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.

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.

Spatial distribution pattern and diameter structure of Protium Burm. f. in Iratapuru river sustainable development reserve, Amapá, Brazil / Padrão de distribuição espacial e estrutura diamétrica de Protium Burm. f. na reserva de desenvolvimento sustentável do Rio Iratapuru, Amapá, Brasil

The present work aims to determine the spatial distribution pattern of Protium Burm. f and the diametric structure of these species in a dense tropical submontane rainforest along the Sustainable Development Reserve (SDR) of the Iratapuru river. The area of study was divided into three plateau compartments called Mane Preto Sierra, Banco Grande Sierra and Alaska Sierra. In each plateau compartment it was settled a single area transect with 1,000 x 20 m, where DAP ≥ 10 cm of the entire Protium population within the transects was measured. The data was processed in the specific software Mata Nativa 2. There were inventoried Protium tenuifolium, Protium altsoni, Protium polybotryum subsp. blackii and Protium paniculatum var. riedelianum. Most individuals concentrated in smaller diametric classes, decreasing progressively to a lesser extent in larger classes. It can be concluded that the population has medium size and its vertical structure is characterized by the presence of three strata, however, its phytocenoses is defined by two clear constants: the first groups individuals of up to 15 m of height and forms the uniform and dominant stratum; the second is composed by emerging up to 35 m high and whose diameter structure shows a population in dynamic balance.

Este trabalho tem como objetivo determinar o padrão de distribuição espacial de Protium Burm. f e estrutura diamétrica dessas espécies em uma floresta tropical densa submontana ao longo da reserva de desenvolvimento sustentável (RDS) do rio Iratapuru. A área estudada foi dividida em três compartimentos de planaltos denominados Serra Mane Preto, Serra Banco Grande e Serra Alaska. Em cada compartimento de planalto instalou-se transecto de área única com 1.000 x 20 m, onde foi mensurado o DAP ≥ 10 cm de toda população de Protium dentro dos transectos. Os dados foram processados em softwares específicos Mata Nativa 2. Foram inventariados Protium tenuifolium, Protium altsonii, Protium polybotryum subsp. blackii e Protium paniculatum var. riedelianum. A maior parte dos indivíduos concentrou-se nas menores classes diamétricas, diminuindo progressivamente até atingir menor proporção nas maiores classes. Pode-se concluir que a população apresenta porte mediano, sua estrutura vertical caracteriza-se pela presença de três estratos; no entanto, sua fitocenose define-se por dois contínuos bem evidentes; o primeiro agrupa indivíduos com até 15 m de altura e forma o estrato uniforme e dominante; o segundo é composto por emergentes com até 35 m de altura e que a estrutura diamétrica evidencia uma população em equilíbrio dinâmico.

Composition, structure and floristic diversity in dense rain forest in the Eastern Amazon, Amapá, Brazil / Composição, estrutura e diversidade florística em floresta ombrófila densa na Amazônia Oriental, Amapá, Brasil

This study aims to evaluate the phytosociology and floristic composition of tree species in the eastern Amazon, at the Iratapuru River Sustainable Development Reserve (RDS), State of Amapá. Fouteen quarters with dimensions of 100 m x 100 m were randomly inventoried, and 50 sub-plots of 10 m x 20 m were established. In each sub-plot all living individuals were sampled, being taken from the height data and DAP (breast height diameter) for tree species ≥ 10 cm. A total of 5,233 individuals belonging to 33 families and 184 species were registered. The families with the largest number of species were Fabaceae (32), Lauraceae (17), Sapotaceae (12), Moraceae (10), Lecythidaceae (8) and Annonaceae (8). The six most abundant families (18.18% of total families) in the present study were responsible for more than half (57.92%) of the total number of species. The floristic structure of the area studied was diverse, with species of varied interests, including: medicinal, timber and oil-producing.

Este trabalho objetiva avaliar a composição florística e a fitossociologia de espécies arbóreas na Amazônia Oriental, Reserva de Desenvolvimento Sustentável do Rio Iratapuru, Estado do Amapá. Foram inventariados 14 quadrantes de 100 m x 100 m distribuídos aleatoriamente, onde se estabeleceram 50 sub-parcelas de 10 m x 20 m. Em cada sub-parcela foram amostrados todos os indivíduos vivos, sendo tomados dados de altura e DAP (diâmetro a altura do peito) para espécies arbóreas ≥10 cm. Foram registrados 5.233 indivíduos distribuídos em 33 famílias e 184 espécies. As famílias com maior número de espécies foram Fabaceae (17), Lauraceae (17), Sapotaceae (12), Moraceae (10), Lecythidaceae (8) e Annonaceae (8). Essas seis famílias mais abundantes (18,18% total das famílias) presentes no estudo foram responsáveis por mais da metade (57,92%) do número total de espécies. A estrutura florística da área estudada mostrou-se diversificada, apresentando espécies de interesses variados, como medicinal, madeireira e oleífera.