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.
Extreme climatic events and anthropic disturbances affect the hydrological regime of Amazonian rivers and connected floodplain forests. This study aims to investigate the impacts of the Balbina hydroelectric power plant on the floodplain forests of the Uatumã River, in the Central Amazon. For this, tree age and diameter increment from the most abundant tree species of three different topographic levels were obtained and analyzed in the affected area downstream of the Balbina dam (Uatumã River) and compared to an undisturbed site (Abacate River, affluent) considering age structure and mean diameter increments between the topographic levels and the two systems. The occurrence of old trees is much lower at the disturbed site compared to the undisturbed system. Especially at the middle topography of the Uatumã site, we observed tree species with high mean diameter increment indicating a strong disturbance. We suggest that the disturbances may be associated with extreme hydro‐climatic events, such as extreme droughts that occurred during the El Niño years 1925/26 and 1982/83 and that these events may increase vulnerability of igapó floodplains to wildfires. Abstract in Portuguese is available with online material.
RESUMOO Índice de Área Foliar (IAF) é determinante nos processos de trocas de massa e energia nos ecossistemas, sendo fundamental para o entendimento das mudanças no clima regional e na dinâmica do ecossistema. O objetivo deste trabalho foi analisar, por meio da geoestatística, a variabilidade e dependência espacial dos valores de índice de área foliar (IAF) em áreas naturais de campo 'baixo', campo 'alto' e floresta de transição no Sul do Amazonas. Os valores de IAF foram determinados numa malha regular com 33 pontos para cada área estudada, e a aquisição dos dados foi feita pelo analisador de dossel LAI-2000, que permite se calcular a estrutura da vegetação com base na radiação que penetra na copa das árvores. Os valores médios do IAF variaram de acordo com a área estudada, com maiores valores na floresta (4,42 m²m -2 ), seguida pelo campo alto (2,03 m²m -2 ) e campo baixo (1,72 m²m -2 ). Em todas as áreas os valores de IAF mostraram dependência espacial com o uso da krigagem entre as amostras e apresentam distribuição espacial diferenciada em cada área estudada: o grau de dependência espacial foi moderado na floresta de transição e fraco para os campos naturais, sendo que no campo alto a distância limite em que os pontos estão correlacionados é de 35,3 m. No mapa de krigagem foi possível observar manchas com valores altos e baixos distribuídos de forma diferenciada entre as áreas estudadas.Palavras-chaves: amazônia, geoestatística, índice de área foliar, Krigagem. Variability of the Leaf Area Index in natural fields and transition forest in Southern Amazonas State, Brazil ABSTRACTThe Leaf Area Index (LAI) has strong influence on ecosystems' energy and mass exchange and is fundamental to the understanding of regional climate changes and ecosystem
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