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International audienceAccurately determining biomass of large trees is crucial for reliable biomass analyses in most tropical forests, but most allometric models calibration are deficient in large trees data. This issue is a major concern for high-biomass mangrove forests, especially when their role in the ecosystem carbon storage is considered. As an alternative to the fastidious cutting and weighing measurement approach, we explored a non-destructive terrestrial laser scanning approach to estimate the aboveground biomass of large mangroves (diameters reaching up to 125 cm). Because of buttresses in large trees, we propose a pixel-based analysis of the composite 2D flattened images, obtained from the successive thin segments of stem point-cloud data to estimate wood volume. Branches were considered as successive best-fitted primitive of conical frustums. The product of wood volume and height-decreasing wood density yielded biomass estimates. This approach was tested on 36 A. germinans trees in French Guiana, considering available biomass models from the same region as references. Our biomass estimates reached ca. 90% accuracy and a correlation of 0.99 with reference biomass values. Based on the results, new tree biomass model, which had R² of 0.99 and RSE of 87.6 kg of dry matter. This terrestrial LiDAR-based approach allows the estimates of large tree biomass to be tractable, and opens new opportunities to improve biomass estimates of tall mangroves. The method could also be tested and applied to other tree species

The Amazon River delta may be currently characterized biophysically as a relatively preserved delta compared to the rampant vulnerability of many of the world’s large deltas. This status of relative preservation is reflected in a number of criteria: The still largely free-flowing nature of many of the rivers and the main stem of the Amazon that feed the delta in sediment, exceptional biodiversity, dominant shoreline accretion, and the absence of anthropogenically-generated subsidence. In this review, we show that these relatively reassuring conditions are progressively being called into question by the effects of dams on fluvial sediment supply to the delta, by increasing demographic, urban, and land development pressures in this still largely underpopulated delta, and by problems of governance that underplay aspects of basin-wide and deltaic environmental deterioration. A major challenge is that of bringing together these contrasting demands that are leading to the emergence of zones of environmental stress that test the resilience of this delta. An integral part of the strategy for the analysis of collective action, management, and conservation is that of considering the Amazon delta in terms of interacting socio-ecological systems. Pressures on the delta will be compounded in the future by decreasing fluvial sediment supply and sea-level rise. Although climate change is projected to generate surplus sediment, the rapid growth of dam constructions upstream of the delta will negatively impact the river’s sediment flux. Conservation and management of the Amazon River system aimed at keeping the delta resilient in the context of sea-level rise and reduction of sediment supply will require clear governance and better planning and anticipation, as well as socio-ecological integration. These are also requirements that will need to be implemented in the 1500 km-long coastal zone of the Guianas countries located west of the Amazon delta and the sediment dynamics and stability of which are largely determined by sediment supply from the Amazon.

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Lecythidaceae, Lauraceae and Vochysiaceae families were the most important of the studied population.

As áreas úmidas representam cerca de um terço da área do Estado do Amapá. cujos processos de inundação ainda não foram devidamente esclarecidos e podem causar situações de calamidade pública, durante o período de chuvas, em áreas com adensamento populacional, gerando diversos riscos à população e danos socioeconômicos. Este trabalho apresenta o mapeamento das áreas úmidas nas áreas urbanas, nas cidades de Macapá e Santana, com o intuito de reconhecer a dinâmica de inundação e processos associados. As áreas e  suas respectivas bacias hidrográficas foram mapeadas, aplicando critérios geomorfológicos utilizando um modelo digital de elevação superficial e um mosaico de imagens de sensores óticos de alta resolução. Trabalhos de campo foram realizados para identificar a rede de drenagem e suas nascentes e medir as variações no nível de água, em três pontos ao longo da bacia do Igarapé Fortaleza, nos períodos de máximos (março e maio) e mínimos (setembro e novembro) níveis d´água. As informações foram integradas em um Sistema de Informação Geográfica (SIG). Três conjuntos de áreas úmidas foram reconhecidas: os diques marginais, recobertos pelas florestas de várzeas; a planície de inundação com as áreas de pântanos, denominados localmente de "ressacas”; e um conjunto de canais de marés que bordejam a margem do rio Amazonas. Na planície de inundação, quinze sistemas de pântanos (“ressacas”) foram mapeados. Os resultados podem contribuir para implementação de políticas para monitoramento e mitigação dos riscos à inundação em bacias hidrográficas costeiras, os quais se agravarão com o quadro de mudanças climáticas previsto para o futuro próximo