One sixth of Amazonian tree diversity is dependent on river floodplains.

Amazonia's floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region's floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon's tree diversity and its function.

Biased-corrected richness estimates for the Amazonian tree flora.

Amazonian forests are extraordinarily diverse, but the estimated species richness is very much debated. Here, we apply an ensemble of parametric estimators and a novel technique that includes conspecific spatial aggregation to an extended database of forest plots with up-to-date taxonomy. We show that the species abundance distribution of Amazonia is best approximated by a logseries with aggregated individuals, where aggregation increases with rarity. By averaging several methods to estimate total richness, we confirm that over 15,000 tree species are expected to occur in Amazonia. We also show that using ten times the number of plots would result in an increase to just ~50% of those 15,000 estimated species. To get a more complete sample of all tree species, rigorous field campaigns may be needed but the number of trees in Amazonia will remain an estimate for years to come.

Patrones de distribución de especies arbóreas de dosel y sotobosque a escala local en bosques de tierra firme, Amazonia colombiana / Distribution patterns of canopy and understory tree species at local scale in a Tierra Firme forest, the Colombian Amazonia

The effect of environmental variation on the structure of tree communities in tropical forests is still under debate. There is evidence that in landscapes like Tierra Firme forest, where the environmental gradient decreases at a local level, the effect of soil on the distribution patterns of plant species is minimal, happens to be random or is due to biological processes. In contrast, in studies with different kinds of plants from tropical forests, a greater effect on floristic composition of varying soil and topography has been reported. To assess this, the current study was carried out in a permanent plot of ten hectares in the Amacayacu National Park, Colombian Amazonia. To run the analysis, floristic and environmental variations were obtained according to tree species abundance categories and growth forms. In order to quantify the role played by both environmental filtering and dispersal limitation, the variation of the spatial configuration was included. We used Detrended Correspondence Analysis and Canonical Correspondence Analysis, followed by a variation partitioning, to analyze the species distribution patterns. The spatial template was evaluated using the Principal Coordinates of Neighbor Matrix method. We recorded 14 074 individuals from 1 053 species and 80 families. The most abundant families were Myristicaceae, Moraceae, Meliaceae, Arecaceae and Lecythidaceae, coinciding with other studies from Northwest Amazonia. Beta diversity was relatively low within the plot. Soils were very poor, had high aluminum concentration and were predominantly clayey. The floristic differences explained along the ten hectares plot were mainly associated to biological processes, such as dispersal limitation. The largest proportion of community variation in our dataset was unexplained by either environmental or spatial data. In conclusion, these results support random processes as the major drivers of the spatial variation of tree species at a local scale on Tierra Firme forests of Amacayacu National Park, and suggest reserve´s size as a key element to ensure the conservation of plant diversity at both regional and local levels.

El efecto de la variación ambiental en la estructura de las comunidades arbóreas en bosques tropicales, aún se debate. En paisajes como los bosques de tierra firme, donde el gradiente ambiental disminuye, el efecto de los suelos sobre los patrones de distribución de especies es mínimo. En contraste, un mayor efecto de la variación edáfica y topográfica sobre la composición florística, se ha reportado en estudios con diferentes tipos de plantas en bosques tropicales. Este estudio se realizó en diez hectáreas de una parcela permanente. Se evaluó el efecto de la variación ambiental y la configuración espacial sobre los patrones florísticos de las especies arbóreas a escala local, según el estado de desarrollo y categorías de abundancia relativa. Se registraron 14 074 individuos de 1 053 especies y 80 familias. Los suelos son ácidos, presentan altas concentraciones de Aluminio y son predominantemente arcillosos. La diversidad beta fue baja. Las diferencias florísticas explicadas fueron asociadas con procesos biológicos espacialmente estructurados, particularmente, con la limitación en dispersión. Aunque, la mayor parte de la variación no fue explicada por las variables consideradas. Estos resultados sugieren que procesos aleatorios son determinantes esenciales de la variación florística en bosques de tierra firme de la amazonia.

Hyperdominance in the Amazonian tree flora.

The vast extent of the Amazon Basin has historically restricted the study of its tree communities to the local and regional scales. Here, we provide empirical data on the commonness, rarity, and richness of lowland tree species across the entire Amazon Basin and Guiana Shield (Amazonia), collected in 1170 tree plots in all major forest types. Extrapolations suggest that Amazonia harbors roughly 16,000 tree species, of which just 227 (1.4%) account for half of all trees. Most of these are habitat specialists and only dominant in one or two regions of the basin. We discuss some implications of the finding that a small group of species--less diverse than the North American tree flora--accounts for half of the world's most diverse tree community.

[Soil and forest structure in the Colombian Amazon]. / Relación entre suelos y estructura del bosque en la Amazonía colombiana.

Forests structural differences could result of environmental variations at different scales. Because soils are an important component of plant's environment, it is possible that edaphic and structural variables are associated and that, in consequence, spatial autocorrelation occurs. This paper aims to answer two questions: (1) are structural and edaphic variables associated at local scale in a terra firme forest of Colombian Amazonia? and (2) are these variables regionalized at the scale of work? To answer these questions we analyzed the data of a 6ha plot established in a terra firme forest of the Amacayacu National Park. Structural variables included basal area and density of large trees (diameter > or = 10cm) (Gdos and Ndos), basal area and density of understory individuals (diameter < 10cm) (Gsot and Nsot) and number of species of large trees (sp). Edaphic variables included were pH, organic matter, P, Mg, Ca, K, Al, sand, silt and clay. Structural and edaphic variables were reduced through a principal component analysis (PCA); then, the association between edaphic and structural components from PCA was evaluated by multiple regressions. The existence of regionalization of these variables was studied through isotropic variograms, and autocorrelated variables were spatially mapped. PCA found two significant components for structure, corresponding to the structure of large trees (G, Gdos, Ndos and sp) and of small trees (N, Nsot and Gsot), which explained 43.9% and 36.2% of total variance, respectively. Four components were identified for edaphic variables, which globally explained 81.9% of total variance and basically represent drainage and soil fertility. Regression analyses were significant (p < 0.05) and showed that the structure of both large and small trees is associated with greater sand contents and low soil fertility, though they explained a low proportion of total variability (R2 was 4.9% and 16.5% for the structure of large trees and small tress, respectively). Variables with spatial autocorrelation were the structure of small trees, Al, silt, and sand. Among them, Nsot and sand content showed similar patterns of spatial distribution inside the plot.

Relación entre suelos y estructura del bosque en la Amazonía colombiana

Soil and forest structure in the Colombian Amazon. Forests structural differences could result of environmental variations at different scales. Because soils are an important component of plant’s environment, it is possible that edaphic and structural variables are associated and that, in consequence, spatial autocorrelation occurs. This paper aims to answer two questions: (1) are structural and edaphic variables associated at local scale in a terra firme forest of Colombian Amazonia? and (2) are these variables regionalized at the scale of work? To answer these questions we analyzed the data of a 6ha plot established in a terra firme forest of the Amacayacu National Park. Structural variables included basal area and density of large trees (diameter≥10cm) (Gdos and Ndos), basal area and density of understory individuals (diameter<10cm) (Gsot and Nsot) and number of species of large trees (sp). Edaphic variables included were pH, organic matter, P, Mg, Ca, K, Al, sand, silt and clay. Structural and edaphic variables were reduced through a principal component analysis (PCA); then, the association between edaphic and structural components from PCA was evaluated by multiple regressions. The existence of regionalization of these variables was studied through isotropic variograms, and autocorrelated variables were spatially mapped. PCA found two significant components for structure, corresponding to the structure of large trees (G, Gdos, Ndos and sp) and of small trees (N, Nsot and Gsot), which explained 43.9% and 36.2% of total variance, respectively. Four components were identified for edaphic variables, which globally explained 81.9% of total variance and basically represent drainage and soil fertility. Regression analyses were significant (p<0.05) and showed that the structure of both large and small trees is associated with greater sand contents and low soil fertility, though they explained a low proportion of total variability (R² was 4.9% and 16.5% for the structure of large trees and small tress, respectively). variables with spatial autocorrelation were the structure of small trees, Al, silt, and sand. Among them, Nsot and sand content showed similar patterns of spatial distribution inside the plot. Rev. Biol. Trop. 59 (3): 1307-1322. Epub 2011 September 01.

Las diferencias estructurales del bosque pueden ser el producto de variaciones ambientales a diferentes escalas, entre ellas los suelos. Para evaluar tal asociación, se usaron los datos de estructura del bosque y de suelos de una parcela de 6ha establecida en un bosque de tierra firme de la Amazonía colombiana. Las variables edáficas y estructurales se redujeron con un análisis de componentes principales (ACP) y un análisis de regresión múltiple verificó si existía asociación entre los componentes edáficos y estructurales del ACP. La regionalización de las variables de estudio se verificó con variogramas isotrópicos; además, se construyeron mapas de distribución espacial. El ACP de las variables estructurales identificó dos componentes: dosel y sotobosque, los cuales explicaron el 43.9 y 36.2% de la varianza total, respectivamente; para las variables edáficas los cuatro primeros componentes explicaron globalmente el 81.9% de la varianza total. Los análisis de regresión mostraron que tanto el dosel como el sotobosque se asocian con mayores contenidos de arena y baja fertilidad del suelo (p<0.05), pero explicaron una proporción baja de la variabilidad total (R²=4.9% para dosel y 16.5% para sotobosque). Las tres variables de la estructura del sotobosque, Al, limo y arena presentaron autocorrelación espacial.

Variación florística de especies arbóreas a escala local en un bosque de tierra firme en la Amazonia colombiana

El presente estudio se llevó a cabo en cinco hectáreas de una parcela permanente establecida en el Parque Nacional Amacayacu, Amazonia colombiana. En éste, se evaluó el efecto de la variación ambiental y la configuración espacial sobre los patrones florísticos de las especies arbóreas (DAP>10 cm) a escala local en un bosque de tierra firme. Se estudió la variación florística y ambiental en cuadrantes de 20x20 m. Adicionalmente, se consideraron diferentes categorías de abundancia (total, alta, media y baja). Se utilizó el Análisis de Correspondencia Linealizado y el Análisis de Correspondencia Canónica, seguido de una partición de la variación, para cuantificar la magnitud a la cual el ambiente y la limitación en dispersión determinan la variación florística. La fracción espacial, representando procesos de autocorrelación como la limitación en dispersión, se analizó mediante dos métodos: Asumiendo un polinomio de tercer grado y por el método de Coordenadas Principales de Matrices Vecinas (PCNM). La diversidad beta de la parcela fue baja. El PCNM aparece como el método de análisis más apropiado para estudios a esta escala. Las diferencias florísticas explicadas a lo largo de la parcela de 5-ha fueron principalmente asociadas con procesos biológicos como la limitación en dispersión. La mayor parte de la variación florística, no obstante, no fue explicada por las variables ambientales o espaciales consideradas. En conclusión, estos resultados sugieren que procesos aleatorios son determinantes esenciales de la variación espacial de las especies arbóreas a escala local en tierra firme en los bosques en el Parque Nacional Amacayacu.

This study was carried out in a 5-ha permanent plot established in the Amacayacu National Park, Colombian Amazonia. We assessed the extent at which floristic patterns of tree species were determined by either the environmental variation or the spatial configuration in tierra firme forests. Floristic and environmental variation was assessed on quadrants of 20x20 m. To run the analysis, four different categories of abundance (all, high, medium and low) were considered. We used Detrended Correspondence Analysis and Canonical Correspondence Analysis, followed by a variation partitioning, to analyze the patterns of species distribution in order to quantify the role played by both environmental filtering and dispersal limitation. The spatial template, which represents dispersal limitation, was evaluated in two different ways: using a third degree polynomial and using the Principal Coordinates of Neighbour Matrix (PCNM) method. Beta diversity was relatively low within the plot. PCNM appears as the most appropriate method to analyze the spatial template at this scale. The floristic differences explained along the 5-ha plot were mainly associated to biological processes, such as dispersal limitation. The largest proportion of community variation in our dataset was unexplained by either environmental or spatial data. In conclusion, these results support random processes as the major drivers of the spatial variation of tree species at a local scale on tierra firme forests in the Amacayacu National Park.