An extension of moist evergreen rainforest (Anhuf
1994) reaching a latitude of 7-7.30°N in the western Ivory Coast
and the area of Sokoto in Togo can be assumed. The highlands of Guinea
up to the southern border of Guinea Bissau (11°N), the eastern part
of the Guinea Coast (up to Lokoja and Makurdi in Nigeria) and the entire
Congo-Basin was covered by this forest type.
Only in the Southeast, (i.e. Angola), more drier humid forest types
occurred. All in all the humid forest zone (evergreen and semi-deciduous)
in West Africa extended up to 12°N (Gambia) and eastward of the prime-meridian
up to 10°N. Semi-deciduous forests could even be found in the East
African Highlands around Lake Victoria. The east African High-Mountain
ridges were covered by a vegetation comparable to today’s. From the climatic
viewpoint, the conditions were probably more humid. The mountains along
the Western Rift Valley were generally more humid than the mountains along
the Eastern Rift Valley (Runge
& Runge 1998). All lakes on the East African Highland were characterized
by highest lake levels within the last 20,000 years.
Likewise the Horn of Africa (Somalia) was distinctly more humid. A
strong summer monsoon was developped because of the maximal summerly insolation
on the northern hemisphere during the Early Holocene. This summer monsoon
caused clearly higher precipitation. Consequently, savannah woodland
and open dry forests could grow in today’s desert areas.
Continuing to the north, dense dry forests became dominant. In the
west of the continent the border of the semi-deciduous rainforests to the
dense dry forests lies in the area of today’s Gambia. In contrast, the
same border is lowered to 11°N in the East. Dense and open dry forests
dominated the floristic Sudanian zone.
The border from dense to open dry forests was situated at about 14°N
(today at 11°N). The edaphic caused grassland of the Niger-interior
delta is also thought to have expanded significantly (Petit-Maire
et al. 1987). Lake Chad covered an area of 330,000 km² that days (Pachur
& Altmann 1997). East of the lake the occurence of extensive periodically
inundated grass savannahs was caused by the tributaries to the Mega-Chad
or as well by the enormous extension of the Nile-Swamps in the Republic
of Sudan.
The transition from open dry forests to tree savannahs was located
at 19°N in the central part of West Africa. The northern Sudanian/Sahelian
tree and grass savannahs extended to the north to the Tropic of Cancer
(Schulz
1987).
Between 19° and 20°N a gradual change to dominant Saharan savannahs
proceeded, whereas at 20°N already there was an obvious border of diffuse
tree/grass savannah to Saharan desert vegetation. However, this desert
vegetation is supposed to have been more dense than today. The eastern
Sahara lost their extreme aridity and numerous rivers crossed the desert
area. The Wadi Howar and Wadi Melik in Sudan became tributaries of the
Nile and around Wadi Howar a tree savannah established. Continuing to the
north tropical and Mediterranean floristic elements mixed up with higher
annual precipitation of about 300 to 400 mm (Ritchie
et al. 1985). In the western and central Sahara a northward shift
of the Saharan-Sahelian border by 2 to 3 degrees occurred (Schulz
1987, 1991,
Schulz et
al. 1990). The annual precipitation amounted
to 100 mm where today 10 to 20 mm per year are registered.
The high mountain areas of Hoggar and Tibesti generated far outbranching
periodic river systems to the North and South. They marked the southernmost
limit of the shift of Mediterranean vegetation forming various altitudinal
belts.
The vegetation cover of north-western Tunisia and parts of eastern
Algeria around 8,000 yr BP can be stated as follows: altitudes between
800 and 1,200 m asl were dominated by cedar forests (Cedrus atlantica).
In drier southern expositions open forests of Pinus halepensis and
Quercus
ilex appeared. The altitudes between 400 and 800 m asl were covered
by deciduous oak forests (Q. canariensis). The area between 200
and 400 m asl was dominated by Q. canariensis and Q. suber.
Below 200 m asl Q. suber was replaced by Q. coccifera (Ben
Tiba & Reille 1982). In the Southern parts areas below 700 m asl
and the Moroccan Lowlands were characterized by steppes with Stipa tenacissima
and numerous other grasses. Evergreen forests of Q. ilex , Q. suber,
and Q. coccifera were distributed along the coast and in lower mountainous
areas between 500 and 1,000 m asl. Along the southern fringe of the Atlas
Mountain the evergreen species were mixed with Mediterranean coniferous
species like pine and fir, as well as with grasses. The Tunisian Basin,
the Sahel of Sousse, Sfax, and Kairouan and the steppe-zone of the south-western
Tunisian and Algerian hills were dominated by shrubs, comparable to southern
France’ maquis.
Go to data-base for 8,000 yr BP
© 2000 Department of Physical Geography, University of Mannheim
Editor: Birgit Schröder