Search

The Great Green Wall (GGW) is an international initiative to combat land degradation and restore native plant life in the Sahel, but due to a lack of monitoring tools, it remains unknown to be considered as success or failure. Here, we quantify the impact of GGW plantations and Corporate plantations (privately owned) in Sahelian Senegal based on remote sensing data and deep learning by mapping individual trees and their biomass across the Sahel region. Tree features (cover, density and above-ground biomass) have been computed in every hectare of 42 plantations (of both, corporate and GGW) and their surrounding non-planted areas, subsequently used for a comparative analysis of tree features. Results showed that gains in tree features varied substantially between plantations. At plot scale, among Corporate plantations, the average gain in tree density was 61.16±42.12 trees/ha while it was 5.7 ± 5.8 trees/ha for GGW plantations. In regards to tree cover, the average gain was 618.5 ± 588.5 m2/ha for Corporate plantations and 71.72±108.89 m2/ha for GGW plantations. For the above-ground biomass, the average gain was 3.36±3.29 tons/ha in the Corporate plantations and 0.46±0.67 tons/ha in the GGW plantations. The average gain in foliar biomass in the Corporate plantations was 0.15±0.13 tons/ha and in the GGW plantations, it was 0.02±0.03 tons/ha. The average gain in wood biomass was 3.21±3.12 tons/ha among the Corporate plantations and was 0.43±0.64 tons/ha among the GGW plantations. Notably, regarding the relative benefit in terms of ecosystem services per unit of density, each tree in GGW plantations contribute more to ecosystem services per unit of density compared to Corporate plantations. In GGW, each gained tree contributes 18 m2 of cover, 116.1 kg of above-ground biomass, 5.6 kg of foliar biomass, and 114.2 kg of woody biomass, while in corporate plantations, on the other hand, each gained tree adds 9 m2 of cover, 48.4 kg of above-ground biomass, 2.3 kg of foliar biomass, and 46.3 kg of woody biomass. These findings are opposed to conventional paradigms, suggesting that the Great Green Wall, while perhaps missing its tree density targets, has succeeded in its mission to produce ecosystem services per tree. This raises important questions about the redefinition of objectives in reforestation projects, focusing on quality rather than quantity, a perspective that could transform our understanding of the successes and failures of these essential ecological restoration initiatives. However, the assessment primarily relies on indicators such as cover and biomass, potentially overlooking other crucial ecosystem services. Therefore, while our conclusions underscore the effectiveness of reforestation initiatives, future research should aim to establish a more comprehensive understanding of ecosystem services by incorporating additional indicators beyond cover and biomass, such as species diversity, soil health, water retention, and habitat quality.

Since the 1960s, droughts have caused significant degradation of Sahelian ecosystems, particularly resulting in a reduction in tree cover. Despite the challenges posed by climate change, the rural Sahelian population continues to depend on natural resources for pastoral livestock farming, which remains a critical source of livelihood. To address this issue of land degradation, Sahelian states and international coalitions are prioritizing efforts to restore pastoral land through reforestation programs. These initiatives aim to enhance ecosystem services, generate new income for the population, and safeguard biodiversity.In practice, however, reforestation has often led to a depletion of resources for communities due to enclosure policies. This paper explores various land management models for reforestation within a pastoral context through provisioning ecosystem services (PES) modeling.This study quantifies the economic potential of PES offered by reforestation programs in Senegal. It employs a quantitative methodology to assess the profitability of these operations from the perspective of pastoral economies. The analysis reveals that the PES benefits of reforestation can significantly enhance the economic potential of sylvo-pastoral productions if resource access is negotiated collaboratively between pastoralists and forestry extension services during reforestation activities and after. From an investment perspective, the economic viability of reforestation operations in drylands is questionable. The findings suggest that when evaluated solely in terms of PES profitability, these programs may not be financially sustainable. The sustainability of these investments would require taking into account supporting and regulating ecosystem services.

Local knowledge on temporal indicators in the Guinean zone of Togo Description of the subject. Important changes in cropping seasons caused by a decrease and erratic patterns in rainfall have forced farmers to redefine their agricultural calendars, which are based on local knowledge. Objectives. The objective of this study was to promote local knowledge used in farming schedules. The specific objectives were to identify biophysical indicators used for planning cropping calendars, and to determine the target plant species common to all ecological zones. Method. In total, 689 farmers distributed through 65 localities were surveyed through semi-direct interviews and focus group discussions. Results. All respondent farmers reported relying on temporal markers for defining their cropping calendars, especially the recognition of the onset of the rainy season (sowing period) and rainfall cessation or the dry season (harvesting period). These biological indicators are mainly related to plant phenology, especially flowering (Triumfetta rhomboidea Jacq., Spathodea campanulata P.Beauv.) and fruiting (Vitellaria paradoxa C.F.Gaertn.), which are used to indicate the beginning of the dry season. The flowering of Millettia thonningii (Schum. & Thonn.) Baker, V. paradoxa, Delonix regia (Hook.) Raf. and the opening of ripened fruits (Ceiba pentandra [L.] Gaertn.) are used to identify the onset of the rainy season. A total of 67 species were identified as indicators of agricultural seasons. In addition to these plant species, the seasonal migration of birds (73%), and of insects (48%); and some abiotic indicators such as wind direction (100%), star observations (82%) and cloud movement (69%) were reportedly used as landmarks in farming time management. Conclusions. Knowledge about these signals is useful for anticipating possible climate variability based on traditional meteorological forecasting and for guiding local cropping calendars. This local knowledge regarding temporal markers is therefore relevant for agricultural adaptation to climate change.

The diversity and structure of plant communities are valuable indicators for assessing landscape quality. Land-use change is one of the main factors considered to affect and have the strongest impacts on biodiversity. In this study, we assessed the effects of the conversion of tropical dry forests and savannahs into agricultural lands on the floral diversity and the structure of the vegetation. For this purpose, we carried out vegetation surveys in 198 plots of 50 m × 50 m. Within each plot, we documented all herbaceous, shrubby, and tree species present. We calculated total, spatial, and local floral diversities by land-use types and characterized the structure of the plant communities. Our results show that the overall floral diversity of the study area remains quite high (483 species of vascular plants from 298 genera and 71 families) and was not strongly impacted by agricultural land use (Pareto inequality index is 23–77). Croplands had the highest spatial (9.4) and local diversities. There was no significant difference between the land-use types in terms of the native species richness while croplands harbored significantly the most alien species. Agricultural land use significantly affected the structure of the plant communities. Trees are very rare in croplands and are frequent in forests and savannahs. The clearing of Guinean dry forests and savannahs for cropping did not automatically lead to a loss of some aspects of ordinary floral diversity. For a better understanding of the effects of land-use change on biodiversity, it would then be more suitable to specify in the studies whether the species concerned are native, alien, generalist, or specialist.