Lessons on direct seeding to restore Neotropical savanna

Abstract

Tropical grassland-savanna mosaics are threatened globally, but they are challenging to restore because highly competitive pasture grasses inhibit recovery and are not shaded out by the patchy tree cover. We analyzed the outcomes of restoration projects and experiments established over four years in 55 ha of abandoned pastures dominated by invasive C4 grasses within the Neotropical savanna, Central Brazil. We tested the efficacy of direct seeding native grasses, forbs, shrubs and trees in reducing invasive grass cover and increasing native ground cover. We performed a series of experiments aimed at answering questions about the effect of seeding density, soil plowing to control invasive grasses, life form of ground cover species (grass, forb or shrub) and soil type on restoration outcomes. Relative native cover reached 34 ± 3% three rainy seasons after the first seeding experiment. Higher seeding densities and more soil plowing repetitions increased relative native cover. Soil type interacted with the life form of ground cover species to strongly influence relative native cover; two years after seeding, the highest relative native cover was achieved in rocky soils seeded with grasses (78 ± 6%) and the lowest was for seasonally waterlogged soils seeded with shrubs (15 ± 4%). Direct seeding can effectively establish many native Neotropical savanna species of different life forms with better restoration outcomes on rocky soils and with higher seeding densities. Further research is urgent to improve restoration methods, especially to control invasive grasses, to be able to achieve the large-scale restoration targets set internationally.