Direct seeded and colonizing species guarantee successful early restoration of South Amazon forests

Abstract

South Amazon forests have been highly deforested, including the legally protected riparian forests. The Xingu watershed restoration program used direct seeding of native trees to restore 5000 ha of forests from 2006 to 2018. Direct seeding is a low cost method, easy-to-implement at large scales. The literature on this method concludes that only a few species manage to establish successfully, resulting in an impoverished forest. In this study, we aimed to (i) assess changes in species composition over a 10-year chronosequence in direct seeded sites, (ii) evaluate life-history traits of direct seeded and colonizer species, and (iii) investigate whether colonizer arrival is influenced by landscape structure and dispersal syndrome. We sampled 72 1–10 year-old direct seeded sites along a latitudinal gradient of 600 km, at the Upper Xingu Basin, state of Mato Grosso, Brazil. From the 152 direct seeded species, 90 species established themselves, and 67 new species colonized the restored sites. Succession started off dominated by a single pioneer species; then shared dominance with five other light-demanding species, while slow-growing species were present in the understory. Direct seeded and established species are disproportionately more orthodox, wind-dispersed seeds, usually dispersing during the dry season. Colonizer species are similar to the ones found in reference forests, regarding the proportion of animal-dispersed and recalcitrant seeds. We found no relationship between forest cover and colonizer richness. Direct seeding imposes a functional diversity filter due to the short period of seed harvesting, storage limitations, and field emergence. However, established species comprise diverse successional classes, which form an initial structure that facilitates species colonization, reducing the biodiversity filters caused by the direct seeding method over the years.