Historical landscape domestication in ancestral forests with nutrient-poor soils in northwestern Amazonia

Abstract

Past human modification of forests has been documented in central, southwestern, and eastern Amazonia, especially near large rivers. Northwestern Amazonia, and interfluvial forests there in particular, are assumed to exhibit little past human impact. We analyzed soils and floristic structure and composition of interfluvial forests located in the Içana River basin, northwestern Amazonia, to assess their degree of past human modification. Ancient Baniwa village sites, abandoned centuries ago, have given rise to “ancestral forests” with as much as 57% of all trees/palms belonging to a group of species managed currently by the Baniwa, compared to only 10% of such species in old-growth forests that are not remembered as having been inhabited or managed in Baniwa oral tradition. Participatory mapping and direct observations revealed ancestral forests to be widely distributed throughout the region, whereas old-growth forests are rare. Managed species in ancestral forests contributed 5-fold more to total tree/palm biomass than in old-growth forests. Human management has produced lasting changes in floristic composition, maintained total tree/palm biomass, and improved soil quality. This is the first study to demonstrate past human modification in Amazonian interfluvial forests, while explicitly isolating historical human management from edaphic effects on floristic structure and composition. Despite environmental limitations on human population size, posed by nutrient-poor black water rivers and acidic, sandy soils, indigenous peoples of northwestern Amazonia left a clear, lasting cultural legacy in ancestral forests. Given legal changes that threaten indigenous peoples' land rights currently under debate in Brazil, we call for a reconsideration of biodiversity conservation policies and indigenous rights in areas that show enduring legacies of management by indigenous populations.