Secondary forests on anthropogenic soils in Brazilian Amazonia conserve agrobiodiversity

Throughout Brazilian Amazonia anthropogenic soils that are the product of pre-Columbian settlements are called Terra Preta de Índio (Indian Dark Earths, TPI). These soils are dramatically different from surrounding soils due to long-term human activity, but there is little information about how secondary forest succession is affected by these differences. We tested if community structure (density, richness and basal area), floristic composition and domesticated species’ richness and density were similar between TPI and non-anthropogenic soils (NAS) in 52 25 × 10 m secondary forest plots in different successional stages near three traditional communities along the middle Madeira River, Central Amazonia. We sampled 858 woody individuals on TPI (77 domesticated) and 1095 on NAS (27 domesticated); 550 understory palms on TPI (169 domesticated) and 778 on NAS (123 domesticated). We found 179 species on TPI (10 domesticated), 190 on NAS (8 domesticated), and 74 (25%) in both environments. Although community structure on TPI and NAS was fairly similar, they showed significantly distinctive floristic compositions, both for woody individuals and understory palms. The density and richness of domesticated species was significantly higher on TPI than on NAS for woody individuals, but not for palms. The intimate long-term association of TPI with human activity has lead to the formation of distinct secondary forests and has favored the concentration of domesticated populations of crop species. Hence, secondary forests on anthropogenic soils concentrate agrobiodiversity, offering advantages for in situ conservation of genetic resources, and are unique ecosystems that should be considered in conservation efforts.