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Roads affect biodiversity by increasing mortality rates, habitat loss, and natural landscape fragmentation. Poorly installed culverts can impound streams, changing the environmental conditions, and affecting aquatic communities. We evaluated the effects of road crossings on the taxonomic composition and functional structure of fish assemblages in lowland eastern Amazonian streams, Brazil. We tested the hypothesis that the presence of road-derived impoundments affects assemblage taxonomic and functional composition and structure. Two predictions were addressed: (1) Species and functional group composition will differ in impounded reaches in relation to lotic reaches; (2) Assemblages in downstream lotic reaches will be richer in species and functional groups in relation to upstream lotic and impoundment reaches. We sampled five streams crossed by roads presenting impoundment formation, conducted by visual census (day, dusk, and night) in 200 m line transects. Assemblage composition from lentic reaches was different from lotic reaches, and Shannon diversity from downstream reaches was different from upstream and impoundment, however, beta diversity partitioning between lotic reaches showed higher nestedness contribution, reinforcing the role of impoundment in limiting fish dispersal between lotic reaches. These results suggest that impoundments impose environmental and dispersal constraints to fish, affecting their longitudinal distribution in streams fragmented by roads. [ABSTRACT FROM AUTHOR]

Studies on plants communities over time are important to predict their reaction when faced with disturbance, and so, for conservation. This study aimed to evaluate the floristic composition, richness, diversity and tree community structure in an area of cerrado sensu stricto at Fazenda Água Limpa, Brasília, DF, over a period of 27 years. Continuous surveys were conducted in the area every three years on 19 permanent plots of 1,000 m2 (20 × 50 m); during this time four fires occurred at the site. Periods of fire did not contribute to significant changes in richness and diversity for the woody community studied. Instead, it contributed to floristic and structural stability of the community, since community abundance and density changed considerably after long periods of fire exclusion. Fire suppression for longer periods than those observed may lead to significant structural and floristic changes in the community. [ABSTRACT FROM AUTHOR]