More than 10,000 pre-Columbian earthworks are still hidden throughout Amazonia.

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.

Environmental drivers of forest structure and stem turnover across Venezuelan tropical forests.

Using data from 50 long-term permanent plots from across Venezuelan forests in northern South America, we explored large-scale patterns of stem turnover, aboveground biomass (AGB) and woody productivity (AGWP), and the relationships between them and with potential climatic drivers. We used principal component analysis coupled with generalized least squares models to analyze the relationship between climate, forest structure and stem dynamics. Two major axes associated with orthogonal temperature and moisture gradients effectively described more than 90% of the environmental variability in the dataset. Average turnover was 1.91 ± 0.10% year-1 with mortality and recruitment being almost identical, and close to average rates for other mature tropical forests. Turnover rates were significantly different among regions (p < 0.001), with the lowland forests in Western alluvial plains being the most dynamic, and Guiana Shield forests showing the lowest turnover rates. We found a weak positive relationship between AGB and AGWP, with Guiana Shield forests having the highest values for both variables (204.8 ± 14.3 Mg C ha-1 and 3.27 ± 0.27 Mg C ha-1 year-1 respectively), but AGB was much more strongly and negatively related to stem turnover. Our data suggest that moisture is a key driver of turnover, with longer dry seasons favoring greater rates of tree turnover and thus lower biomass, having important implications in the context of climate change, given the increases in drought frequency in many tropical forests. Regional variation in AGWP among Venezuelan forests strongly reflects the effects of climate, with greatest woody productivity where both precipitation and temperatures are high. Overall, forests in wet, low elevation sites and with slow turnover stored the greatest amounts of biomass. Although faster stand dynamics are closely associated with lower carbon storage, stem-level turnover rates and woody productivity did not show any correlation, indicating that stem dynamics and carbon dynamics are largely decoupled from one another.

Hyperdominance in Amazonian forest carbon cycling.

While Amazonian forests are extraordinarily diverse, the abundance of trees is skewed strongly towards relatively few 'hyperdominant' species. In addition to their diversity, Amazonian trees are a key component of the global carbon cycle, assimilating and storing more carbon than any other ecosystem on Earth. Here we ask, using a unique data set of 530 forest plots, if the functions of storing and producing woody carbon are concentrated in a small number of tree species, whether the most abundant species also dominate carbon cycling, and whether dominant species are characterized by specific functional traits. We find that dominance of forest function is even more concentrated in a few species than is dominance of tree abundance, with only ≈1% of Amazon tree species responsible for 50% of carbon storage and productivity. Although those species that contribute most to biomass and productivity are often abundant, species maximum size is also influential, while the identity and ranking of dominant species varies by function and by region.

Simulación de la dinámica de un bosque tropical en los llanos occidentales de Venezuela / Simulation of a tropical forest in the western plains of Venezuela

Los datos de parcelas permanentes, establecidas en un bosque estacional de los llanos occidentales venezolanos, se usaron para establecer los parámetros de FACET, un modelo basado en árboles individuales y sensible a las características topográficas del terreno. Debido a su alto número, las especies arbóreas se agruparon de acuerdo con su tolerancia a la sombra (tolerantes, intermedias e intolerantes) y su altura máxima (grandes, medianas y pequeñas). Las palmas fueron consideradas como un grupo separado. La dinámica forestal fue simulada para cada posición fisiográfica (banco, sub-banco y bajío). Los resultados de la simulación para un periodo de 210 años se aproximan a la dinámica esperada tanto para banco como sub-banco, no así para bajío. Tras una simulación de 500 años, en banco las tolerantes grandes dominan el área, acumulando un índice de valor (IV) de 27,28 seguidas por las palmas con un IV= 18,86; igual ocurre en sub-banco donde las tolerantes grandes predominan con un IV= 26,78 y las palmas acumulan 20,27; lo que se corresponde a la composición esperada para un bosque sin perturbaciones. En bajío, las tolerantes grandes también mantienen el primer lugar con un IV= 28,74 pero las siguen las intermedias grandes con 20,27. En conclusión, el modelo FACET tiene gran potencialidad para predecir la dinámica de bosques tropicales, excepto en las áreas de bajío con problemas de drenaje. En consecuencia, es necesario introducir modificaciones en la rutina de balance de agua en el suelo para lograr una mejor representación de la dinámica forestal en esos sitios