Optimizing seeding density of fast-growing native trees for restoring the Brazilian Atlantic Forest

Direct seeding is a promising method for reducing restoration costs, but methodological adjustments are still needed to reduce the uncertainties to achieve a desired seedling density in the field. Here, we investigated the technical approaches and outcomes of direct seeding of fast-growing native trees for cost-effective restoration of the Brazilian Atlantic Forest. Sixteen tree species were manually sown at three seeding densities in planting lines prepared with a subsoiler, in two experimental areas, which were weeded with hoes and had leaf-cutter ants controlled with insecticide baits. Seedling density was monitored for 30, 90, and 180 days after sowing. No substantial change in tree density was observed 30 days after sowing, thus allowing fast corrective actions to adjust tree density. Only a minor proportion of the sown viable seeds resulted in established seedlings at 180 days (4-12% for the community; approximately 25% for the species with the best performance). However, tree density was high (6,000 on average; approximately 1,400-13,000 trees/ha) and allowed an effective canopy development. Overall, seedling density was linearly and positively associated with seeding density, was highly influenced by the species used, and was higher in the soil with higher sum of bases. Buying seeds would be, for most species, less costly than buying nursery-grown seedlings for achieving the expected tree densities in the field. These results evidence the potential of direct seeding for reducing restoration costs, as well as the need to select species with better performance and adjust seeding densities to optimize the use of this method.