Impact of anthropogenic activities on the vegetation structure of mangrove forests in Kribi, the Nyong river mouth and Cameroon estuary

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

appears important.