Page:Niger Delta Ecosystems- the ERA Handbook, 1998.djvu/63

The Lowland Equatorial Monsoon Ecozone Rainfall as a 'limiting factor' is also complex. Research in Amazon rainforests has shown that they reach their maximum height, not in the wettest zones, but in zones adjacent to forest savannah (where limited rainfall reduces tree population to a degree that grasses dominate ground cover). Excess rainfall seems to limit the growth of rainforest trees especially where drainage is limited, as seen in the river flood plains and swamps throughout the Niger Delta: rainforest plants, like most others, prefer dry feet.

There are essentially three major ecozones of the tropical rainforest biome: Lowland, Alluvial and Montane. Lowland and Alluvial rainforest would be the general case in the Delta, but there is no land of sufficient height for Montane tropical rainforest.

Tropical rainforests are not easy to study, which is why so much less is known about their ecosystems than about many others. Three reasons for this express the complexity of the rainforest.

Firstly, the sheer dimensions of tropical rainforest are a problem. A meaningful sample area must cover square kilometres; vertically, access must be gained to intermediate levels and to the canopy which may be over 30m high, then root systems must be followed as far as 5m down through a soil that is hard and crammed with vegetable life.

Secondly, the life span of the dominant life forms (mainly trees) makes for observation periods that exceed human life spans.

And thirdly, the high diversity of plants and animals is daunting; a square kilometre of natural Nigerian rainforest will contain thousands of plant species and countless more animal species.

5.3 CORRECTING SOME MISCONCEPTIONS ABOUT THE RAINFOREST

These points will help in understanding the descriptions and ideas that follow.

5.3.1 THE TROPICAL RAINFOREST IS NOT AN IMPENETRABLE JUNGLE

Rarely is the natural tropical rainforest a nightmare 'jungle' of vines and thick undergrowth. More often the dense tree canopy above ensures that light intensity on the 61