Page:Niger Delta Ecosystems- the ERA Handbook, 1998.djvu/71

The Lowland Equatorial Monsoon Ecozone #

Where fallen trees allow sunlight to penetrate the lower levels of the forest, luxuriant growth of climbers and herbs is stimulated. Dormant seeds germinate and existing tree seedlings and saplings are encouraged to grow faster.

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Were a gap phase is beginning to be filled in by new growth and darken again.

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Along substantial rivers and bordering on lakes, there may be a dense barrier of euphotic plants.

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Along narrower rivers or river sections, seasonal and permanent swamp communities of plants such as such assuch as [sic] palms, bamboo and stilt-rooted broad-leaved trees may develop. (These are described in more detail in Chapter 6.)

5.7 DIVERSITY OF TREE FORMS IN THE LEM RAINFOREST

A wide diversity of tree forms have evolved to suit the varying climatic, topographical and drainage conditions within the LEM rainforest, as distinct from those of the FAM and BAM ecozones. They can be considered in terms of the following parameters:

5.7.1 ROOTS

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 * Tap roots, grow vertically down into the soil. Tap root systems are less common in the tropical rainforest than in the temperate forest, partly because nutrients are concentrated in the surface layers of soil and partly because deep roots are also unnecessary as far as seeking for water is concerned. The physical work of anchoring the plant that is another function of deep taproots is often carried out by aerial or buttress roots to compensate.
 * Lateral roots, which grow horizontally.
 * Fibrous roots which form thick interwoven mats as in palm trees.
 * Aerial roots, which grow in the air.

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With the exception of the palms, which have exclusively fibrous root, a typical tropical rainforest tree tends to have a combination of root types, following one of four patterns:


 * Thick horizontal surface roots, frequently merging into large spurs or buttresses, with no taproots and only weak vertical 'sinkers'.
 * Thick horizontal surface roots, and well-developed taproots and sinkers.
 * Weak surface roots, but a rich system of many oblique roots and a prominent taproot.
 * Numerous sizeable aerial roots, plus a network of weaker underground roots.

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Emergent trees are those that rise to become part of the canopy and which therefore dominate the tropical rainforest. These trees all tend to have thick horizontal surface 69