Research from the University of East Anglia in the UK centred on the Balbina Dam in Brazil has suggested that the structure has had a major impact on tropical rainforest biodiversity.
Published in PLOS ONE, the research - 'Widespread forest vertebrate extinctions induced by a mega hydroelectric dam in lowland Amazonia' - indicates a loss of mammals, birds and tortoises from the vast majority of islands formed by the creation of the vast Balbina Lake, one of the world's largest hydroelectric reservoirs.
The research team says it carried out intensive biodiversity surveys over two years on 37 islands isolated by the hydroelectric reservoir and three neighbouring continuous forest areas. They also surveyed land and tree dwelling vertebrates at these 40 forest sites.
Further research focused on plants and used high-resolution satellite images to better understand the level of forest degradation on the islands.
According to the researchers, the study shows clear evidence of widespread loss of animals on forest islands following 26 years of isolation, even under the best-case protection scenario ensured by the largest biological reserve in Brazil.
Large vertebrates including mammals, large gamebirds and tortoises aapeared to have disappeared from most islands formed by the creation of the Balbina Lake.
Of the 3,546 islands created, only 25 are now likely to harbour at least four fifths of all 35 target species surveyed in the study, says the researchers, adding that island size was the most important factor predicting the number of forest vertebrate species retained.
Dr Benchimol said: "We found that only a few islands larger than 475 hectares still contained a diverse community of animal and bird species, which corresponds to only 0.7 per cent of all islands in the reservoir," commented Lead author Dr Maíra Benchimol. "In addition to the effects of area reduction, most small islands succumbed to wind exposure and ephemeral fires that occurred during a severe El Niño drought in 1997-98. Post-burn islands retained even fewer wildlife species than islands of similar size that had not been affected by wildfires."
In another study published last month in Journal of Ecology the authors said that fires on these small islands have a knock-on effect for animal life, with extinction rates accelerated by the reduction of habitable forest.
Dr Benchimol added: "Different wildlife species respond differently depending on their lifestyles. Those that need small home ranges coped better with forest habitat loss caused by the dam. Nevertheless, the future demographic and genetic viability of small isolated populations in areas affected by major dams seems bleak, as few species are able to maintain gene flow by swimming long distances to reach other islands."
This research was funded by the Wildlife Conservation Society (WCS), the Natural Environment Research Council (NERC), The Rufford Small Grant Foundation, the Conservation Food and Health Foundation, Idea Wild, the Amazon Region Protected Areas (ARPA) programme, Amazonas Distribuidora de Energia S.A, Associação Comunidade Waimiri Atroari, and the Brazilian Ministry of Education.
While no other dams were considered in the study, the researchers claim that it adds evidence that forest biodiversity also pays a heavy price when large dams are built. What do you think? Share your thoughts with the editorial team via email: carrieannstocks@globaltrademedia.com.
