Page:Niger Delta Ecosystems- the ERA Handbook, 1998.djvu/82

The Freshwater Ecozone 6.3 PALMS AND OTHER VEGETATION

#


 * Firstly they are monocotyledons, plants that emerge from their seed with a single leaf. (Broad-leaved trees are dicotyledons—plants whose seedlings begin with a pair of leaves).
 * Secondly, palms have only a single stem which does not bear branches.

Palms are one of the few groups of monocotyledonous plants which grow tall enough to be called trees. Monocotyledons are normally shorter, because they do not develop the bark and cork layers that give dicotyledons the physical strength to support a tall plant body. In evolutionary terms, palms are less advanced and need higher light intensities than the broad-leaved trees; they cannot compete with them and are not found in the taller-canopied climax rainforest.

#

These are all related to their fibrous root systems:


 * First, they have adventitious roots at the base of the trunk, parts of which can grow above ground, in some species acting as breathing roots;
 * Second, the root system is a thick, raft-like mat of surface roots that support the palm on a sort of raft, keeping the adventitious roots near the surface of the muddy soils; and
 * Third, this mat of roots, being near the surface, may retain bubbles of oxygen during inundation of floodwater allowing the palm to avoid 'drowning'.

#


 * First, there is little competition as few other species are well adapted to swamp conditions.
 * Second, palm fronds can grow almost vertically allowing individual plants to crowd together without unduly obstructing each other's light, while restricting the development of other plants.

#

The main palm species of the FAM are the oil and raffia palms. For a start, the ecozone is the endemic home of the Oil Palm (Elaeis guineensis), which prefers the drier and lighter ground of swamp margins.

The Raffia Palms (mainly Raphia gigantia, R. hookei and R. vinifera) can tolerate longer periods of water-logged, reduced conditions and even short periods of salinity, if it is low; some Raffia species have breathing peg-roots (Pneumataphores) which makes them even more able to withstand reduced soil conditions.

Rattan palms are found where there are tall broad-leaved trees for them to climb with their sharp hooks. Calamus deerratus is most common to the Delta FAM, with Eremospatha laurentii and E. wendlandiana also being found. (Morakinyo)

Oil and Rattan palms do not grow on the freshwater/brackish water ecotone, but Raffia palms are characteristic. However the stilt-rooted Pandanus palm, Pandanus candalabrum, tends to predominate on the very brackish edge of this ecotone. (Although 80