Regeneration impoverishment of Sahelian woody communities put them at risk in three land management types

Abstract

Abstract Trees play a key role in drylands. Monitoring woody communities regeneration and understanding the drivers of its success is crucial to apprehend their long-term persistence. While fire, grazing and water availability are key factors for regeneration in drylands, seeds arrival, germination and seedlings recruitment are still poorly studied in natural conditions in the West African Sahel. To promote regeneration, tree planting is a common tool used in West Africa. The cost is great, the success variable and their influence on spontaneous regeneration is unknown. In this study, we conducted field inventory to characterize the regeneration ability of woody communities in a Sahelian savanna. We investigated regeneration and adults stands in three land management types (plantations, communal grazing, old enclosures) to determine (i) the proportion of the regeneration modes and the influence of mature trees; (ii) the influence of management type and topography on regeneration; and (iii) their temporal dynamics. We first showed that the regeneration diversity is poor, with half of the adult species not recorded in the regeneration phase. Most of the regeneration came from true seedlings compared to resprout. Second, mature trees have a strong influence on regeneration density and composition. Third, topography influences regeneration density whereas we observed little effect of the land management type. Finally, historical data highlighted a steep decline of regeneration density these last decades. These results question the persistence of woody vegetation in Sahelian savannas and highlight the need to protect large trees, in suitable micro-sites such as depressions to favor regeneration.