Dynamiques de la diversité ligneuse et des stocks de carbone dans les forêts denses semi-décidues de production du Cameroun : cas de la forêt communale de Dimako.

Abstract

The interest shown by the Cameroonian government for an ecologically acceptable, economically viable and socially equitable management of communal forests continues to grow due to the increasing threats to its plant potential and carbon stocks. Thanks to measures aimed at reducing the impact of logging, it is possible to envisage the conservation and/or restoration of biodiversity. The objective of this study was to highlight the evolution of plant diversity and carbon stocks in the aftermath of industrial logging in the Annual Allowable Cut (AAC) of different ages in the Dimako Communal Forest (DCF). This with a view to providing decisionmakers with basic tools that can contribute to the sustainable management of natural resources, by providing answers to the questions of the implementation of REDD + in production forests in Cameroon. The present study was carried out in a diachronic and synchronic mode. Field data were collected in January 2020. The dynamics of land occupation within the DCF were established from the satellite images of the sensors of the series Landsat Enhanced Thematic Mapper (ETM) (1984), ETM (2000) and Sentinel 2A of 2015. The latter is considered as reference years. To characterize the ligneous plants, a sampling plan was made up of 0.5 ha (250 m × 20 m) plots, subdivided into ten sub-plots of 25 m × 20 m for the inventory of all trees of diameter at breast height (dbh at 1.30 m height of tree) greater than or equal to 10 cm. Three 10 m × 10 m quadrats were installed at the start (0 m), in the middle (125 m) and at the end (250 m) of each plot for inventories of individuals of dbh between 5 and 10 cm. Within each 10m x 10m quadrat, a 5m x 5m sub-quadrat was installed for counting of 1 cm  dbh  5 cm stems. The results obtained made it possible to identify five land use units in 1984 and 2000 and six land use units in 2015. Woody formations represent the most dominant land use categories. Forest cover declined at a rate of -94.07 ha / year between 1984 and 2000; on the other hand, following the actions of the municipality such as reforestation, an increase of the order of 100.59 ha / year was observed between 2000 and 2015. It emerges from this study that logging causes changes in the vertical and horizontal structures of the forest landscape. The evolution of the different harvestable areas reveals a reduction of 30.45% of woody species, of 20% of genera and of 14.28% of families between the Annual Allowable Cut (AAC6-3) not exploited and the AAC3 -5. Between the control harvestable area and the AAC2-5 the regression is 15.15% of woody species, 7.62% of genera and 12.94% of families. These values are 1.78%, 5.26 and -7.69% respectively for woody species, genera and families between the control harvestable area and AAC1-5. For the species inventoried within the framework of this study, three categories of threatened species were observed in the controlharvestable area (CR, VU and NT), two categories in AAC1-5, in AAC2-5 and in AAC3-5 (VU and NT). The evolution of carbon stocks varies from one pool to another. The decline in aerial carbon stocks is more pronounced in AAC1-5 (19.10%) followed by AAC3-5 (10.27%) and finally in AAC2-5 (9.04%). Intact carbon stocks are similar in AAC2-5 and AAC3-5 and low in AAC1-5. Analyses show that carbon stocks increase over time. The modelling of the dynamics of the exploitable stock in the logged annual allowable cut areas shows that forests logged under a management plan requires up to 167.24 years to recover whereas the rotation is limited to 30 years. The modelling proposed in production forests shows that sustainable management would only marginally limit the damage caused by logging. In view of the various analyses carried out as part of this study, it is not superfluous to underline the importance of forest management in maintaining and restoring plant cover and by extension the conservation of biodiversity.