Rarity of monodominance in hyperdiverse Amazonian forests.

Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such "monodominant" forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees ≥ 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors

Amazonia

The Amazonia series interweaves scientific, aesthetic and cultural paradigms to offer insights into the huge diversity of living organisms and the space they occupy in the planet’s evolution. It resulted from research conducted in the Natural History Museum, London and a field expedition to the Peruvian Amazon. The primary inquiry, based on the theory of operational aesthetics, was to investigate how contemporary art can act as a trigger to provoke a deeper appreciation of the natural world and to understand the importance of biodiversity and the effects its loss will have on climate change. The thirty-seven commissioned artefacts in different media and formats were specifically created for the Jerwood Gallery at the Natural History Museum to stimulate different sensations and provoke different audience responses. The artworks focused attention on the myriad of species that depend on the eco-equilibrium of the Amazon and prompted the public to reflect on the fragile balance and coexistence of this environment. As part of the commissioning process the researchers engaged with the museum collections including entomology, botany, palaeontology and the library archive as well as accompanying scientists on the field trip to the Amazon. This led to a distinctive range of approaches, including macrophotographs, a diptych video projection, and three 1:1 porcelain sculpture casts of dinosaur fossils. The exhibition was funded by the Natural History Museum of London Contemporary Art Program to coincide with the International Year of Biodiversity

Height-diameter allometry of tropical forest trees

Tropical tree height-diameter (H:D) relationships may vary by forest type and region making large-scale estimates of above-ground biomass subject to bias if they ignore these differences in stem allometry. We have therefore developed a new global tropical forest database consisting of 39 955 concurrent H and D measurements encompassing 283 sites in 22 tropical countries. Utilising this database, our objectives were: 1. to determine if H:D relationships differ by geographic region and forest type (wet to dry forests, including zones of tension where forest and savanna overlap). 2. to ascertain if the H:D relationship is modulated by climate and/or forest structural characteristics (e.g. stand-level basal area, A). 3. to develop H:D allometric equations and evaluate biases to reduce error in future local-to-global estimates of tropical forest biomass. Annual precipitation coefficient of variation (PV), dry season length (SD), and mean annual air temperature (TA) emerged as key drivers of variation in H:D relationships at the pantropical and region scales. Vegetation structure also played a role with trees in forests of a high A being, on average, taller at any given D. After the effects of environment and forest structure are taken into account, two main regional groups can be identified. Forests in Asia, Africa and the Guyana Shield all have, on average, similar H:D relationships, but with trees in the forests of much of the Amazon Basin and tropical Australia typically being shorter at any given D than their counterparts elsewhere. The region-environment-structure model with the lowest Akaike\u27s information criterion and lowest deviation estimated stand-level H across all plots to within amedian −2.7 to 0.9% of the true value. Some of the plot-to-plot variability in H:D relationships not accounted for by this model could be attributed to variations in soil physical conditions. Other things being equal, trees tend to be more slender in the absence of soil physical constraints, especially at smaller D. Pantropical and continental-level models provided less robust estimates of H, especially when the roles of climate and stand structure in modulating H:D allometry were not simultaneously taken into account

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Increasing biomass in Amazonian forest plots

A previous study by Phillips et al. of changes in the biomass of permanent sample plots in Amazonian forests was used to infer the presence of a regional carbon sink. However, these results generated a vigorous debate about sampling and methodological issues. Therefore we present a new analysis of biomass change in old-growth Amazonian forest plots using updated inventory data. We find that across 59 sites, the above-ground dry biomass in trees that are more than 10 cm in diameter (AGB) has increased since plot establishment by 1.22 ± 0.43 Mg per hectare per year (ha-1 yr-1), where 1 ha = 104 m2), or 0.98 ± 0.38 Mg ha-1 yr-1 if individual plot values are weighted by the number of hectare years of monitoring. This significant increase is neither confounded by spatial or temporal variation in wood specific gravity, nor dependent on the allometric equation used to estimate AGB. The conclusion is also robust to uncertainty about diameter measurements for problematic trees: for 34 plots in western Amazon forests a significant increase in AGB is found even with a conservative assumption of zero growth for all trees where diameter measurements were made using optical methods and/or growth rates needed to be estimated following fieldwork. Overall, our results suggest a slightly greater rate of net stand-level change than was reported by Phillips et al. Considering the spatial and temporal scale of sampling and associated studies showing increases in forest growth and stem turnover, the results presented here suggest that the total biomass of these plots has on average increased and that there has been a regional-scale carbon sink in old-growth Amazonian forests during the previous two decades

Bryophyte diversity patterns in flooded and tierra firme forests in the Araracuara Region, Colombian Amazonia

We investigated patterns of bryophyte species richness and composition in two forest types of Colombian Amazonia, non-flooded tierra firme forest and floodplain forest of the Caquetá River. A total of 109 bryophyte species were recorded from 14 0.2 ha plots. Bryophyte life forms and habitats were analyzed, including the canopy and epiphylls. Bryophyte species did not show significant differences between landscapes but mosses and liverworts were different and with opposite responses balancing the overall richness. Independence test showed differences in both life form and habitat use distribution between the two forest types with more fan and mat bryophytes species in the floodplains, and more epiphytic liverworts in the tierra firme forest. Correspondence analysis showed differences in the bryophyte species assemblage between the two forest types where they may be responding to the higher humidity provided by the flooding. Despite of, the environmental differences detected, epiphyll species assemblages were not strongly affected. Apparently, epiphyll habitat is stressful enough to hide the environmental differences between the flooded and Tierra firme forests.Investigamos los patrones de riqueza de especies y composición florística de briofitos en dos tipos de bosque en la Amazonía Colombiana. Bosques no inundados de Tierra firme y bosques periódicamente inundados en los planos inundables del Rió Caquetá. Encontramos 109 especies de briofitos en 14 parcelas de 0.2 ha. Nosotros analizamos diferencias en la distribución de formas de vida y hábitat de los briofitos entre los dos tipos de bosque incluyendo especies del dosel y epifilas. El número de especies de briofitos no mostró diferencias significativas entre los dos tipos de bosque. Pero musgos y hepáticas si tuvieron diferencias con respuestas opuestas balanceando el número total de especies. Pruebas de independencia mostraron diferencias en la distribución de formas de vida y uso de hábitat entre los dos tipos de bosque con más especies de abanicos y esteras en los planos inundables, y más especies de hepáticas epifitas en el bosque de Tierra firme. El análisis de correspondencia mostró diferencias en la composición florística de briofitos entre ambos tipos de bosque, donde las comunidades de briofitos pueden estar respondiendo a un gradiente de humedad aportada por la inundación periódica de los planos inundables. La composición florística de los briofitos epifilos no mostró una separación tan clara entre los tipos de bosque como si fue detectada en los otros hábitat donde los briofitos fueron encontrados. Aparentemente, el hábitat epifilo es suficientemente estresante para ocultar el efecto de las diferentes condiciones ambientales de los bosques inundables y de Tierra firme

Changes in the carbon balance of tropical forest: evidence from long-term plots

The role of the world’s forests as a “sink” for atmospheric carbon dioxide is the subject of active debate. Long-term monitoring of plots in mature humid tropical forests concentrated in South America revealed that biomass gain by tree growth exceeded losses from tree death in 38 out of 50 neotropical sites. These forest plots have accumulated 0.71 + 0.34 tons of carbon per hectare per year in recent decades. The data suggest that neotropical forests may be a significant carbon sink, reducing the rate of increase in atmospheric CO2

Environmental Costs of Government-Sponsored Agrarian Settlements in Brazilian Amazonia

Brazil has presided over the most comprehensive agrarian reform frontier colonization program on Earth, in which ~1.2 million settlers have been translocated by successive governments since the 1970's, mostly into forested hinterlands of Brazilian Amazonia. These settlements encompass 5.3% of this ~5 million km2 region, but have contributed with 13.5% of all land conversion into agropastoral land uses. The Brazilian Federal Agrarian Agency (INCRA) has repeatedly claimed that deforestation in these areas largely predates the sanctioned arrival of new settlers. Here, we quantify rates of natural vegetation conversion across 1911 agrarian settlements allocated to 568 Amazonian counties and compare fire incidence and deforestation rates before and after the official occupation of settlements by migrant farmers. The timing and spatial distribution of deforestation and fires in our analysis provides irrefutable chronological and spatially explicit evidence of agropastoral conversion both inside and immediately outside agrarian settlements over the last decade. Deforestation rates are strongly related to local human population density and road access to regional markets. Agrarian settlements consistently accelerated rates of deforestation and fires, compared to neighboring areas outside settlements, but within the same counties. Relocated smallholders allocated to forest areas undoubtedly operate as pivotal agents of deforestation, and most of the forest clearance occurs in the aftermath of government-induced migration

Do the recent severe droughts in the Amazonia have the same period of length?

We propose a new measure based on drought period length to assess the temporal difference between the recent two severe droughts of 2005 and 2010 in the Amazonia. The sensitivity of the measure is demonstrated by disclosing the distinct spatial responding mechanisms of the Northeastern and Southwestern Amazon (NA, SA) to the surrounding sea surface temperature (SST) variabilities. The Pacific and Atlantic oceans have different roles on the precipitation patterns in Amazonia. More specifically, the very dry periods in the NA are influenced by El Ni\~no events, while the very dry periods in the SA are affected by the anomalously warming of the SST in the North Atlantic. We show convincingly that the drought 2005 hit SA, which is caused by the North Atlantic only. There are two phases in the drought 2010: (i) it was started in the NA in August 2009 affected by the El Ni\~no event, and (ii) later shifted the center of action to SA resulted from anomalously high SST in North Atlantic, which further intensifies the impacts on the spatial coverage.Comment: 5 figure