Page:Niger Delta Ecosystems- the ERA Handbook, 1998.djvu/72

The Lowland Equatorial Monsoon Ecozone roots which frequently merging into large spurs or buttresses. However they may or may not have taproots, while the vertical 'sinkers' can be weak or well developed.

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Many of the smaller pioneer trees and trees which grow in Oligotrophic (nutrient-poor) conditions trees are more likely to have many oblique roots and a prominent tap-root.

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Aerial roots are a major feature of tropical rainforest trees, especially when subsurface rooting is impeded by hard soil pans or high water tables (waterlogging). Aerial roots take advantage of above-ground moisture and nutrients as well as giving added physical support to the tree.

Aerial roots of the natural LEM ecosystem will have included buttresses, knee roots (where portions of the root, either the main lateral root or a branch of it, have left the soil, travelled above it and returned to it) and root-knees, which are bumps of intense bark growth (see figure 1.).

Other Aerial roots, common only in the waterlogged sub-ecozones of the LEM tropical rainforest are stilt roots and hanging roots. Both are common in the mangrove tropical rainforests.

The upward growing breather roots or Pneumatophores of some mangrove species are discussed later, under alluvial rainforest (7.3).

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Fibrous roots are most common in waterlogged conditions, and are covered in the discussion on palms, under alluvial rainforest (6.3).

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These are common to many parasites.

A host tree may be smothered by clinging roots or live to an old age, growing happily together with its parasite species for years. There is a good example in the ancient Ficus preserved as a sacred tree in the village square of Botam-Tai.

5.7.2 ARCHITECTURE

The architecture of a tree is defined as much by its roots as by other body parts. However the more immediately visible characteristics of architectural variation are the shapes and branching habits of trunks and crowns.

There are two main types of architecture: branched and unbranched. Branched trees may have branches of equal status where no single branch dominates, or a hierarchical system of branches with varying status.

The great Silk Cotton tree, Ceiba pendantra, which dominates the canopy of the tropical rainforest on the margins of streams and lakes, shows an unbranched habit in its youth (with the typically thorny stem) and a branched habit in its maturity. 70