A n th ro p o g e n ic impacts causing forest fra g m e n ta tio n and affecting
the navigability o f bolongs in the mangrove forests o f Sokone
(Senegal). A geom atic study sup p o rtin g the m anagem ent o f natural
resources
Kungula Makoso D jedje1, Sylvestre Géoris', Katrien Q u isth o u d t1 and Farid Dahdouh-Guebas123
1 Laboratory o f Systems Ecology and Resource Management, Université Libre de Bruxelles - ULB,
Avenue Franklin D. Roosevelt 50, CPI 2 6 4 /1 , B-1050 Brussels, Belgium
E-mail: dkunqula@ ulb.ac.be
2 Laboratory o f Plant Biology and Nature Management. Vrije U niversiteit Brussel - VUB, Pleinlaan 2,
B-1050 Brussels, Belgium
3 This study was in part financed by the Zemst-Sokone city link.
Sokone's mangrove lies in the natural region o f Sine-Saloum in Senegal. It is a delta form ed by tw o
rivers branched into a m ultitu de o f creeks (bolongs) subject to the influence o f the sea and tides
(Lhomme, 1978). Economic activities o f the region: artisanal fisheries, tra n s p o rt and trade o f
mangrove products (wood, oyster, shells,...) depend on m angrove and naviga bility o f bolongs which
is related to the state o f the mangrove. Mangroves in th is region are subject to both natural and
anthropogenic pressures th a t cause degradation. Logging is the main anthropogenic cause o f this
degradation. Wood requirem ents are expected to increase due to population grow th and d e ficit o f
means o f co ntrol and m anagem ent o f natural resources (Géoris et a i, 2014, th is issue).
This study is based on a com bination o f remote sensing and field w ork to id e n tify and examine
more or less disturbed areas caused by logging and sedim entation o f bolongs responsible fo r the
fragm entation, in ord er to conclude if th is m angrove resists to natural and anthropogenic influences
w ith respect to its structure and dynamics.
Mangrove areas as well as points o f sedim ented bolongs were identified on a visual basis o f Google
Earth images, field visits and a survey o f the population. In to ta l 36 quadrats o f 100m 2 each along a
land-water transect have been made. A t each quadrat we recorded tree identity, stem diam eter,
d istrib u tio n o f adult, young and juvenile trees, tree height, salinity, num ber o f cut stems, the X-Y
coordinates o f each a du lt tree and GPS coordinates.
A Detrended Correspondence Analysis (DCA) was applied to inte rp re t the d is trib u tio n o f tree
species in adult, young and juve nile in term s o f present and fu tu re vegetation dynamics while the
species-environm ent relationship was established th ro u g h the canonical correspondence analysis
(CCA). Past dynamics w ill be partly expressed th ro ug h the frequency d is trib u tio n o f diam eter
classes at 2.5cm intervals (Dahdouh-Guebas ex a!., 2002). The CCA results w ill be used to
understand the im pact o f logging on the vegetation structure observed and hence the
anthropogenic impact.
Land cover maps were drawn from Landsat TM 1988 and ETM+ 2007 images and a to po gra ph ic
map at a scale o f 1:50,000 to view the recent occupation o f mangrove and non mangrove.
Sedimented bolongs sectors w ill be related to perim eters o f disturbed vegetation th ro u g h the map
to determ ine if th ey match.
Results may h ig h lig h t a relationship between fo re st fragm entation due to logging and
sedim entation o f bolongs. W herever possible, we w ill id e n tify areas o f urgent conservation and
provide guidelines fo r the restoration a n d /o r e x p lo ita tio n o f o the r areas.
References
Dahdouh-Guebas F. and N. Koedam. 2002. A synthesis o f e xiste n t and potential m angrove
vegetation structure dynamics from Kenyan, Sri Lankan and Mauritanian case-studies. Bull.
Séanc. Acad. Sei. Outre-M er 48 (20 02 -4 ):4 8 7 -5 11.
Dahdouh-Guebas F.,J.G. Kairo, L.P. Jayatissa, S. Cannicci and N. Koedam. 2002. An o rd in a tion study
to view vegetation structure dynamics in disturbed and undisturbed m angrove fo re st in Kenya
and Sri Lanka. Plant Ecology 161(1): 123-135.
Géoris S., D. Kungula Makoso and F. Dahdouh-Guebas. 2014. Are the mangroves o f Sokone (Sine
Saloum, Senegal) utilize d in a sustainable way ? An analysis m erging socio-ecologic interviews
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Lhomme F. 1978. Sénégal, Sine-Saloum, Gambie, Casamance: H ydrographie, pêche crevettière.
Centre de recherches océanographique de Dakar-Thiaroye. ISRA. Archive 66. 29p.
T om linson P.B. 1 986. The botany o f mangroves. Cam bridge (UK):Cambridge U niversity Press.
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