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

What are biomes?

Biomes are large natural terrestrial ecosystems, identified by their dominant vegetation. Plants form the bulk of the community in any ecosystem, so each biome is named after its main plant cover. For example, a forest biome has densely packed tall trees, while grasses and a few scattered shrubs are found in a savanna biome. Climatic factors determine the type of vegetation in a biome. These factors include rainfall, relative humidity, temperature, wind and light.

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 are the local biomes of Nigeria?

The local biomes particular to Nigeria are:

1. Mangrove swamp
2. Tropical rainforest
3. Savanna (Northern and Southern Guinea savanna, Sudan savanna and Sahel savanna)

Mangrove swamps

Mangrove swamps are found in the tropics along coastal regions and river mouths. They are forests of small, evergreen, broad-leaved trees growing in shallow, brackish water or wet soil. Many mangrove trees have prop roots and breathing roots called pneumatophores.

The climate is hot and wet, with a total annual rainfall of above 250 cm and a temperature of about 26°C. In Nigeria, mangrove swamps are found in the delta region of Lagos, Delta, Rivers, Bayelsa and Cross River states.

Tropical rainforest

The tropical rainforest occurs in the region between the equator and latitude 5° to 10° N and S. It has the following characteristics:

• The forests are mainly lowland.
• The climate is hot and wet.
• It consists of broad-leaved trees that are mostly evergreen. The leaves are gradually shed throughout the year and replaced by new ones.
• The trees form canopy strata, with the interior having low light intensity, high humidity and damp floors.
• The trees possess thin bark.
• The forest is rich in epiphytes and wood climbers.
• The annual rainfall and temperature are 200 cm and 27°C respectively.

In Nigeria, the tropical rainforest is found in Edo, Delta, Ondo, Imo, Lagos and Rivers states, among others.

Savanna

Savannas are tropical grasslands in Africa. They are usually flat for miles at a stretch and made up mainly of grasses. The savanna region has a hot, wet season (29°C) which alternates with a cool, dry season (18°C). The total annual rainfall is around 50 cm to 150 cm. During the dry season, the grasses are usually dry and brown, and bush fire is a common occurrence.

Nigeria has four types of savanna:

1. Southern Guinea savanna is the largest of all the biomes in Nigeria. It has tall grasses with scattered, deciduous trees. It is found in Enugu, Kogi, Benue, Kwara, Oyo, Osun and Ekiti states, among others.
2. Northern Guinea savanna has scattered, deciduous trees, sometimes with thorns and thick barks. Grasses are short and numerous. It is found in Plateau, Kaduna, Bauchi, Niger, Kano and Adamawa states, among others.
3. Sudan savanna has shorter grasses and fewer trees, which are more scattered. It is found in Kano and parts of Borno, Sokoto, Niger and Bauchi states, among others.
4. Sahel savanna has high temperatures and low rainfall, with short and scanty grasses as well as short and tough shrubs or trees. The plants are drought-resistant. It is found in Borno, Katsina, Sokoto, Yobe, Kano and Jigawa states, among others.

What are the world biomes?

Of all abiotic factors affecting ecological systems, temperature and rainfall determine the world’s biomes. The biomes include tropical rainforest, temperate forest, coniferous forest, temperate shrubland, savanna, temperate grassland, desert, tundra and mountain vegetation.

Temperate forests

Temperate forests have the following characteristics:

• They consist mainly of broad-leaved deciduous trees, which shed their leaves during winter.
• They have a moderately wet climate with a dry or cold season.

Coniferous forests

Coniferous forests are characterised by:

• Needle-leaved evergreen conifers such as pines and firs.
• A few trees.
• Tall trees forming an upper storey.
• A forest floor covered with a thick layer of conifer needles.
• A cool temperate climate with light rainfall and snow.

Temperate shrubland

Temperate shrubland has the following characteristics:

• It consists of drought-resistant shrub plants and dwarf trees, often fire-resistant, e.g. maquis.
• It has a temperate climate with low rainfall.

Temperate grassland

Temperate grassland is characterised by:

• Perennial grasses growing on very fertile soil, which support herds of grazing mammals.
• A moderately dry climate with a cold winter and a hot summer.

Savanna

The savanna is a tropical grassland with:

• Scattered trees and often infertile soil.
• A moderately dry climate with a warm dry season and a hot rainy season.

Desert

The desert has:

• Very sparse vegetation, with succulent perennials that have deep root systems.
• Tropical, temperate and afro-alpine regions with less than 25 cm annual rainfall.

Tundra

The tundra is characterised by:

• Treeless marshy vegetation composed mainly of dwarf shrubs, grasses, lichen and moss, with very few trees.
• A cold climate with a long icy winter and a very short summer, with an average temperature of 10°C.

Mountain vegetation

Mountain vegetation has:

• Evergreen rainforests on the slopes of mountains. These forests are less luxuriant than the tropical rainforest.
• Afro-alpine vegetation at heights above 3000 m on mountains. This vegetation consists 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

1. How are savanna plants protected from bushfires? They have A. sunken stomata B. thorn bark C. thick barks D. soft leaves
2. Which of the following limiting resources is competed for by organisms in the desert? A. Light B. Oxygen C. Temperature D. Water
3. Which of these is not a true characteristic of the tropical rainforest? A. Vegetation consists predominantly of tall trees with thick canopies B. Forest is rich in epiphytes and climbers C. Annual rainfall is less than 100 cm D. Annual temperature is 27°C
4. Which of the following does not describe the coniferous forest? A. Needle-leaved evergreen conifers B. Broad-leaved evergreen conifers C. Possessing few trees D. Possessing cool temperate climate
5. Montane vegetation is described by the following except A. treeless marshy vegetation B. evergreen rainforest on slopes of mountain C. forest is less luxuriant than tropical rainforest D. afro-alpine vegetation at heights above 3000 m on mountain
6. Outline the properties of the savanna as a world biome.
7. State four characteristic features of vegetation found in A. savanna B. tropical rainforest C. desert.