With relevant sketch maps, discuss the relationship between climate and vegetation in Nigeria.

The relationship between climate and vegetation in Nigeria

There is a close positive relationship between climate and vegetation in Nigeria. The natural vegetation of any belt depends chiefly on the amount of rainfall it receives, the length of its rainy season and its temperature. Because rainfall is heaviest along the southern coast and decreases steadily northward, the vegetation also changes in step: it grades from dense evergreen forest in the wet south, through the savanna grasslands of the middle belt, to sparse, drought-tolerant scrub in the dry far north. As a result the vegetation belts, like the climate belts, run roughly east to west and succeed one another from south to north.

The two sketch maps below place the climate belts and the vegetation belts side by side. Notice that each vegetation belt occupies almost exactly the same position as the climate belt that produces it.

Map 1 – Climate belts

Map 2 – Vegetation belts

How the belts match, from south to north

Explaining the relationship

• Rainfall is the master control. Where rainfall is heavy and falls for most of the year (the south), trees have enough water all year, so the vegetation is a dense, multi-layered evergreen forest. Along the tidal creeks of the Delta the wettest ground carries mangrove swamp forest.
• As rainfall decreases northward, the forest thins. In the middle belt the total rainfall is lower and a real dry season appears, so tall forest gives way to Guinea savanna – a mix of tall grasses and fire-resistant trees.
• A longer, harsher dry season in the north (with the dry, dusty Harmattan) allows only grasses and scattered thorn trees to survive: this is the Sudan savanna, and in the driest north-east it becomes the open Sahel savanna of short, sparse grass and thorn scrub.
• Temperature and evaporation reinforce rainfall. The hot, dry north loses much water by evaporation, worsening the moisture shortage and favouring drought-tolerant, deep-rooted plants over tall broad-leaved trees.

Conclusion: the heavier and longer the rainfall, the thicker and taller the vegetation. Because rainfall falls steadily from the wet south to the dry north, the vegetation belts change in the same direction – from mangrove and rain forest, through Guinea and Sudan savanna, to Sahel scrub. The two sketch maps therefore show the same belts lying in the same places, proving the direct relationship between climate and vegetation in Nigeria.