Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Long-term dynamics (1961-2021) of the woody vegetation in the savannas of the Senegalese silvopastoral region : an approach combining inventories time series, historical database and very high-resolution imagery

Auteur : Dewaersegger, Manoël

Université de soutenance : Université catholique de Louvain

Grade : Master : bioingénieur en gestion des forêts et des espaces naturels, à finalité spécialisée 2022

Résumé
The Sahelian silvopastoral system strongly relies on the woody vegetation of its savanna ecosystems. This resource has been threatened by the Great Drought of the 1970s and 1980s that led to a loss of woody cover and species richness. We combined inventories time series, an historical inventories database and very high-resolution imagery to investigate the temporal trends of woody vegetation from 1961 to 2021 at the level of the Senegalese silvopastoral region, encompassing the Sandy and the Lateritic ecoregions. From 1989 to 2021, no trends were detected in botanical composition, species richness and density, while woody cover increased in the Southern part of the study area. Extending the study period to 1961, successive shifts of botanical composition were observed in the Sandy ecoregion, while the Lateritic ecoregion showed a stable trend of species composition change. These findings highlight the importance of soil type on vegetation dynamics and suggest that recent disturbances are acting on the Sahelian ecosystems of Senegal. Because of the altered disturbance regimes caused by climate change, robust monitoring programs will be required to enforce adaptative management in these ecosystems. The inventories time series are crucial to study vegetation dynamics, while very high-resolution imagery is a promising complementary tool. The time series provided by the Sentinel satellites could be integrated to initiate a continuous monitoring program of the woody vegetation, that will be crucial for the future management of this precious natural resource.

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