Estimating the global conservation status of more than 15,000 Amazonian tree species.

Estimates of extinction risk for Amazonian plant and animal species are rare and not often incorporated into land-use policy and conservation planning. We overlay spatial distribution models with historical and projected deforestation to show that at least 36% and up to 57% of all Amazonian tree species are likely to qualify as globally threatened under International Union for Conservation of Nature (IUCN) Red List criteria. If confirmed, these results would increase the number of threatened plant species on Earth by 22%. We show that the trends observed in Amazonia apply to trees throughout the tropics, and we predict that most of the world's >40,000 tropical tree species now qualify as globally threatened. A gap analysis suggests that existing Amazonian protected areas and indigenous territories will protect viable populations of most threatened species if these areas suffer no further degradation, highlighting the key roles that protected areas, indigenous peoples, and improved governance can play in preventing large-scale extinctions in the tropics in this century.

Fine litter input to terrestrial humus forms in Colombian Amazonia.

A comparative litter fall study was made in five rain forest stands along a gradient of humus form development and soils in the Amazon lowlands of eastern Colombia. The total fine litter fall was highest in a plot on a well drained soil of the flood plain of the Caquetá River (1.07 kg · m-2 · y-1), lower in three plots on well drained upland soils (0.86, 0.69, and 0.68 kg · m-2 · y-1), and lowest in a plot on a poorly drained, upland podzolised soil (0.62 kg · m-2 · y-1). In the four upland plots, leaf litter fall patterns were highly associated, which points at climatic regulation. Litter resource quality, as represented by nutrient concentrations and area/weight ratio of the leaf litter fall, was comparatively high in the flood plain plot. In the upland plots, concentrations and fluxes of Ca, Mg, K, and P were as low as in oligotrophic central Amazonian upland forests. This questions generalisations that the western peripheral region of the Amazon basin should be less oligotrophic than central Amazonia. The upland plot on the podzolised soil showed the lowest concentrations and fluxes of N. Mean residence times of organic matter and nutrients in the L horizons hardly differed between the five plots, suggesting that edaphic properties and litter resource quality are of little importance in the first step of decomposition. Mean residence time of organic matter in all ectorganic horizons combined (estimated on the basis of litter input and necromass on the forest floor, and uncorrected for dead fine root input) varied from 1.0 y in the flood plain forest, 1.1-3.3 y in the well drained upland forests, and 10.2 y in the forest on the podzolised soil.

Metal leaching, acidity, and altitude confine benthic macroinvertebrate community composition in Andean streams.

Andean streams drain metal-rich bedrock and are subjected to an extreme altitude gradient, which may create highly selective conditions for life. The aim of the present study was to evaluate the combined effects of metals and altitude on benthic macroinvertebrate community composition in Andean streams. Metal-rich sites were characterized by high metal concentrations and low pH, and high-altitude sites were characterized by high ultraviolet-B radiation and low concentrations of dissolved organic matter. Canonical correspondence analysis indicated that the patterns in faunal composition were best explained by metals followed by altitude, with dipterans and collembolans occurring mostly under harsh conditions of high altitude and high metal levels. Interaction between metals and altitude was most evident at metal-rich sites. It is suggested that in Andean streams, metal leaching from igneous rock and altitude may be important factors confining benthic macroinvertebrate communities, reducing their numbers and changing their composition toward specialized taxa.

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.

Metal-induced shifts in benthic macroinvertebrate community composition in Andean high altitude streams.

High altitude creates unique challenging conditions to biota that limit the diversity of benthic communities. Because environmental pollution may add further stress to life at high altitude, the present study explored the effect of metal pollution on the macroinvertebrate community composition in Andean streams between 3,500 to 4,500 meters above sea level (masl) during wet and dry seasons. At polluted sites, showing a high conductivity and a low pH, metal concentrations (e.g., Al, 13.07 mg/L; As, 3.49 mg/L; Mn, 19.65 mg/L; Pb, 0.876 mg/L; Zn, 16.08 mg/L) ranged from 8-fold up to 3,500-fold higher than at reference sites. The cumulative criterion unit allowed quantifying the potential toxicity of metal mixtures at the contaminated sites. Principal component analysis of physical chemical variables showed that reference sites were more likely to be structured by transparency, water discharge, and current velocity, while polluted sites appeared to be determined by metals and conductivity. Canonical correspondence analysis indicated a strong influence of highly correlated metals in structuring invertebrate communities, which were dominated by dipterans, coleopterans, collembolans, and mites at polluted sites. At reference sites crustaceans, ephemeropterans, plecopterans, and trichopterans were the most representative taxa. We concluded that severe metal pollution induced changes in macroinvertebrate community composition in high-altitude Andean streams, with a replacement of sensitive taxa by more tolerant taxa. Yet relatively species-rich communities persisted under harsh conditions.

Response of pollen diversity to the climate-driven altitudinal shift of vegetation in the Colombian Andes.

Change in diversity of fossil pollen through time is used as a surrogate for biodiversity history. However, there have been few studies to explore the sensitivity of the measured pollen diversity to vegetation changes and the relationship between pollen diversity and plant diversity. This paper presents results of a study to assess the relationship between pollen diversity and relative abundance of pollen from different altitudinal vegetation belts (subandean forest, Andean forest, subparamo and grassparamo) in three records from the tropical Andes in Colombia. The results indicated that plant diversity in the vegetation declined with altitude and pollen diversity is positively correlated to the abundance of pollen from lower altitude vegetation belts and negatively correlated to that from the grassparamo. These results, therefore, suggest that pollen diversity coarsely reflects the diversity of the surrounding vegetation. Using this interpretation, we were able to predict changes in plant diversity over the past 430000 years in the Colombian Andes. Results indicated that under warmer climatic conditions, more species-diverse vegetation of low elevation moved upslope to contribute more pollen diversity to the study sites, and under colder conditions, species-poor grassparamo moved downslope and observed pollen diversity was lower. This study concludes that fossil pollen diversity may provide an important proxy to reconstruct the temporal changes in plant diversity.