The Balbina hydropower dam in the Central Amazon basin, established in the Uatumã River in the 1980s, is emblematic for its socio‐environmental disaster. Its environmental impacts go far beyond the reservoir and dam, however, affecting the floodplain forests (igapó) in the downstream area (dam shadow), which have been assessed using a transdisciplinary research approach, synthesized in this review. Floodplain tree species are adapted to a regular and predictable flood pulse, with high‐ and low‐water periods occurring during the year. This was severely affected by the operation of the Balbina dam, which caused the suppression of both the aquatic phase at higher floodplain elevations and the terrestrial phase at lower floodplain elevations (termed the ‘sandwich effect’). During the period of construction and reservoir fill, large‐scale mortality already occurred in the floodplains of the dam shadow as a result of reduced stream flow, in synergy with severe drought conditions induced by El Niño events, causing hydraulic failure and making floodplains vulnerable to wildfires. During the operational period of the dam, permanent flooding conditions at low topographical elevations resulted in massive tree mortality. So far, 12% of the igapó forests have died along a downstream river stretch of more than 125 km. As a result of flood suppression at the highest elevations, an encroachment of secondary tree species from upland (terra firme) forests occurred. More than 35 years after the implementation of the Balbina dam, the downstream impacts caused massive losses of macrohabitats, ecosystem services, and diversity of flood‐adapted tree species, probably cascading down to the entire food web, which must be considered in conservation management. These findings are discussed critically, emphasizing the urgent need for the Brazilian environmental regulatory agencies to incorporate downstream impacts in the environmental assessments of several dam projects planned for the Amazon region.

We carried out a comparative morphological study to evaluate the taxonomic value of seed and seedling traits of Entada polystachya and E. simplicata (Leguminosae, Mimosoideae, Mimoseae). Seeds of both species were collected from wild populations in Roraima State, Brazil. Our results show consistent quantitative and qualitative differences between these species regarding their seeds and seedlings. Testa fracture lines, funiculus impression, lens characters, radicle shape and length, and cotyledon lobes length, seedling morphology group, number of pinnae at first node, and hypocotyl length permit a straightforward distinction of E. polystachya from E. simplicata, supporting a recent treatment of the latter taxon as a distinct species, endemic to Roraima State, northern Amazonia, Brazil. KEYWORDS: Fabaceae, Mimosoideae, embryo, post-seminal development, testa Relevância taxonômica da morfologia de sementes e plântulas em duas espécies amazônicas de Entada (Leguminosae) RESUMOEste trabalho apresenta um estudo morfológico comparativo para avaliar o valor taxonômico de caracteres de semente e plântula de Entada polystachya e E. simplicata (Leguminosae, Mimosoideae, Mimoseae). As sementes de ambas as espécies foram coletadas de populações no Estado de Roraima, Brasil. Os resultados evidenciaram consistentes diferenças qualitativas e quantitativas entre estas espécies, com relação as suas sementes e plântulas. Linhas de fratura na testa, impressão do funículo, caracteres da lente, forma e comprimento da radícula e comprimento dos lobos dos cotilédones, grupo morfológico de plântula, número de pinas no primeiro nó eofilar e comprimento do hipocótilo permitem uma separação entre E. polystachya e E. simplicata, providenciando apoio a um recente reconhecimento do último táxon como uma espécie distinta, endêmica no Estado de Roraima, Norte da Amazônia, Brasil. Taxonomic relevance of seed and seedling morphology in two Amazonian species of Entada (Leguminosae)

The large flood pulse of the Amazon basin is a principal driver of environmental heterogeneity with important implications for ecosystem function and the assembly of natural communities. Understanding species ecological response to the flood pulse is thus a key question with implications for theories of species coexistence, resource management, and conservation. Yet these remain largely undescribed for most species, and in particular for trees. The large flood pulse and high tree diversity of the Negro River floodplain makes it an ideal system to begin filling this knowledge gap. We merged historical hydrologic data with 41 forest inventories under variable flooding conditions distributed across the Negro River basin, comprising a total area of 34 ha, to (i) assess the importance of flood duration as a driver of compositional variation, (ii) model the response curve shapes of 111 of the most frequent tree species in function of flood duration, and (iii) derive their niche properties (optima and tolerance). We found that flood duration is a strong driver of compositional turnover, although the majority site-to-site variation in forest composition still remains unexplained. About 73% of species responded to the flood duration gradient, exhibiting a diversity of shapes, but most frequently skewed. About 29% of species were clearly favored by flood durations >120 days year–1, and 44% of species favored by shorter floods. The median niche breadth was 85 flood days year–1, corresponding to approximately 30% of the flood duration gradient. A significant subset of species (27%) did not respond to flooding, but rather exhibited wide tolerance to the flood gradient. The response models provided here offer valuable information regarding tree species differential capacity to grow, survive, and regenerate along an ecologically important gradient and are spatially valid for the Amazon Negro basin. These attributes make them an appealing tool with wide applicability for field and experimental studies in the region, as well as for vegetation monitoring and simulation models of floodplain forest change in the face of hydrologic alteration.

The evaluation of the post-germination phases of plants allows the recognition of transitional structures that support the relationships among taxa and their establishment. Together with fruit and seeds, seedlings and saplings provide useful characters for identifying many species. This study aimed to describe and characterize the morphology of the fruits, seeds, seedlings and saplings of Macrolobium acaciifolium, M. bifolium and M. pendulum, as well as to evaluate the ecological, taxonomic and phylogenetic value of the structures identified. In this work, the seeds were sown in plastic trays with sterilized sand and sawdust, without pre-germination treatment. The fruits of the three species are woody legumes, dehiscent fruit or indehiscent fruit. The seeds have seed coats with or without venation and variable embryos, with plumules differing among the three species; this trait can be helpful in distinguishing among the species studied. The seedlings are of the cryptocotylar-hypogeal-reserve or phanerocotylar-epigeal-reserve type. Macrolobium bifolium and M. pendulum are similar species, differing in only a few characters. These characters have taxonomic value and aid species identification. The characteristics of M. pendulum are described here for the first time.

ResumoEntada é um gênero pantropical de Leguminosae (Mimosoideae) AbstractEntada is a pantropical legume genus (Leguminosae, Mimosoideae) with 28 species. This paper presents a taxonomic survey of Entada in Roraima state, north Brazil. Three Entada taxa have been recognized in Roraima, treated here as separate species: E. polyphylla, E. polystachya and E. simplicata. An identification key, descriptions, illustrations, as well as information on geographic distribution, habitats and dispersion, are also provided. Both the endemism of E. simplicata and the first record of E. polyphylla make Roraima the only state where all species of Entada recorded in Brazil occur.