Biodiversity field trials to inform reforestation and natural resource management strategies along the African Great Green Wall in Senegal

Forest restoration is carried out with varying objectives in mind, one of which is biodiversity conservation. The present study examines the extent by which tree biodiversity could potentially be maximized in the context of the pan-African Great Green Wall for the Sahara and the Sahel Initiative (GGW). Towards this end, ten indigenous tree species were selected for study in the Ferlo region in Northern Senegal based on previous ethnobotanical studies in the zone. The species included Acacia senegal, Acacia nilotica, Acacia tortilis subsp. raddiana, Acacia seyal, Adansonia digitata, Balanites aegyptiaca, Dalbergia melanoxylon, Sclerocarya birrea, Tamarindus indica and Ziziphus mauritiana. Germination experiments were first performed in the laboratory on seed lots from Senegal, Burkina Faso, Kenya, and South Africa prior to in situ sapling production in the nursery in Northern Senegal situated along the GGW. A split plot field design was employed and the effects of seed provenance (two per species) and the addition of organic fertilizer at the timing of planting were determined. Over the course of the 2 year experimental period, the newly planted trees, in addition to the naturally regenerating woody vegetation and herbaceous grasses were monitored in the fenced-in experimental field plot. Of the ten species, only B. aegyptiaca, A. tortilis subsp. raddiana, and S. birrea exhibited moderate survival rates. The effects of provenance and fertilizer addition were sporadic and species-dependent. Natural regeneration of woody species was abundant albeit characterized by low biodiversity whereas herbaceous grass species showed extensive biodiversity, especially under tree canopies as compared to open areas.