Legacy of Amazonian Dark Earth soils on forest structure and species composition

Aim: Amazonian forests predominantly grow on highly weathered and nutrient
poor soils. Anthropogenically enriched Amazonian Dark Earths (ADE),
traditionally known as Terra Preta de Índio), were formed by pre-Columbian
populations. ADE soils are characterized by increased fertility and have
continued to be exploited following European colonization. Here, we
evaluated the legacy of land-use and soil enrichment on the composition
and structure in ADE and NDE forests. Location: Eeastern and southern
Amazonia Time period: Pre-Columbia - 2014 Methods: We sampled nine pairs
of ADE and adjacent NDE forest plots in eastern and southern Amazonia. We
collected soil samples per plot at 0-10 and 10-20 cm depth and measured
stem diameter, height, and identified all individual woody plants (palms,
trees, and lianas) with diameter ≥10 cm. We compared soil physicochemical
properties, vegetation diversity, floristic composition, aboveground
biomass, and percentage of useful species. Results: In the nine paired
plots, soil fertility was significantly higher in ADE soil. We sampled
4191 individual woody plants representing 404 species and 65 families. The
floristic composition of ADE and NDE forests differed significantly at
both local and regional levels. In southern Amazonia, ADE forests had, on
average, higher aboveground biomass than other forests of the region,
while in eastern Amazonia, biomass was similar to that of NDE forests.
Species richness of both forest types did not differ and was within the
range of existing regional studies. The differences in composition between
trees of large and small diameter recruits may indicate long-term recovery
and residual effects from historical land-use. Additionally, the
proportion of edible species tended to be higher in the ADE forests of
eastern and southern Amazonia. Main conclusions: The marked differences in
soil fertility, floristic composition and aboveground biomass between ADE
and NDE forests are consistent with a small-scale long-term land-use
legacy.