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Abstract: Litter fall and leaf decomposition represent important functional processes, yet we have a limited understanding of these processes in disturbed and regenerating tropical habitats. Litter production, litterfall phenology and leaf decomposition were examined in primary forests, 14–19-year-old secondary forests and 4–5-year-old Eucalyptus urophylla plantations in the north-east Brazilian Amazon. Total annual litter fall was similar in primary and secondary forests, and lower in plantations. Leaf fall in primary and secondary forests was negatively associated with rainfall, and was highest in the dry season. Leaf fall in Eucalyptus plantations showed an opposite response, and peaked during the wet season. Decomposition experiments were carried out in the three habitats using 1200 litter bags (1mm mesh) filled separately with leaves from four different species of tree, including an exotic plantation species (E. urophylla) and trees typical of secondary (Bellucia spp. and Vismia spp.) and primary forests (Bertholettia excelsa). Litter bags were re-weighed at 3-month intervals 3, 6, 9 and 12 months after being placed on the forest floor. A repeated measures General Linear Model showed that litter decomposition was similar in the primary and secondary forest, and slowest in the Eucalyptus plantations. Leaves decomposed, from fastest to slowest, in the following order: E. urophylla > B. excelsa > Vismia spp.> Bellucia spp. There was no significant interaction between leaf species and habitat type. Our results indicate that secondary forests regenerating on abandoned and degraded Amazonian lands can be effective at restoring ecosystem processes such as litterfall and decomposition. [Copyright &y& Elsevier]

Studies the variation of the species composition and structure of a forest flooded by a clear water river in Eastern Amazonia, Brazil. Variation in the water level fluctuations of rivers in the Amazonian region; estimation of total basal area in the forest; Correlation of species composition with water type and soil condition.

In recent years, scientists have identified critical threats posed to the forests of Amazonia by the Brazilian government's plans to dramatically expand highways and other major infrastructure projects in the region. Conclusions have been disputed by elements of the Brazilian government, which assert that a key assumption of our spatial models — that new roads and highways will continue to promote large-scale Amazonian deforestation, as they have done in the past — no longer applies. This is so, they argue, because of improvements in frontier governance and environmental-law enforcement, as well as changes in Brazilian public attitudes toward forests. As a consequence, the Brazilian government is proceeding with the largest expansion of highways, roads, power lines, gas lines, hydroelectric reservoirs, railroads, and river-channelization projects in the history of the Amazonia.

For more than three decades, major efforts in sampling and analyzing tree diversity in South America have focused almost exclusively on trees with stems of at least 10 and 2.5 cm diameter, showing highest species diversity in the wetter western and northern Amazon forests. By contrast, little attention has been paid to patterns and drivers of diversity in the largest canopy and emergent trees, which is surprising given these have dominant ecological functions. Here, we use a machine learning approach to quantify the importance of environmental factors and apply it to generate spatial predictions of the species diversity of all trees (dbh ≥ 10 cm) and for very large trees (dbh ≥ 70 cm) using data from 243 forest plots (108,450 trees and 2832 species) distributed across different forest types and biogeographic regions of the Brazilian Amazon. The diversity of large trees and of all trees was significantly associated with three environmental factors, but in contrasting ways across regions and forest types. Environmental variables associated with disturbances, for example, the lightning flash rate and wind speed, as well as the fraction of photosynthetically active radiation, tend to govern the diversity of large trees. Upland rainforests in the Guiana Shield and Roraima regions had a high diversity of large trees. By contrast, variables associated with resources tend to govern tree diversity in general. Places such as the province of Imeri and the northern portion of the province of Madeira stand out for their high diversity of species in general. Climatic and topographic stability and functional adaptation mechanisms promote ideal conditions for species diversity. Finally, we mapped general patterns of tree species diversity in the Brazilian Amazon, which differ substantially depending on size class., (© 2023 John Wiley & Sons Ltd.)

The fate of tropical forests under future climate change is dependent on the capacity of their trees to adjust to drier conditions. The capacity of trees to withstand drought is likely to be determined by traits associated with their hydraulic systems. However, data on whether tropical trees can adjust hydraulic traits when experiencing drought remain rare. We measured plant hydraulic traits (e.g. hydraulic conductivity and embolism resistance) and plant hydraulic system status (e.g. leaf water potential, native embolism and safety margin) on >150 trees from 12 genera (36 species) and spanning a stem size range from 14 to 68 cm diameter at breast height at the world's only long-running tropical forest drought experiment. Hydraulic traits showed no adjustment following 15 years of experimentally imposed moisture deficit. This failure to adjust resulted in these drought-stressed trees experiencing significantly lower leaf water potentials, and higher, but variable, levels of native embolism in the branches. This result suggests that hydraulic damage caused by elevated levels of embolism is likely to be one of the key drivers of drought-induced mortality following long-term soil moisture deficit. We demonstrate that some hydraulic traits changed with tree size, however, the direction and magnitude of the change was controlled by taxonomic identity. Our results suggest that Amazonian trees, both small and large, have limited capacity to acclimate their hydraulic systems to future droughts, potentially making them more at risk of drought-induced mortality., (© 2020 John Wiley & Sons Ltd.)