Geoscience Reference
In-Depth Information
large edible fruits and nutritious seeds, the majority of which are destroyed by
invertebrates. These fruits and seeds are crucial to the survival of animals in the for-
est. In turn, animals are critical for the germination and dispersal of many of these
seeds. Although insects pollinate most African rainforest plants, 75 percent of their
seeds are dispersed by mammals, birds, and fish.
Many of the seeds of the African rainforest are covered by hard shells and sur-
rounded by fruits enclosed in tough casings. Vertebrates eat many of these fruits.
Indeed some seeds need to go through an animal's digestion system to break the
seedcoat for germination. The makore tree, for example, is dependent on forest ele-
phants to crush the large, hard seed case and consume the seeds. The elephants effi-
ciently disperse the seeds that easily germinate in their dung.
Some African rainforest trees and lianas exhibit cauliflory, where flowers and
fruits grow from the trunk rather than off tree branches. False kola is an African
tree displaying cauliflory. Several figs also exhibit cauliflory.
Vines are an important structural feature within the African rainforest and the
leaves and fruit are a food source for animals. The African rainforest is relatively
poor in lianas compared with its regional counterparts. Several plant families,
including the legume and coffee families as well as dogbane (Apocynaceae), squash
(Cucurbitaceae), morning glory (Convolvulaceae), milkweed (Asclepiadaceae),
knotweed (Polygonaceae), among others have lianas and vine species. Fig trees are
common stranglers in the African rainforest as well as other tropical forests of the
world, using their host trees for structural support.
Epiphytes are present in the African rainforest, but diversity and abundance is
less than in the other rainforest regions. At least twice as many genera and species
are found in the Neotropical and Asian-Pacific rainforests. The lower number of
epiphytes correlates to the relatively lower rainfall amounts in this region as well as
to the limited areas of rainforest. African epiphytes consist primarily of orchids and
ferns with a notable absence of the bromeliads so common in the Neotropics. More
than 100 epiphytic species have been identified within the African rainforest.
Orchids are relatively abundant in the African rainforest, with about 15 percent of
the world's orchid species occurring here.
Swamp Forests
The swamp forests of the Niger and Congo Delta are the largest such habitats in
Africa. Precipitation is high at 100-160 in (2,500-4,000 mm) on average, with an
average annual temperature of 82
C). Hydrology determines species com-
position within the swamp forests. Flooded forests occur in lower-salinity areas
behind mangroves, along rivers, and in low areas of poor drainage. Species in these
areas depend on the depth, frequency, and duration of flooding. Many flooded for-
ests are dominated by one species. Plants of the flooded forest typically have large
seeds that float to facilitate dispersal and germination. Fish living within these
flooded forests assist in these processes. The threatened Niger Delta pygmy hippo,
crested genet, and chimpanzee are found in these forests.
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