|Auteur||Nfotabong Atheull, Adolphe (firstname.lastname@example.org)|
|Titre||Impact of anthropogenic activities on the vegetation structure of mangrove forests in Kribi, the Nyong river mouth and Cameroon estuary/Impacts des activités anthropiques sur la structure de la végétation des mangroves de Kribi, de l'embouchure du fleuve Nyong et de l'estuaire du Cameroun|
|Département||F408 - Faculté des sciences - Sciences biologiques (email@example.com)|
|Intitulé du diplôme||Doctorat en Sciences|
|Date de défense||2011-09-13|
Bogaert, Jan (Membre du jury/Committee Member)
Drouet, Thomas (Membre du jury/Committee Member)
Fromard, François (Membre du jury/Committee Member)
Godart, Marie Françoise (Membre du jury/Committee Member)
Hardy, Olivier (Président du jury/Committee Chair)
Dahdouh-Guebas, Farid (Promoteur/Director)
Din, Ndongo (Promoteur/Director)
|Mots-clés||Forest structure reconstruction, Environmental changes, Mapping forest structure, Structural dynamics, Mangrove utilization, Spatial pattern analysis|
|Résumé||Mangroves are intertidal ecosystems found along the tropical and subtropical coastlines.
Though globally recognised as ecosystems of ecological, biological and economical
remarkable importance, these ecotone formations are characterised by a continuously
increasing anthropization. However, very little studies have been focused on the impact of
various anthropogenic activities on the mangrove vegetation structure.
We have firstly (a) assessed the commercial and subsistence utilization of mangrove
wood products in the Littoral region (Cameroon estuary). Then, we have confronted the
subsistence usages of mangrove wood products in the Southern region (close to the mouth of
the Nyong River and Mpalla village (Kribi)) in comparison with the Littoral region. By doing,
we have compared the local residents‟ perceptions on environmental changes that occurred
within the two regional mangrove forests. Also, we have (c) studied the structural dynamic of
mangrove vegetation neighbouring the Douala city (Cameroon). Always in the vicinity of this
town, we have (d) reconstructed the original structure of largely disturbed mangrove forests.
Moreover, we have (e) map the mangrove structure in a non peri-urban setting located within
the Cameroon estuary. Here, we have finally (f) analysed the spatial distribution of a black
mangrove namely Avicennia germinans (L.) Stearn.
Our results underlined an excessive utilization of mangrove wood products in the
Cameroon estuary. We have showed that the frequency of mangrove harvesting was relatively
fewer in Kribi (Mpalla) and the mouth of the Nyong River. The local people inhabiting these
two localities perceived mangroves as less degraded areas. In contrast, those established
within the Cameroon estuary stated that mangroves were largely disturbed. When combining
the local people statements with our field observations, we recorded that it a complex mix of
causes (e.i., clear-felled corridors, agriculture, sand and gravel extraction, over-harvesting and
anarchic urbanization) that have led to the largely degradation (vegetation and sediment) of
the peri-urban mangroves in Cameroon. A diachronic analysis (1974, 2003, 2009) of their
coverage revealed that over the 35-year period, mangrove had decreases in cover of 53.16%
around Douala. We have also showed that in the peri-urban settings, wood harvesting was
commonly applied on the structurally more complex (highly dense stands neighbouring the
habitations) mangrove forests (Mboussa Essengue) and, in a lesser extent, on the structurally
more developed mangrove stands (fewer dense stands faraway from Douala). On the other
hand, the mapping analysis of the non peri-urban mangroves (distant from Douala) has
revealed that the structure of these intertidal forests was relatively less impacted. In the
Cameroon estuary, we also showed that A. germinans trees were randomly distributed on
almost one-half of the sampling plots and clumped at some scales on the remaining plots.
Accordingly, this species might play a significant role in the recovery process of artificial
gaps found in the non peri-urban areas.
The multi-disciplinary approach employed in this study has allowed a better
understanding of the direct and indirect impacts of anthropogenic activities on the mangrove
vegetation structure in Cameroon. These results constitute a fundamental data base quite
useful for the multi-temporal monitoring of these littoral ecosystems perpetually disturbed.
The application of similar approach in other mangroves facing high anthropogenic pressures