with natural predators
• enrich the soil by organic methods.

Unit 3: Grazing Ecology

3.1 Natural and artificial pastures

• Natural pasture:
  • an area where people have not intervened.
• Artificial pasture:
  • an area where people have planted grass types or other plants for grazing: first remove the existing vegetation and then sow seeds of a grazing plant, e.g. alfalfa or orchard grass.

3.2 Grazing ecology

• A pasture is an ecosystem on its own, because it has a selection of living and non- living things within the same environment.
• The study of the relationship between the parts of the pasture’s ecosystem is called grazing ecology.
• Grazing ecology determines the type and number of animals that can be kept on a piece of land.

3.2.1 Ecological succession in grassland
The type of veld growing in an area can change as time passes. If this happens by itself, without the interference of people, it is called plant succession or ecological succession.
On a ploughed area of bare soil, plants will start to grow on the bare soil. The first plants to grow will not be the same as the plants that were there before the land was ploughed:

• The first plants to grow on bare land (pioneer species) are usually annuals.
• After some time, perennial plants, including grasses, begin to grow on the land.
• The type of perennial grasses changes over time.
  • If the temperature and rainfall are high enough, woody bushes and then trees start to grow amongst the grasses.
  • If there is no fire to destroy the woody plants, then the area will become covered in forest. The change from pioneer species to forest can take a long time.
  • The plants in the forest are called climax species. Forest plants are called climax species because there will not be much more change in the type of plants once the forest stage is reached.
  • If the temperature and rainfall are not high enough for forest to grow, or if regular fires kill the woody plants, the climax species will not be forest plants, but some other type of veld, for example:
    • In the grasslands of the cool lower rainfall areas, perennial grasses are the climax species because the climate stops them from changing from grass into another veld type. The climatic climax grasslands are usually sweetveld.
    • If there is no fire, the grasslands in the warm high rainfall areas in the east of the country will slowly change into forest. The climate in this area is suitable for forest, but fires keep the area a grassland.
    • In the Karoo, small bushes are the climax species because low rainfall stops the Karoo veld from changing to forest.
    • In the savanna areas, low trees and grass are the climax species. The temperatures are high enough for trees to grow, but the low rainfall stops the change to forest.

Grasslands at the climax stage are the best for grazing animals. Climax species of grass are usually the most palatable (soft, tasty and nutritious).
Pioneer species are usually unpalatable (tough, taste and smell bad). Grazing and invader plants can also cause ecological succession.

Grazing

• Overgrazing
  • There are more grazing animals than plants for them to eat.
  • The animals eat most of the grass plants → the plants do not set seed → few new plants grow → perennial grass plants get weak because they do not have time to re-grow → soil is left bare → it begins to erode → pioneer species (unpalatable) become plentiful.
  • In savanna veld, bushes grow more thickly → the veld can no longer be used for grazing animals, such as sheep and cows.
• Selective grazing
  • Animals eat the most palatable plants and leave the unpalatable ones → only the unpalatable plants remain and the veld is of little use for grazing farm animals.
• Undergrazing
  • This happens in fire climax grasslands, when the climax species begin to be replaced by taller species as the grassland slowly begins to change to forest.
  • These taller grass species are good for thatching roofs, but are usually unpalatable.

Plant invaders
Invaders are brought by people from another area or country, e.g. Lantana, Imbricate cactus, Port Jackson.
Because they have no natural enemies, they increase fast and replace the plants that used to grow in the veld.

3.2.2 Adaptations by game animals before agriculture
Before organised and commercial agriculture, there were no fences, farm boundaries or grazing camps.

• Large herds of game moved across southern Africa in search of grazing and water.

Results

• Short periods of high intensity grazing, followed by a long period of rest during which the veld could recover fully.
• Veld was not over-grazed because it was grazed by different species of animals – not only by one kind of livestock: some species grazed close to the ground, others further from the ground, while some species grazed small trees; also, some species preferred one type of grass, while others preferred another type.
• Different animals have different trampling patterns, so the veld did not become completely trampled in one spot.
• Natural veld fires occurred when the veld conditions could benefit, and not during every season.

These are the natural, balanced grazing conditions that modern ecological pasture scientists are trying to copy.

3.2.3 Selective and non-selective grazing
Selective grazing happens when grazing animals do not graze all the plants in a particular area, but prefer certain plants, for example:

• type of animal – some animals are ‘picky eaters’ (sheep are more selective in what plants they eat).
• plant selection – animals eat only the palatable plants, and leave the unpalatable ones. After a time, only the unpalatable plants remain and the veld is of little use for grazing farm animals.
• height selection – animals only eat a part of the plant, preferring to leave the lower parts of the plant.
• area – this is when animals prefer a certain area in the veld, such as next to a river, or if animals are kept in camps, they might prefer a certain spot in the camp.

Non-selective grazing happens when you force the grazing animals also to graze the unpalatable grasses. This happens when the veld is dominated by unpalatable grass. However, overgrazing can happen easily.

3.2.4 Zero grazing
Animals are enclosed and fodder brought to them to prevent tick-borne diseases and other health hazards. This is often done in dairy farming.

3.3 Optimal grazing
Optimal grazing refers to making the best use of the available veld or pasture. For optimal grazing you must consider:

• carrying or grazing capacity
• stocking rate (SR).

3.3.1 Carrying or grazing capacity
The grazing capacity is the average number of animals that a particular farm can sustain over a period of time. The grazing capacity is based on the stocking rate.

3.3.2 Stocking rate (SR)

• SR = the number of animals that can graze on one hectare of land, for the grazeable part of one year (not winter), without doing damage to the condition of the veld.
• If more animals than is indicated by the SR are allowed to graze = overgrazing and the veld is damaged: most of the grass is eaten → no seed is produced → no new plants grow → bushes grow more thickly and veld becomes unsuitable for grazing.

3.4 Veld types of southern Africa
In southern Africa there are three veld types:

Climate, soil and plant characteristics of veld types

3.5 Characteristics of grazing plants
3.5.1 Nutritive value
Grazing plants differ in their nutritive value. Some plants are more nutritious than others. Some plants are only nutritious for parts of the year (season of use).
Nutritive value of sourveld and sweetveld

• Sourveld can be grazed only during the growing season (spring and summer):
  • the excess must be cut and baled
  • in autumn, the grasses become unpalatable (plants move the nutrients to the roots)
  • sourveld is found in the high rainfall areas (east), so it grows thickly.
• Sweetveld can be grazed the whole year:
  • it is found in drier areas than sourveld, so it grows less thickly than sourveld
  • fewer animals can graze on an area of sweetveld than on the same area of sourveld, but they can graze throughout the year
  • sweetveld also retains its nutritional value throughout the growth season.
• Mixed-veld is a mixture of sweetveld and sourveld
  • it can be grazed for 6–11 months of the year.

In the past, communities in sourveld and mixed-veld areas moved their cattle to nearby sweetveld areas when the grasses became unpalatable. This is no longer possible for many communities, so farmers in sourveld and mixed-veld areas have to find other ways to feed their animals when grasses are unpalatable.

3.5.2 Resistance to grazing and ecological status

• Grazing resistance is the ability of plants to survive and grow in grazed systems.
• Light to moderate grazing can:
  • stimulate plants to grow
  • increase their nutritive value
  • increase the cycling of nutrients.
• If a pasture is over-grazed, the plants don’t produce enough seeds and the roots show decreased growth, so the grazed plants can’t compete with others.
  • Therefore, the composition of the plant community changes → the grazed plants are replaced by weedy species that are more resistant to grazing and less productive and palatable than those with low grazing resistance.
  • Ecological succession takes place:
    • palatable plants are replaced with less palatable plants
    • the ecological status of the grazing area changes back to the pioneer stage.

3.6 Scientific method to determine the condition of pastures
The condition of the veld must be monitored to change the grazing procedures before it is damaged. It is difficult to return damaged veld to a productive state.

3.6.1 Condition of pastures
The condition of the veld depends on two factors:

• the type of plants growing there → veld is in –
• good condition if most of the plants are palatable
• poor condition if most of the plants are unpalatable.
• the amount of soil that is covered by plants, as bare soil erodes easily → veld is in –
• good condition if most of the soil is covered by plants
• poor condition if a lot of the soil is bare.

3.6.2 Pasture condition scoring
The farmer walks through the pasture and scores 10 categories on a scale from 0 – 4 to:

• determine condition
• see what can be done to improve condition.

The following categories are examined:

1. Plant desirability
   • Desirable plants: provide nutrition of a high quality for the biggest part of the season, (e.g. cool season grasses, legumes and warm season grasses).
   • Undesirable plants: plants that animals don’t graze (e.g. thistles, toxic or woody plants).
   • Intermediate plants: palatable but not nutritious (e.g. dandelions). Species mostly undesirable = 0. Species mostly desirable = 4
2. Plant diversity
   • The number of different kinds of plants in the pasture:
     • Only one type of plant = narrow diversity
     • More than five kinds of plants = broad diversity; important to keep the pasture in good condition.
       Narrow diversity = 0. Broad diversity = 4
3. Plant density
   • How close together the plants in the pasture grow: bare spots encourage erosion and the growth of weeds.
     % of ground cover less than 55% = 0. % of ground cover more than 95% = 4.
4. Plant vigour
   • Do the desirable and intermediate plants (see category 1) grow healthily?
   • Do they have a healthy colour and re-grow quickly after grazing? Desirable plants grow weakly = 0. Desirable plants grow strongly = 4.
5. Legumes in pasture
   • Important for binding atmospheric nitrogen into the soil → improves soil quality.
   • grow strongly during hot, dry periods, when other desirable plants don’t grow strongly
     % of legumes less than 10% = 0. % of legumes more than 40% = 4.
6. Severity of use
   • How many animals?
   • How often?
   • Beware of under-grazing and overgrazing.
     Light use, not very often = 0. Heavy use, very often = 0. Moderate use with adequate resting periods = 4.
7. Uniformity of use
   • Are the plants grazed evenly, to a similar height, OR
   • Spotty grazing, where some parts of the pasture are grazed, and other parts are not grazed?
     Spotty grazing = 0. Even grazing = 4.
8. Soil erosion
   • If the plant cover on sloping areas is not dense enough → soil erosion. Heavy erosion = 0. Slight erosion = 4.
9. Woody canopy
   • Trees provide shade for animals, but:
     • can also block sunlight
     • compete with grass for water and nutrients
     • can cause uneven grazing and manure distribution in the pasture
     • if animals group together below a tree, they trample the ground → erosion.
       % of pasture covered by tree canopy more than 40% = 0. % of pasture covered by tree canopy less than 11% = 4.
10. Plant residue
    Decaying plant material gives nutrients to the soil, but:
    • too many decaying plants, the nutrients will not be properly cycled (a layer of more than 4 cm deep).
    • too little decaying plants, water will run off more easily from the ground (a layer of less than 1 cm deep).
      Too little decaying material = 0. Too much decaying material = 4.

Add up the scores and evaluate the condition of the pasture:

Signs that the condition of the veld is getting worse

• The ground cover by grasses is decreasing. There are more and bigger areas of bare soil.
• There are fewer perennial grasses. Many of the grass plants grow from seeds after rain falls.
• The bushes are growing more thickly, especially those that animals do not like to eat.
• More animals are dying from eating poisonous plants.
• Animals produce less milk and young than they used to.
• People show signs of malnutrition because of the shortage of animal products to eat.

Unit 4: Pasture or Veld Management

4.1 Importance of pastures for the livestock industry in South Africa
Pastures are the foundation of the livestock industry in South Africa. It provides food and plays other important roles:

• It is the primary source of food for livestock in commercial and subsistence farming.
• The higher the quality of food that livestock get, the better the quality of products that we get from them.
• It provides a source of genetic material for pasture plants.
• If the biodiversity of pastures decrease, the general quality of pastures decreases.
• It maintains agricultural resources.
• Well-managed pastures prevent soil erosion, because plant cover is kept intact.
• Water sources are maintained, because soil does not wash into rivers, and water runoff is kept to a minimum.
• Well-managed pastures keep the natural balance in the environment, by cycling nutrients (nitrogen fixing) and maintaining the balance between oxygen and carbon dioxide in the atmosphere.

4.2 Relationship between pasture management and pasture condition
A pasture is an important natural resource, so management is important.

• Pasture management = manipulating the natural vegetation to increase productivity.
• Proper pasture management improves and maintains the health and function of a pasture. Only a pasture that is in good condition can be productive.
•  A pasture that is in good condition:
• has enough nutritious grazing plants.
• So, the purpose of pasture management is to remove undesirable plants (such as weeds) and to make sure that the pasture has the maximum amount of climax species.
• has no bare patches.
• Pasture managements prevents over-grazing and keeps the pasture properly drained.
• If water remains after the rain, grazing plants will ‘drown’. If that area is then grazed, bare patches will form.

4.3 Veld management practices
4.3.1 Stocking rate (SR)
SR is the number of animals that can graze on one hectare of land, for the grazeable part (not winter) of one year, without doing damage to the condition of the veld.

4.3.2 Animal ratio

• The term ‘animal ratio’ is used when more than one type of animal grazes the same pasture, for example, sheep, goats and cattle.
  • The animal ratio is the ratio between the different animals grazing the same pasture.
• It is important to know which type of food each animal type prefers, to make sure that all animals get enough food to eat, while still managing the pasture properly to prevent over-grazing.
• The type of diet each type of animal prefers, is influenced by factors including:
  • their behavioural patterns (e.g. goats graze on the higher ground, while sheep do not)
  • their anatomy (the characteristics of the body of the animal)
  • physiological requirements and limitations (e.g. some types of animals need more cellulose than other types)
  • body size (larger animals need more food than smaller animals).
  • Animal ratio can also refer to the ratio between male and female animals, for example, a dairy farmer keeps more cows than bulls.

4.3.3 Grazing systems
A grazing system is a particular strategy that a farmer uses to let his animals graze. It is important for the farmer to know the conditions on the farm:

• the type of plants on the farm
• the type of livestock he keeps and their feeding preferences.

There are three types of grazing systems:

• slow rotational grazing
• continuous grazing
• game and communal grazing.

Slow rotational grazing

• The grazing area is divided into camps:
• one is grazed while the others are rested.
• The camps are usually fenced, but the animals can also be herded.

The diagrams on the next page show slow rotational grazing with two camps and with four camps. These types of camps allow the veld to rest so that the grass plants can produce seeds and store food in their roots.

A six-camp rotation over two years (above); a four-camp rotation (below)

Four factors must be kept in mind when considering a slow rotational grazing system:

1. The number of animal units that will be using the grazing system.
   • Calculate the forage requirements of the herd.
   • This is done in animal units (AU): 1 AU = the daily forage needed by a dry cow (approximately 12 kilograms of dry forage per day).
2. The size of the area that will be needed to graze that number of animals: this depends on:
   • the feeding requirements of the herd
   • how much forage the veld produces.
3. How large each camp should be, which depends on:
   • the amount of available pasture at the beginning of the grazing period
   • the AU of the herd
   • how long each grazing period should be.
4. The number of camps needed, which depends on:
   • the number of days that the animals will graze in the veld
   • how long the rest period should be.
   • The length of the rest period depends on how quickly the pasture re-grows, which is influenced by the weather conditions and the season.

Continuous grazing
This is when animals graze the same area at all times of the year:

• usually used in communal grazing lands
• the animals move freely in search of food except when they are herded during the crop-growing season.

Game and communal farming
Communal farming = when animals roam freely without any fences and grazing camps.

• was practised in traditional farming before the arrival of Europeans when there was enough land for communities to move their animals to fresh grazing areas so that grass had time to grow and set seed before it was grazed again
• provided a better opportunity for animals to live in a more natural habitat.

Fencing and owning of land by single farmers stopped many communities from moving their animals to fresh grazing lands. The result is:

• not enough grazing land for all the animals of the community
• communal grazing lands become overused
• each person owned fewer animals
• a decrease in the amount of meat and milk produced.

Today there are very few communities that farm communally. Game farmers practise communal farming because game needs more space to move around.

4.3.4 Veld burning
Burning can damage the veld and must only be done according to the following rules.

Sourveld
Sourveld becomes unpalatable in winter. If sourveld grass has not been grazed low for a long time, dead leaves collect above the roots. Fire is used to remove dead leaves. This helps the animals to reach the new green growth and lets the new growth get enough sunlight to grow well.

• Burn only after the first rains in spring when there is enough water for new growth to protect the soil. (Some farmers burn in winter, before the rains, to give their animals grazing when it is scarce. This damages the veld because the grasses do not have enough water. When the first rains fall, there is less grass covering the soil and it can erode easily.)
• Do not burn an area more often than once every four years.
• Burn on a cool day when there is no wind, otherwise the fire can get out of control.

Sweetveld
Never burn sweetveld.

4.4 Veld management systems
Farmers need to know:

• what type of grazing their animals prefer
• what type of grazing their veld contains
• how the grazing is influenced by the grazing patterns of their animals and the weather.

Sound veld management systems involve setting up camps (farming units) that take into account the following:

• resting period
• defoliation (removal of leaves)
• weather conditions
• veld separation.

4.4.1 Resting period
Grazing plants need to rest in order for new plants to grow: use slow rotational grazing. The length of the resting period is influenced by:

• the condition of the pasture (the more damaged the pasture, the longer the resting period)
• the number of animals that graze the pasture (the more animals, the longer the resting period).

4.4.2 Defoliation (removal of leaves)
Grazing animals remove the leaves of the plants when they graze. As a result, photosynthesis takes place at a much slower rate → the plants cannot produce food for growth.

4.4.3 Weather conditions
Weather conditions influence grazing conditions:

• Heavy rainfall: pastures can easily become waterlogged → grazing plants drown → reduces the ground cover and leads to erosion.
• Drought: plants do not recover quickly from grazing → erosion takes place.

4.4.4 Veld separation
Fences between grazing camps:

• prevent animals getting into a camp that is being rested
• separate different veld types from one another, to prevent over- or under-grazing. (Animals will rather graze sweetveld than sourveld, so if a strong fence does not separate these different veld types, the sweetveld will be overgrazed, while the sourveld will be undergrazed.)

4.5 Advantages and disadvantages of grazing systems
When choosing a grazing system, their advantages and disadvantages must be considered.

4.6 Veld management practices which lead to poor pasture conditions
Good veld management practices improve the condition of a pasture. Poor veld management, like those listed below, practices can quickly damage a pasture.

• Overgrazing:
  • erosion
  • increase in pioneer species (less palatable).
• Wrong stocking rate:
  •  overgrazing
  • undergrazing.
• Not removing poisonous plants (e.g. Lantana):
  • sick animals.
  • Not allowing sufficient rest time
  • increase of pioneer species.
  • poor water management
  • if not well-drained, pasture becomes waterlogged, which leads to loss of grazing
    • groundcover must be kept intact so that if rain falls runoff is kept to a minimum.

Unit 5: Biomes of South Africa

5.1 Biomes of South Africa
There are six main types of biomes in South Africa.

Biomes of South Africa

5.1.1 Savanna

• Covers over one-third the area of South Africa.
• Characterised by a grassy ground layer and an upper layer of woody plants. If the upper layer is near the ground, it is called shrubveld. If the upper layer is dense, it is called woodland.
  • The intermediate stages are called bushveld.
• Location: Limpopo (bushveld), parts of KwaZulu-Natal, the North West province, Northern and Eastern Cape.
• Climate: warm areas with summer rainfall (650–1000 mm annually) and dry winters.
• Fauna: the wild animals of Africa (e.g. elephant, buck, rhino, zebra and giraffe) were previously found in large numbers in the savanna. Today there are many game reserves in savanna areas. Some farmers and communities keep game instead of cattle, but the area is also suitable for cattle, sheep and goats.
• Flora: combination of low trees and grass.

5.1.2 Forest

• Important tourist attraction in South Africa, but they have been exploited for timber.
• Location: in patches, with larger areas along the Garden Route (Knysna), KwaZulu- Natal, the Eastern Cape, Mpumalanga and parts of Limpopo.
• Climate: restricted to frost-free areas with high rainfall (800–1 000 mm throughout the year). Summers are warm; winters are mild.
• Flora: mostly large trees with plants that grow beneath and on the trees. Used for commercial plantations and the wood is used for paper and in the building industry.
• Fauna: Forest areas are not useful for grazing animals, as there is little grass.

5.1.3 Grassland

• The cornerstone of the maize crop, and many grassland types have been converted to this crop. Sorghum, wheat and sunflowers are also farmed on a smaller scale.
• Location: found chiefly on the high central plateau of South Africa, and the inland areas of KwaZulu-Natal and the Eastern Cape
• Climate: true grassland is found in cool areas, with 400–700 mm of rain per year, during the summertime. The summers are hot and the winters are dry.
• Flora: mainly grasses, few trees or bushes. Fire, caused by people and lightning, prevents growth of trees and bushes.
• Fauna: the grasslands are the best areas for farming grazing animals, such as sheep, cattle and goats.

5.1.4 Fynbos

• Includes two key vegetation groups: fynbos and Renosterveld.
• Location: only found in the winter rainfall areas of the Western and southern Cape; nowhere else in the world.
• Climate: rainfall is 400–1 200 mm per year. The summers are hot, with dangers of fire. The winters are cold and wet.
• Flora: mostly bushes with hard leaves. There are also reeds, which look like grass that people use for thatching roofs. There were few trees in the fynbos until people began to plant trees from other areas / countries.
• Fauna: there is little farming with grazing animals on the fynbos, as this veld type is not suitable for grazing. In certain areas people farm sheep and goats.

5.1.5 Nama Karoo (semi-desert)

• The second-largest biome in South Africa.
• Location: western half of the central plateau of South Africa, at altitudes between 500 and 2 000 m, with most of the biome failing between 1 000 and 1 400 m.
• Climate: hot, dry area with little rain in summer (400 mm per year).
• Flora: mostly small, low bushes.
• Fauna: the Nama Karoo is a sheep farming area. Farmers need large areas of land to feed their sheep, because the area is too dry to produce much plant growth.

5.1.6 Succulent Karoo

• This biome has an equal status to the other biomes in South Africa – it is not a subtype of a Karoo biome.
• Location: situated to the west of the Nama Karoo, to the west and south of the central plateau of South Africa, and above the Cape Fold Belt. Namaqualand, famous for veld flowers during spring, falls within this region.
• Climate: very dry with less than 100 mm of winter rain per year. The summers are hot and the winters are mild with no frost.
• Flora: mostly small bushes with stems and leaves that store water (succulents).
• Fauna: this is a sheep farming area.

5. 2 Human impact on the biomes of southern Africa

• Human activities can damage the biomes, for example, pollution, which influences the quality of the water, soil and air. Severe air pollution causes global warming and climate change.
• If a biome is damaged, the biodiversity is damaged as well. Biodiversity is important for healthy crop production.

5.3 Importance of biomes for agriculture
Different forms of agriculture are practised in the different biomes, because each biome has certain characteristics (climate, fauna and flora) that support a particular branch of agriculture. For example:

• The fynbos biome (Western Cape) supports the entire fynbos-producing industry. The bulk of the flowers are exported to Europe, so this industry earns foreign currency for South Africa.
• The grasslands, savanna and the Karoo produce the bulk of animal forage material.
• The forest biome supports the tropical and sub-tropical fruit industry, as well as plantations for the paper and wood industry.

Unit 6: Climate Change and Effects of Weather Phenomena

6.1 Climate change and global warming

• Our planet is presently going through a period of climate change.
• Climate change = long-term change in the distribution of weather patterns over periods of time that range from decades to millions of years.
• There has always been climate change, but our climate change is caused by people and is happening more quickly than previous climate changes.
• In our time, climate change = global warming, because the climate of the Earth is becoming warmer due to human activities.

6.2 Causes of global warming

• The main cause = changes in the gases that make up the air:
  • Normally, the sun heats the Earth during the day; at night the earth cools off.
  • But, the gases from air pollution, especially carbon dioxide, absorb the heat from the sun and thereby prevent cooling at night. (There has been an increase in carbon dioxide in our atmosphere because of industrialisation and the accompanying deforestation.)
  • The result is that the earth is becoming warmer.
• Air pollution is mainly caused by:
  • smoke from coal, wood or veld fires
  • smoke from factories
  • exhaust gases from motor vehicles that burn petrol and diesel
  • smoke from power stations that burn coal.

6.3 Impact of climate change on agriculture

• Causes and effects of global warming are international – every country is affected.
• Some of the effects of climate change on agriculture are:
  •  A rise in sea level: The ice at the North and South Poles is melting and sea levels are rising = a problem especially for island nations and low-lying countries.
  • Inability of species to adapt: If the climate changes quickly, plants and animals may not be able to adapt and could become extinct. Some areas could become unsuitable for the crops and farm animals. Farmers will have to change their choice of crops and animals. However, it will be difficult to predict exactly how the climate will change and therefore how the farming systems should change.
  • Unpredictable seasons: The world’s weather patterns are complex and interdependent. One change may lead to another, and then another, so that the delicate balance is destroyed. Climate changes will affect what crops can grow where, the length of the growing season, and the types of pests that attack them.
• In dry countries, droughts are becoming longer and hotter.
• Rainy seasons have become more erratic and unpredictable.
• In the Northern Hemisphere, rain, wind and storms, as well as floods and other natural disasters, are becoming more frequent.

6.4 Weather predictions and rainfall in South Africa
Scientists try to predict weather for months ahead to help farmers to plan.

6.4.1 El Niño and La Niña

• El Niño = when the temperature of the surface of the sea in the equatorial Pacific Ocean off the South American coast becomes warmer than normal → influences the movement of air → changes global climate patterns. (It happens around Christmas.)
• La Niña = the opposite of El Niño → the sea surface temperatures in the equatorial Pacific become cooler than normal.

El Niño and La Niña influence both rainfall and temperature patterns worldwide. In general, southern Africa receives below-average rainfall during El Niño and above- average rainfall during La Niña. But this = unpredictable → South Africa has a number of different rainfall regions and they are not all affected in the same way (e.g. in 1997–98 El Niño was the strongest on record, but not all of South Africa received below-normal rainfall; some regions received high rainfall due to moist air from the Indian Ocean.

6.5 Short-term climate and weather predictions
Short-term weather conditions (e.g. floods, hailstorms) are predicted by the SA Weather Service. Farmers can take preventive measures based on these predictions.

6.6 Agricultural adaptation measures to overcome climate change

• Climate change creates different conditions: need more comprehensive adaptation measures from those needed for short-term weather conditions. These measures include better land and water management, as well as new agricultural technology.
• Scientists agree that climate change will reduce rainfall, while warmer temperatures will cause plants to need more water. Therefore, rainfall needs to be captured and stored better, e.g. by building stone banks, waterways or vegetation strips.
• Crops and land need to be managed better, for example:
  • fertiliser micro-dosing (fertiliser is applied with the seed when planting it)
  • minimising soil disturbance (no-tillage )
  • crop rotation
  • conservation agriculture
  • using crop varieties that can deal with a greater variation in temperature and less water.

Topic 1: Questions

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

Questions

1. Define ecology? (2)
2. Describe what an agro-ecosystem is. (3)
3. Draw a diagram to show the levels of organisations in an ecosystem. (8)
4. Discuss the physiographic factors in an ecosystem. Explain the influence that each physiographic factor has on an ecosystem. (12)
5. Draw and label a simple a food chain. (5)
6. Describe the five types of interaction that are found in ecosystems. Provide an example of each type of interaction. (15)
7. List the main features of biological farming. (5)
8. What is selective grazing? (3)
9. What is stocking rate? (4)
10. List the three main veld types in South Africa. (3)
11. Name the ten categories that are scored to determine the condition of pasture. (10)
12. Identify the six main types of biomes in South Africa. (6)
13. List the four main causes of global warming. (4)

[Total marks: 70]