Nigeria lies in the tropics just above the equator within latitudes 10°N and 14°N. The temperature is high and ranges from 25°C to 32°C. The mean annual rainfall ranges from 500mm in the north to 2500mm in the coastal regions.
The following local biomes are present:
• mangrove swamps
• tropical rain forest
• montane forest
• savanna which can be divided into three belts -- the northern and southern Guinea savannas , the Sudan savanna and the sahelian savanna.
These biomes show a close relationship with the annual rainfall, which is the important climatic factor affecting vegetation in the tropics.
Mangrove swamps :
Mangrove swamps are found in the tropics, along coastal regions and river mouths. In Nigeria, mangrove swamps are found in the delta region of Lagos, bendel, rivers and cross river states.
The climate in mangrove swamp regions is hot and wet throughout the year. The total annual rainfall is heavy, usually above 2500 mm , and the average monthly temperature is around 26°C for nearly all months of the year.
Mangrove swamps are forest of small, evergreen, broad leaved trees growing in shallow, brackish water or wet soil. Many mangrove trees have prop roots and breathing roots. These features enable them to grow well in the soft swampy areas.
Tropical Rain Forests:
Tropical rain forest occur in regions that lur between the equator and latitudes 5° - 10°N and S. The forest areas are mainlybin the lowlands but they also extend up hillslopes to a height of 600 or 900m.
In Nigeria, rain forests cover part of Oyo, bendel, IMO , cross river, Ogun, ondo and river States. Many rain forest areas, however, have been cleared for industrial, agricultural and residential purposes.
The climate in tropical rain forest is hot and wet throughout the year. The mean annual temperature is 27°C while the mean total annual rainfall is 2000mm.
The tropical rain forest is dense and made up of many types of broad leaved tress that are mostly evergreen, I.e. the trees drop their leaves gradually throughout the year, and new leaves grow continuously to replace them. The trees form layers or strata (singular, stratum). The treetops form a thick canopy that prevents sunlight from reaching the forest floor. As a result, the vegetation on the forest floor is sparse. Epiphytic plants and woody climbers known as lianas are common features of these forests.
Montane forest:
This is one of the main biomes of the Nigerian biotic community. It is the biome of the biotic community of mountains.
Montane forests are characterized by low temperatures, high rainfall and high relative humidity. Trees are tall but few and scattered. Grasses form the most predominant biotic community and are closely followed by abundant grazing animals.
Savanna :
Tropical grasslands are often known as Savannas. The savanna is usually flat for miles at a stretch. The main savanna region is on Africa. It forms a broad belt, up to 1000km wide, to the north, east, south of the tropical rain forest region of west Africa and the zaire basin. Other tropical grassland regions are found in south America and Australia.
The west African savanna has three belts: the guinea savanna and the sahelian bordering the desert. In Nigeria, the guinea savanna is found in part of Kaduna, kwara and Benue states; the Sudan savanna, in kano and parts of borno, sokoto, Niger, gongola and bauchi states; and the sahel around lake Chad.
The savanna regions have a hot, wet season which alternates with a cool dry season. The average monthly temperatures are around 29°C during the hot season, and around 18°C during the cool season. The total annual rainfall varies a great deal from around 500mm in regions on the semi desert fringes to about 1500 mm in regions in regions bordering the rain forests. Most of the rain falls during the hot season, I.e from may to October in the west Africa savanna regions.
The rainfall of the savanna is insufficient to support a rich growth of trees but is enough to prevent deserts from forming. Thus, the savanna is mostly dominated by perennial grasses with clumps of trees. In moist guinea savanna, the grasses grow tall during the rainy season. Trees occur quite close together especially along the rain forest fringe. In the drier Sudan savanna, the grass is shorter and the trees are fewer and more scattered. In the sahel which borders the sahara desert, the land is quite bare with clumps of short grass and a few isolated shrubs and trees. During the dry season, the grass is usually dry and brown, and bush fires are common occurrences. The underground parts of the grasses survive the dry season and fires, and grow again when the rains come.
