RESUMO
Indigenous societies are known to have occupied the Amazon basin for more than 12,000 years, but the scale of their influence on Amazonian forests remains uncertain. We report the discovery, using LIDAR (light detection and ranging) information from across the basin, of 24 previously undetected pre-Columbian earthworks beneath the forest canopy. Modeled distribution and abundance of large-scale archaeological sites across Amazonia suggest that between 10,272 and 23,648 sites remain to be discovered and that most will be found in the southwest. We also identified 53 domesticated tree species significantly associated with earthwork occurrence probability, likely suggesting past management practices. Closed-canopy forests across Amazonia are likely to contain thousands of undiscovered archaeological sites around which pre-Columbian societies actively modified forests, a discovery that opens opportunities for better understanding the magnitude of ancient human influence on Amazonia and its current state.
Assuntos
Arqueologia , Florestas , Humanos , BrasilRESUMO
Smallholder agriculture is the main driver of deforestation in the western Amazon, where terrestrial biodiversity reaches its global maximum. Understanding the biodiversity value of the resulting mosaics of cultivated and secondary forest is therefore crucial for conservation planning. However, Amazonian communities are organized across multiple forest types that support distinct species assemblages, and little is known about smallholder impacts across the range of forest types that are essential for sustaining biodiversity. We addressed this issue with a large-scale field inventory of birds (point counts) and trees (transects) in primary forest and smallholder agriculture in northern Peru across 3 forest types that are key for Amazonian biodiversity. For birds smallholder agriculture supported species richness comparable to primary forest within each forest type, but biotic homogenization across forest types resulted in substantial losses of biodiversity overall. These overall losses are invisible to studies that focus solely on upland (terra firma) forest. For trees biodiversity losses in upland forests dominated the signal across all habitats combined and homogenization across habitats did not exacerbate biodiversity loss. Proximity to forest strongly predicted the persistence of forest-associated bird and tree species in the smallholder mosaic, and because intact forest is ubiquitous in our study area, our results probably represent a best-case scenario for biodiversity in Amazonian agriculture. Land-use planning inside and outside protected areas should recognize that tropical smallholder agriculture has pervasive biodiversity impacts that are not apparent in typical studies that cover a single forest type. The full range of forest types must be surveyed to accurately assess biodiversity losses, and primary forests must be protected to prevent landscape-scale biodiversity loss.
Pérdida de Biodiversidad Pasada por Alto en la Agricultura de Pequeños Propietarios Resumen La agricultura de pequeños propietarios es la principal causa de la deforestación en la Amazonía occidental, donde la biodiversidad terrestre alcanza su máximo global. Por lo tanto, comprender el valor de la biodiversidad de los mosaicos resultantes de bosques cultivados y secundarios es crucial para para la planificación de la conservación. Sin embargo, las comunidades amazónicas están organizadas a través de múltiples tipos de bosques que soportan ensambles de especies distintas, y poco se sabe sobre los impactos de los pequeños agricultores en toda la gama de tipos de bosques que son esenciales para mantener la biodiversidad. Abordamos este problema con un inventario de campo a gran escala de aves (puntos de conteo) y árboles (transectos) en bosques primarios y agricultura de pequeños productores en el norte de Perú en 3 tipos de bosques que son clave para la biodiversidad amazónica. Para aves, la agricultura de pequeños productores soportó una riqueza de especies comparable a la de los bosques primarios dentro de cada tipo de bosque, pero la homogeneización biótica entre los tipos de bosques dio lugar a pérdidas sustanciales de biodiversidad en general. Estas pérdidas globales son invisibles para los estudios que se centran únicamente en los bosques de tierra firme. En el caso de árboles, las pérdidas de biodiversidad en bosques de tierra firme fueron dominantes en todos los hábitats combinados y la homogeneización en todos los hábitats no agravó la pérdida de biodiversidad. La proximidad a los bosques predijo robustamente la persistencia de especies de aves y árboles asociadas a bosques en el mosaico de pequeños productores, y debido a la omnipresencia de bosque intacto en el área de estudio, nuestros resultados probablemente representan el mejor escenario para la biodiversidad en la agricultura amazónica. La planificación del uso de suelo dentro y fuera de las áreas protegidas debe reconocer que la agricultura tiene impactos generalizados sobre la biodiversidad que no son evidentes en estudios que solo abarcan un solo tipo de bosque. Se debe examinar toda la gama de tipos de bosque para evaluar con precisión las pérdidas de biodiversidad, y los bosques primarios deben ser protegidos para prevenir la pérdida de biodiversidad a escala de paisaje.
Assuntos
Biodiversidade , Conservação dos Recursos Naturais , Agricultura , Animais , Florestas , Peru , ÁrvoresRESUMO
The forests of western Amazonia are among the most diverse tree communities on Earth, yet this exceptional diversity is distributed highly unevenly within and among communities. In particular, a small number of dominant species account for the majority of individuals, whereas the large majority of species are locally and regionally extremely scarce. By definition, dominant species contribute little to local species richness (alpha diversity), yet the importance of dominant species in structuring patterns of spatial floristic turnover (beta diversity) has not been investigated. Here, using a network of 207 forest inventory plots, we explore the role of dominant species in determining regional patterns of beta diversity (community-level floristic turnover and distance-decay relationships) across a range of habitat types in northern lowland Peru. Of the 2,031 recorded species in our data set, only 99 of them accounted for 50% of individuals. Using these 99 species, it was possible to reconstruct the overall features of regional beta diversity patterns, including the location and dispersion of habitat types in multivariate space, and distance-decay relationships. In fact, our analysis demonstrated that regional patterns of beta diversity were better maintained by the 99 dominant species than by the 1,932 others, whether quantified using species-abundance data or species presence-absence data. Our results reveal that dominant species are normally common only in a single forest type. Therefore, dominant species play a key role in structuring western Amazonian tree communities, which in turn has important implications, both practically for designing effective protected areas, and more generally for understanding the determinants of beta diversity patterns.