Diagnostic partiel de la flore et de la végétation des Niayes et du ...

Abstract
Partial diagnosis of flora and vegetation of Niayes and Peanut Basin areas in Senegal:
application of floristic, phyotsociologic, ethnobotanic and mapping methods.
Researches carried out in this thesis about updating flora and vegetation data from two major
agroecological regions of Senegal (Niayes and Peanut Basin) used village-scale based methodology in
order to better consider ligneous resources conservation. In savannas and sub-guinean vegetations of
respectively Peanut Basin and Niayes, 288 records were realized upon stratification method based on
ethnic groups (Wolof, Peul and Sérer), land use systems and topography in 6 villages and 25 records in
the reference sites. In these villages, knowledge, priorisation and uses, prior to sustainable
agrobiodiversity management, were also addressed on 124 ligneous species by ethnobotanic survey with
216 respondants equally distributed to ethnic groups, ages and gender. Respondants also addressed
vegetation dynamics a long topographic position. Informations on land occupation trends were gained
by air-photography cartography and Google earth 2006 image. Factorial experimentation on 3 factors
(species, high and diameter of sprouting) with 15 repetitions was implemented on stump regeneration
dynamics of the 2 principal Combretaceae in the Peanut Basin region (Combretum glutinosum and
Guiera senegalensis). Multivariate and univariate analysis were performed on the data.
Phytosociological results showed discrimination of 11 vegetation groups (G). Two of them (G4 and G8)
are savannas samples, one secondary forest (G10), two from semi-aquatic vegetation (G1 and G5); in
the other hand, two groups of disturbed situations (G6 and G7) and four cultivated and postcultural
groups were found (G2, G3, G9 and G11). The first groups were progressively invaded by cultural and
poscultural species and the second groups by ruderary and adventitious species. Systematic position of
these groups was indicated. 336 species were recorded: 260 in the Niayes and 176 in the Peanut Basin).
Richness in wilderness criterion was not always superior in peul villages.
Ethnobotanical results showed subdivision of species diversity in 4 classes of conservation priority.
Most conservation priority species were multipurpose trees. A clear separation between Niayes villages
and Peanut basin ones, and also between counterparts’ villages was found. Ethnobotanical valuation of
species was higher in the Peanut Basin area. It grows with human density a part from wolof village of
the Peanut basin. Villages of the Groundnut Basin showed no selectivity in the choice of species to meet
their different needs. This lack of selectivity is complete and translates woody resources scarcity.
Cartographic results show an important landscape transformation in Niayes and Peanut basin areas due
to fields creation or aggregation processes running everywhere. This occurred against vegetation
formations : attrition of woody savanna in the two zones, attrition and aggregation of shrubby savanna
in Niayes area, fragmentation and dissection in Peanut basin.
In short term cutting system of the Peanut Basin, it should be better to practise a selective logging
method according to species and diameter classes in order to reconcile productivity and sustainability by
ensuring stumps’ low-stem resprouting.
An extension of terroir approach methodology in other local eco-geographical zones of Senegal should
be tested in order to complete the identification and monitoring of the dynamics of plant communities,
their integration into modern classification to facilitate the monitoring of their spatio-temporal
evolution. It should allow the assessment of species local importance variability.
Keywords: Senegal, Niayes, Peanut-basin, flora, vegetation groups, ethnobotany, spatial dynamics,
forest experimentation.
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