Mangroves de l’estuaire du Rio Del Rey : conservation, séquestration du carbone et enjeux socio-économiques.

Abstract

Mangroves are edaphic plant formations, which develop in intertidal zone and constitute one of the components of marine and coastal ecosystem. Generally found in estuaries, deltas and bays of tropical regions, mangrove ecosystems constitute a natural heritage due to their biological richness and their functions. Mangroves procure food for the subsistence of populations, participate in water regulation, constitute natural habitats for many animal and plant species and also contribute to carbon sequestration. In view of the remarkable potential offered by mangroves, the conservation of these ecosystems is a necessity. The general objective of this study is to determine the state of conservation of the mangrove swamp in the Rio del Rey estuary in southwest Cameroon.The methodology adopted for this purpose consisted in carrying out plant inventories through the transects, assessing carbon stocks using allometric equations and carrying out socio-economic surveys. Indeed, the inventory was carried out on 14 rectangular plots of 50 mx 100 m, thus a total surface of 7 ha. The results obtained made it possible to show that there are 15 species distributed in 14 genera and 11 families. For ligneous plants, the density is 2758 stems/ha and the basal area of 45.86 m2/ha. This mangrove is marked by a diversity of species with the Shannon-Weaver index equal to 1.81. The densest species are Rhizophora racemosa (44.69 individuals/ha), R. mangle (30.58 individuals/ ha) and Avicennia germinans (20.81 individuals/ha). They are also the most dominant with respectively relative dominances of 48.71%; 32.84% and 16.49%. Rhizophora mangle (48.71%), R. racemosa (32.84%) and Avicennia germinans (16.49%) are species also the most dominant.The family of Rhizophoraceae (IVF = 171.11) and Rhizophora racemosa (IVI = 95.72) are the most important families and species respectively. The mangrove of the Rio del Rey estuary is characterized by 04 plant communities. At the level of the external high mangrove at the borders of the estuary are found Rhizophora racemosa and Pandanus candelabrum group (Gr 1).TheAcrostichum aureum,Rhizophora racemosa, R. mangleandAvicennia germinans group (Gr 2)corresponds to the vegetation of transition zone between mangrove and mainland. As for Raphia palma-pinus, Rhizophora racemosa, R. mangleand Avicennia germinans plant group (Gr 3), it is found in intermediate zone of brackish waters. In the peripheral zone of mangrove by mainland, reached by high tides, are found Avicennia germinans,Rhizophora racemosa, R. mangle and Conocarpus erectus plant group (Gr 4). On the other hand, results on the estimation of carbon storage show that the Rhizophora mangle(301.13 t C/ha),R. racemosa(126.39 t C/ha)and Avicennia germinans (46.63 t C/ha) species have high carbon storage potential. They are capable of rapidly developing. Consequently, these species have the highest values in terms of basal area, namely 25.29 respectively; 13.47 and 5.91 m² / ha. Considering diameter classes, values obtained showed that the maximum carbon storage (113.48t C/ha) is found within the class [20-30[. The minimum carbon storage (26.11t C/ha) is found in the class [1-10[.This is the class of small diameter trees, but the most dense (1461 ind / ha).Based on the results recorded in the plots, the maximum carbon stock was obtained in plot P12 (152.45 t C / ha). It is followed P3 and P9 with the values of 67.80 and 55.89 t C / ha respectively. The minimum carbon stock is in plot P14 (0.56 t C / ha). Thus, P12, P9 and P3 are the most productive plots. In addition, survey results show that fishing is the main activity carried out by the population living in the Rio del Rey estuary zone. Agriculture and wood exploitation are properly regulated. The subsistence fishing is considered as a lucrative activity, which procures subsistence products, provides various immediate benefits, and contributes to employment creation. Regarding the production of wood for smoking, it presents an essential part of tree felling. It should be noted that, the communities freely use these resources for daily needs without considering sustainable exploitation techniques. The current impact of these activities on mangroves remains low and could only be visible on a long-term basis.