Humid forest on ultramafic substrates is globally rare, highly distinctive, and potentially highly vulnerable to disturbance, yet integrated ecological baselines for such systems are scarce. We combined pre-mining floristic inventories and woody transect data, plot-based structural baselines, soil chemistry comparisons, and regeneration data on seed rain and soil seed reserves to characterize humid ultramafic forest in the Ambatovy landscape of eastern Madagascar. The baseline recorded 426 woody species in 171 genera and 61 families across the humid ultramafic forest formations. Regeneration was strongly dependent on intact canopy: seed rain within forest averaged about 100 seeds m-2 yr-1 but was effectively absent in cleared areas, while the germinable soil seed reserve was shallow (about 19 seeds m-2) and dominated by pioneer taxa, with no mature-phase forest species detected. Post-mining waste-dump substrates were more limiting than intact forest soils, showing reduced carbon, nitrogen, potassium, organic matter, and permeability, together with elevated aluminium. These findings indicate that passive recovery of humid ultramafic forest after canopy removal is highly unlikely without intervention. We use these combined baselines to clarify the ecological rationale for active restoration, seed-source monitoring, nursery production, and ex situ conservation measures in one of the world's few humid ultramafic rainforest systems.