Basic Ecological System II SS1 Biology Lesson Note

BIOMES

Biomes are large natural terrestrial ecosystems, identified by their dominant vegetation. They are terrestrial because plants form the bulk of the community in any ecosystem e.g. a forest biome has densely packed tall trees while grasses and few scattered shrubs are found in a savanna biome. Climatic factors determine the type of vegetation in a biome. These factors may include rainfall, relative humidity, temperature, wind and light.

LOCAL BIOMES

The local biomes particular to Nigeria include the following:

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

1. MANGROVE SWAMPS

These are found in the tropics along coastal regions and river mouths. Mangrove swamps are forests of small, evergreen, broad-leaved trees growing in shallow, brackish water or wet soil. Many mangrove trees have pop roots and breathing roots called pneumatophores. The climate here is hot and wet, with a total annual rainfall of above 250cm and a temperature of about 260c. In Nigeria, mangrove swamps are found in the delta region of Lagos, Delta, Rivers, Bayelsa and Cross Rivers states.

2.TROPICAL RAIN FOREST:

This occurs in the region that is between the equator and latitude 50-100N 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 their 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 200cm and 270c respectively.

In Nigeria, tropical rainfall is found in Edo, Delta, Ondo, Imo, Lagos, Rivers State etc.

3. SAVANNA

These are tropical grasslands in Africa. They are usually flat for miles at a stretch and made up mainly of grasses. The savanna region has hot and wet seasons (290c) which alternate with a cool and dry season (180c). The total annual rainfall is around 50cm-150cm. During the dry season, the grasses are usually dry and brown and bush fire is a common occurrence. 

i. South Guinea savanna (the largest of all the biomes in Nigeria) has tall grasses with scattered, deciduous trees. It is found in Enugu, Kogi, Benue, Kwara, Oyo, Osun, Ekiti State etc.

ii. Northern Guinea Savanna has scattered, deciduous trees, sometimes with thorns and tick barks. Grasses are short and numerous. it is found in Plateau, Kaduna, Bauchi, Niger, Kano, Adamawa states etc.

iii.  The Sudan savanna has shorter grasses and fewer trees which are more scattered. It is found in Kano and parts of Borno, Sokoto, Niger, Bauchi states e.t.c

 iv.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, Kastina, Sokoto, Yobe, Kano, Jigawa states etc.

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.

1. TEMPERATE FORESTS

These are forests with the following characteristics they are:

1. Mainly of broad-leaved deciduous trees which shed their leaves during winter.
2. Possession of a moderately wet climate with a dry or cold season.

2. CONIFEROUS FORESTS

These are characterized by:

i. Needle-leaved evergreen conifers such as pines, and firs.

ii. Possessing a few trees.

iii. Possessing tall tree forming upper storey.

iv. The forest floor is covered with a thick layer of conifer needles.

v. Possessing a cool temperature climate with light rainfall and snow.

3. TEMPERATE SHRUBLAND

This is a forest with the following characteristics:

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

4. TEMPERATE GRASSLAND

This is characterized by:

1. Perennial grasses grow on very fertile soil to support herds of grazing mammals
2. It has a moderately dry climate with a cold winter and a hot summer

5. SAVANNA

This is a tropical grassland with: 

1. Scattered trees and often infertile soil
2. Moderately dry climate with a warm dry season and a hot rainy season

6. DESERT

This has:

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

7. TUNDRA

This is characterized by:

1. Treeless marshy vegetation composed mainly of dwarf shrubs, grasses, lichen and moss with very few plant trees.
2. Cold climate with long icy winter and very short summer with an average temperature of 100c.

8. MOUNTAIN VEGETATION

This has:

1. Evergreen rainforests on slopes of mountains, these forests are less luxuriant than the tropical rainforest.
2. Afro-alpine vegetation occurs at heights above 3000m on mountains, vegetation consists mainly of heath, grasses and sedges.

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 300m 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.