Basic Ecological System II – SS1 Biology Lesson Note (Second Term)

A biome is a large natural land (terrestrial) ecosystem identified by its dominant vegetation.

Behavioural objectives

By the end of the lesson, students should be able to:

1. Define a biome and state the climatic factors that determine it.
2. Name the local biomes of Nigeria and the states where they are found.
3. Describe the characteristics of the mangrove swamp, tropical rainforest and savanna.
4. List the world biomes.
5. Describe the vegetation and climate of each world biome.

What determines a biome?

Climate determines the type of vegetation in a biome, and the vegetation gives the biome its name.

• Plants: they form the bulk of the community in any ecosystem, so each biome is named after its main plant cover.
• Forest biome: has densely packed tall trees.
• Savanna biome: has grasses and a few scattered shrubs and trees.

Climatic factors that determine a biome

• Rainfall: the amount of water falling in a year.
• Relative humidity: the amount of water vapour in the air.
• Temperature: how hot or cold the region is.
• Wind: affects water loss from plants and the spread of fruits and seeds.
• Light: the amount of sunlight reaching the plants.

What are the local biomes of Nigeria?

Nigeria has three local biomes: mangrove swamp, tropical rainforest and savanna.

What is a mangrove swamp?

A mangrove swamp is a forest of small, evergreen, broad-leaved trees growing in shallow, brackish water or wet soil.

• Location: the tropics, along coastal regions and river mouths.
• Prop roots: roots that grow from the stem and support the tree in soft mud.
• Pneumatophores: breathing roots that grow upwards out of the mud to take in air.
• Climate: hot and wet, with total annual rainfall above 250 cm and a temperature of about 26°C.
• Nigerian states: the delta region of Lagos, Delta, Rivers, Bayelsa and Cross River.

What is a tropical rainforest?

A tropical rainforest is a hot, wet forest of tall, mostly evergreen, broad-leaved trees found near the equator.

• Location: the region between the equator and latitude 5° to 10° N and S.
• Land: the forests are mainly lowland.
• Climate: hot and wet, with annual rainfall of 200 cm and a temperature of 27°C.
• Leaves: the trees are broad-leaved and mostly evergreen. Leaves are shed gradually through the year and replaced by new ones.
• Canopy strata: the trees form layers. The interior has low light intensity, high humidity and damp floors.
• Bark: the trees possess thin bark.
• Epiphytes and climbers: the forest is rich in epiphytes (plants that grow on other plants for support) and wood climbers.
• Nigerian states: Edo, Delta, Ondo, Imo, Lagos and Rivers, among others.

What is a savanna?

A savanna is a tropical grassland, usually flat for miles at a stretch and made up mainly of grasses.

• Location: tropical Africa.
• Climate: a hot, wet season (29°C) alternates with a cool, dry season (18°C).
• Rainfall: total annual rainfall is around 50 cm to 150 cm.
• Dry season: grasses are dry and brown, and bush fire is common.

What are the types of savanna in Nigeria?

Nigeria has four types of savanna: Southern Guinea, Northern Guinea, Sudan and Sahel.

• Southern Guinea savanna: the largest biome in Nigeria, with tall grasses and scattered deciduous trees. Found in Enugu, Kogi, Benue, Kwara, Oyo, Osun and Ekiti, among others.
• Northern Guinea savanna: scattered deciduous trees, sometimes with thorns and thick barks, and short, numerous grasses. Found in Plateau, Kaduna, Bauchi, Niger, Kano and Adamawa, among others.
• Sudan savanna: shorter grasses and fewer, more scattered trees. Found in Kano and parts of Borno, Sokoto, Niger and Bauchi, among others.
• Sahel savanna: high temperatures, low rainfall, short and scanty grasses, and short, tough shrubs or trees. The plants are drought-resistant. Found in Borno, Katsina, Sokoto, Yobe, Kano and Jigawa, among others.

How do the local biomes compare?

The three local biomes differ mainly in rainfall, temperature and plant cover.

What are the world biomes?

There are nine world biomes: tropical rainforest, temperate forest, coniferous forest, temperate shrubland, savanna, temperate grassland, desert, tundra and mountain vegetation.

• Main factors: of all abiotic factors affecting ecological systems, temperature and rainfall determine the world’s biomes.
• Tropical rainforest: described above under the local biomes.

What is a temperate forest?

A temperate forest is a forest of broad-leaved deciduous trees in a moderately wet climate.

• Trees: mainly broad-leaved deciduous trees, which shed their leaves during winter.
• Climate: moderately wet, with a dry or cold season.

What is a coniferous forest?

A coniferous forest is a forest of needle-leaved evergreen trees in a cool temperate climate.

• Trees: needle-leaved evergreen conifers such as pines and firs.
• Variety: few tree species.
• Structure: tall trees form an upper storey.
• Forest floor: covered with a thick layer of conifer needles.
• Climate: cool temperate, with light rainfall and snow.

What is temperate shrubland?

Temperate shrubland is a biome of drought-resistant shrubs and dwarf trees in a temperate climate with low rainfall.

• Plants: drought-resistant shrubs and dwarf trees, often fire-resistant, for example maquis.
• Climate: temperate, with low rainfall.

What is temperate grassland?

Temperate grassland is a biome of perennial grasses in a moderately dry climate.

• Plants: perennial grasses growing on very fertile soil, which support herds of grazing mammals.
• Climate: moderately dry, with a cold winter and a hot summer.

What is the savanna as a world biome?

The savanna is a tropical grassland with scattered trees.

• Plants: grasses with scattered trees.
• Soil: often infertile.
• Climate: moderately dry, with a warm dry season and a hot rainy season.

What is a desert?

A desert is a biome with very sparse vegetation and less than 25 cm of rainfall a year.

• Plants: very sparse vegetation, with succulent perennials that have deep root systems.
• Regions: tropical, temperate and afro-alpine.
• Rainfall: less than 25 cm a year.

What is tundra?

Tundra is a cold, treeless biome with marshy vegetation.

• Plants: dwarf shrubs, grasses, lichen and moss, with very few trees.
• Climate: cold, with a long icy winter and a very short summer.
• Temperature: the average summer temperature is about 10°C.

What is mountain vegetation?

Mountain vegetation changes with height, from evergreen rainforest on the slopes to afro-alpine plants near the top.

• Lower slopes: evergreen rainforests, less luxuriant than the tropical rainforest.
• Afro-alpine zone: above 3000 m, made up mainly of heath, grasses and sedges.

Evaluation

1. What is a biome?
2. Name the three local biomes of Nigeria.
3. State three characteristics of the tropical rainforest.
4. Name two features of mangrove trees.
5. List the world biomes.

Assignment

Outline the properties of the savanna as a world biome. Then state four characteristic features of the vegetation of the tropical rainforest.