Abstract
In a widespread situation of climate change and biodiversity erosion, the sustainable management of territories and natural resources has become a central question in the development policies of countries. In Gabon, on the one hand, Libreville has developed into the main urban centre, rapidly concentrating a high demographic density compared with the rest of the country since the country first gained independence in the early 1960s. In addition, like the rest of the country, Gabon's capital is home to ecosystems that are rich in biodiversity and of major ecological importance (terrestrial forests and mangroves), which play an important role at local, regional and even international scale (sequestration of atmospheric carbon). The main aim of this thesis is therefore to study the impact of land artificialisation on Libreville's natural carbon sinks over a two-decade period from 2001 to 2022. Methods for the physical valuation of natural resources are built on the principle of strong sustainability, i.e. the maintenance of natural capital, and help to meet the requirements of sustainable development, in that they give natural capital an intrinsic value that has no equivalent in other types of capital, and therefore prevent any degradation of nature aiming to be compensated for by financial means. Ecosystem-based natural capital accounting, as used in the present study, allows natural resources to be physically assessed by means of accounting tables analysing their stocks, flows and state of health over a given period. The issue raised here is the difficulty of implementing such an approach on a sub-national scale and in an economically and socially disadvantaged region. To address these issues, it was decided to use mainly satellite remote sensing data from the Landsat series. Initially, the land cover maps produced using supervised classification of satellite images showed a predominance of dense forest in Libreville, with 274,738 ha in 2001, corresponding to 63% of terrestrial ecosystems, and 245,478 ha in 2022, corresponding to 57%. A shrinking forest cover has been observed over the years, and the nature of the changes observed has been determined through a diachronic analysis of land cover maps (2001-2014 and 2014-2022). Secondly, land cover and its dynamics were used as a proxy to analyse natural capital in physical terms, specifically vegetation biomass stocks and their changes. The total stock of carbon contained in biomass followed the same regressive trend as forests, falling from 160,411,151 tonnes to 154,921,690 tonnes between 2001 and 2022, a total loss of 5,489,461 tonnes. Finally, this work also looked at the efficiency of the public authorities' nature conservation actions, as reflected through the Arc d'Emeraude protected areas, despite the increasing land artificialisation in the Libreville region.