Pression démographique et dynamique régressive du couvert végétal le long de la pénétrante nord de la ville de Yaoundé

Abstract

Demographic expansion is no longer viewed merely as an indicator of development; it now stands as one of the key driving forces behind the transformation of vegetation cover, particularly in African urban and peri-urban areas. In this context, the population along the northern corridor of Yaoundé, particularly in the neighborhoods of Nyom, Olembé, Emana, and Messassi, continues to increase, demanding more resources and living space, which places growing pressure on vegetation cover. The main objective of this thesis is to demonstrate the effects of this demographic pressure on the dynamics of vegetation cover along the northern corridor of Yaoundé. To achieve this objective, we formulated the general hypothesis that demographic pressure leads to the degradation of vegetation cover along the northern corridor of the city of Yaoundé. The methodology adopted relies on the collection of qualitative and quantitative data, including documentary research, semi-structured interviews, surveys with 263 households, floristic surveys on plots of 400 square meters each (20 m on each side), as well as the use of remote sensing and geographic information systems to evaluate the dynamics of vegetation cover between 1987 and 2022. The results reveal that the northern corridor of the city of Yaoundé has a heterogeneous, continuously growing population that is young and predominantly male. Human activities in the primary sector, such as agriculture and logging; in the secondary sector, such as quarrying; and in the tertiary sector, such as trade and the development of basic social services, have contributed to the dynamics of vegetation cover, leading to its degradation. The diachronic analysis of land use maps from 1987 to 2022 shows a significant decline in forest areas. In 1987, the forest covered 1,412.56 hectares, or 70% of the area. This percentage dropped to 55% in 2000, with 1,108.58 hectares, and then to just 24% in 2022, or 487.94 hectares. Meanwhile, the area occupied by housing has seen exponential growth, increasing from 376.17 hectares (18%) in 1987 to 638.42 hectares (31%) in 2000, reaching 1,152.73 hectares (57%) in 2022. Furthermore, the floristic surveys reveal a loss of floral diversity, with 49 individuals belonging to 20 families, 24 genera, and 29 species recorded in a forest plot, compared to 7 individuals distributed among 4 families, 5 species, and 4 genera in a plot located on the edge of a field. Invasive species, such as Chromolaena odorata and Pennisetum purpureum, have emerged. Moreover, demographic pressure has led to a decline in agricultural production along the northern corridor of Yaoundé. The perspectives highlight those future decisions related to the use and management of vegetation cover, as proposed, require strengthening the population's capacity for education, awareness, and action in the face of environmental challenges.