Methodological integration for enhanced analysis of the structure of forest patches in Western Africa
BORIS DOI
Abstract
Tropical forests are increasingly threatened by deforestation, fragmentation, and degradation, primarily driven by agriculture, logging, and fire. In Western Africa, thousands of small and isolated forest patches persist in agriculture-dominated landscapes. Although often unprotected, these forests provide essential ecosystem services such as biodiversity conservation, carbon storage, and the supply of resources like timber and bushmeat, while also holding cultural and spiritual significance. Safeguarding them requires a deeper understanding of their ecological functioning, as well as innovative monitoring approaches and consideration of local socio-economic realities.
However, knowledge about the structure of these forests—an essential ecological feature—is limited. Forest structure determines whether a forest is composed of large versus small trees, how canopy layers are organized, and whether gaps dominate the canopy. Such attributes are directly linked to forest biomass and carbon sequestration, both of which are key indicators of ecological functioning. This thesis contributes to closing this knowledge gap by analyzing the structure, aboveground biomass (AGB), and tree species richness of tropical forest patches across Western Africa. The research focused on nine forest patches in Togo, Benin, Nigeria, and Cameroon, based on 121 forest plots with tree inventories and species identifications.
The results revealed relatively intact forest structure and high aboveground biomass (85–260 Mg/ha), as well as the presence of several vulnerable and endangered tree species such as Afzelia bipindensis and Guibourtia tessmannii. At the same time, the forest patches showed pronounced edge effects: degradation was most visible near the edges, while more intact zones were confined to the core. Structural metrics—including basal area, canopy height, species richness, complexity, and tree vitality—increased with distance from the edge. In highly isolated patches, edge effects also reduced AGB and wood density. AGB values in the studied community forests were lower than those in nearby officially protected areas, underscoring the importance of conservation measures beyond formal reserves.
Beyond describing ecological conditions, this thesis advances methodological innovation for forest assessment. A terrestrial laser scanner (TLS) was tested to estimate AGB and compared with manual inventories. While both methods produced moderately correlating results, challenges remained due to sensor occlusion and the lack of species-specific wood density data. In addition, unmanned aerial vehicles (UAVs) equipped with LiDAR and multispectral sensors enabled fine-scale disturbance mapping, complementing ground-based information on forest structure and vitality. Together, these tools demonstrate how emerging technologies can improve monitoring of fragmented tropical forests.
Finally, the thesis integrates social dimensions to contextualize ecological findings. Through 328 interviews with regular forest users, it examined local perceptions of forest integrity and forest-related activities such as hunting and logging. Results revealed contrasting perspectives: in intensively used areas, degradation was often not perceived as a major concern, whereas communities maintaining sacred forests showed strong awareness of threats such as fire and illegal logging. Forests near urban centers exhibited higher exploitation pressure, and interviewees frequently reported declining forest areas and the disappearance of key species. These insights highlight the role of cultural traditions and socio-economic contexts in shaping both forest condition and conservation prospects.
Taken together, the results highlight that Western Africa’s remaining forest patches retain important ecological value—relatively intact structures, high biomass stocks, and threatened species—yet remain highly vulnerable to edge effects and human pressure. To safeguard their ecological and social value, this thesis recommends conservation strategies such as establishing buffer zones to reduce edge degradation, reconnecting fragments with habitat corridors, and integrating socio-economic approaches into forest management. By combining ecological analysis, methodological innovation, and social perspectives, the thesis advances knowledge on tropical forest functioning and provides tools and strategies for their sustainable management.
However, knowledge about the structure of these forests—an essential ecological feature—is limited. Forest structure determines whether a forest is composed of large versus small trees, how canopy layers are organized, and whether gaps dominate the canopy. Such attributes are directly linked to forest biomass and carbon sequestration, both of which are key indicators of ecological functioning. This thesis contributes to closing this knowledge gap by analyzing the structure, aboveground biomass (AGB), and tree species richness of tropical forest patches across Western Africa. The research focused on nine forest patches in Togo, Benin, Nigeria, and Cameroon, based on 121 forest plots with tree inventories and species identifications.
The results revealed relatively intact forest structure and high aboveground biomass (85–260 Mg/ha), as well as the presence of several vulnerable and endangered tree species such as Afzelia bipindensis and Guibourtia tessmannii. At the same time, the forest patches showed pronounced edge effects: degradation was most visible near the edges, while more intact zones were confined to the core. Structural metrics—including basal area, canopy height, species richness, complexity, and tree vitality—increased with distance from the edge. In highly isolated patches, edge effects also reduced AGB and wood density. AGB values in the studied community forests were lower than those in nearby officially protected areas, underscoring the importance of conservation measures beyond formal reserves.
Beyond describing ecological conditions, this thesis advances methodological innovation for forest assessment. A terrestrial laser scanner (TLS) was tested to estimate AGB and compared with manual inventories. While both methods produced moderately correlating results, challenges remained due to sensor occlusion and the lack of species-specific wood density data. In addition, unmanned aerial vehicles (UAVs) equipped with LiDAR and multispectral sensors enabled fine-scale disturbance mapping, complementing ground-based information on forest structure and vitality. Together, these tools demonstrate how emerging technologies can improve monitoring of fragmented tropical forests.
Finally, the thesis integrates social dimensions to contextualize ecological findings. Through 328 interviews with regular forest users, it examined local perceptions of forest integrity and forest-related activities such as hunting and logging. Results revealed contrasting perspectives: in intensively used areas, degradation was often not perceived as a major concern, whereas communities maintaining sacred forests showed strong awareness of threats such as fire and illegal logging. Forests near urban centers exhibited higher exploitation pressure, and interviewees frequently reported declining forest areas and the disappearance of key species. These insights highlight the role of cultural traditions and socio-economic contexts in shaping both forest condition and conservation prospects.
Taken together, the results highlight that Western Africa’s remaining forest patches retain important ecological value—relatively intact structures, high biomass stocks, and threatened species—yet remain highly vulnerable to edge effects and human pressure. To safeguard their ecological and social value, this thesis recommends conservation strategies such as establishing buffer zones to reduce edge degradation, reconnecting fragments with habitat corridors, and integrating socio-economic approaches into forest management. By combining ecological analysis, methodological innovation, and social perspectives, the thesis advances knowledge on tropical forest functioning and provides tools and strategies for their sustainable management.
Date of Publication
2025
Year of graduation
2025
Theses Type
dissertation
Subject(s)
Language(s)
en
Author(s)
Faculty/Graduate School
Institute
Access(Rights)
open.access
Primary OA Publication
true