Summary
The implementation of large dams in the late 80s, has led
changes in hydrology, water quality in the delta of the Senegal River and Lake
of Guiers. The new conditions caused changes in the flora and vegetation, and
led the proliferation of aquatic macrophytes such as Typha
domingensis, Potamogeton schweinfurthii, Pistia stratiotes
and Salvinia molesta.This new situation has had some negative
impact on ecology, people, socio-economic and health. The present work was
undertaken to gather information that can contribute to a better knowledge of
the flora, vegetation, biology and ecology of major macrophytes. These data are
essential elements for sustainable management of aquatic macrophytes and
environmental of the Senegal River delta and Lake of Guiers.
Systematic inventory of vascular flora has identified 151
species distributed in 102 genus and 47 families. Monocots represent 41.7% and
dicots 56.2%. The most represented families are Poaceae, Cyperaceae, Fabaceae
and Amaranthaceae. Species diversity is highest in low-lying areas liable to
flooding, due to strong artificial and heterogeneity of these environments,
compared to those of Lake of Guiers and the river. This flora consists
approximately half (55%) of therophytes, phanerophytes and chamaephytes
representing the land component, and half (44.5%) aquatic macrophytes including
helophytes (helogeophytes and helotherophytes) (27%) are more important than
hydrophytes sensu stricto formed by hydrogeophytes, submerged free
hydrophytes, hydrotherophytes hydrohemicryptophytes (17.5%) in varying
proportions depending on the lake, river and flood low-lying areas.These
hydrophytes sensu stricto, although relatively less important, is
nevertheless remarkable floristic elements with families and often
monogeneriques, monospecific characteristics of aquatic environments such as
Alismataceae, Hydrocharitaceaee, Lemnaceae, Najadaceae, Potamogetonaceae in
monocotyledons, Avicenniaceae, Ceratophyllaceae, Lentibulariaceae,
Menyanthaceae, Nymphaceae and Rhyzophoraceae in dicots.
A typology of 48 common species of wetland was established
following four main types: fixed emerging macrophytes, floating macrophytes
fixed, submerged macrophytes and free floating macrophytes. The presentation of
each species could be a tool for identification and information on synonyms,
botanical characters, distribution and ecology of the taxa. Species with wide
geographical distribution, pantropical, paleotropical and cosmopolitan
represent 3/5 of species, compared to strictly african taxa or
Sudano-Guinean-Zambezian and Asian (38%). These species are relatively
homogeneous characteristics and are well adapted to the aquatic environment
which absorbs major ecological changes such as climate.
The study of vegetation, with the transect method, shows that
there is a zonation of vegetation depending on salinity, slope of water level
and duration of flooding: the typhaie on shore, in deeper water pondweed and
between the two, in front of the nymphaea, Typha, direction of prevailing
winds, waves or local mesological conditions, floating plants like Pistia
and Salvinia or fixed plants as Phragmites autralis,
Cyperus articulatus and C. alopecuroides.
The analysis of plant communities, by phytosociological
technique has identified 9 plant groups, which are divided into vegetation of
salty environment and fresh water, their floristic composition were specify and
physionomy. The vegetation of saline environments includes Tamarix
senegalensis and Arthrochnemum macrostachyum. That of freshwater
has from deeper water towards upper parts of the banks, Azolla
pinnata, Potamogeton octandrus, Cyperus alopecuroides,
C. articulatus, Bolboschoenus maritimus, Phragmites
australis, and T. domingensis.
The study of some aspects of the biology and ecology of
proliferating macrophyte indicates that reproduction is primarily vegetative in
P. stratiotes, and P. schweinfurthii whereas in T.
domingensis, it is both vegetative and sexual. These modes give T.
domingensis much power for colonization. S molesta has only
vegetative multiplication.
In total, this work assess the actual situation of the
vascular flora, vegetation and macrophytes in the Senegal river, various
wetlands in the Delta and the lake of Guiers. This reference is essential for a
scientific monitoring of biodiversity and vegetation dynamics. Data on the
biology and ecology of key species could help the recovery, design and
implementation of appropriate control methods of aquatic macrophytes and
sustainable management of Senegal river delta and Lake of Guiers.
Key words: vascular flora, vegetation, macrophyte
proliferation, Senegal river, lake of Guiers.
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