Farmer Managed Natural Regeneration Promotes Expansion of Trees on Croplands in the Sahel

<title>Abstract</title> The expansion of trees on croplands in the Sahel has been promoted as a nature-based solution to climate challenges, particularly through Farmer Managed Natural Regeneration (FMNR). Yet large-scale assessments of cropland tree dynamics remain scarce. Here, we combine 25 years of Landsat imagery with a deep learning model trained on 9.9 billion trees to reconstruct annual tree cover at 15 m resolution across 2.4 million km² of Sahelian croplands. We find that 12% of all Sahelian trees occur on croplands and that 9.2 million hectares have gained tree cover since 1999. Gains are concentrated near villages and in regions with longstanding FMNR promotion, especially Maradi and Zinder. Areas with moderate to high FMNR intensity show greater increases than low-intensity areas. These findings provide large-scale evidence that farmer-led management has driven cropland greening, offering insights for sustainable land management, and establishing a framework for monitoring scattered trees in drylands.