The impact of dams
The liana-to-tree ratio is tipped in favour of the woody vines when tropical forests are disturbed – for example, by fragmentation where continuous forest is split into smaller pieces for agriculture or other land uses – because lianas are well adapted for those environmental conditions.
Hydropower generation in Amazonia is another cause of fragmentation, with large swathes of forests left flooded when dams are closed, transforming former hilltops into islands.
It is known that forest islands lose biomass due to reduced habitat area, however, the new study reveals for the first time that a dam-induced landscape can result in lianas dominating the tree population, as witnessed in other disturbed tropical forest systems.
Islands missing from impact assessments
Dr Jones’ team conducted field surveys of lianas and trees, surveying a total of 89 forest plots across 36 islands of different sizes and in continuous forests surrounding the reservoir.
The scientists – including experts from the University of East Anglia in Norwich, Universidade Estadual de Santa Cruz in Brazil and the Smithsonian Tropical Research Institute in Panama – found that a greater number of lianas are starting to grow than trees in the most disturbed islands.
In addition, they discovered that liana communities remain compositionally intact regardless of whether they are in a forest or on a disturbed island. This robustness in a dam-induced habitat is particularly significant as trees rapidly degrade in such an environment, they said.
‘At present, islands are not included in environmental impact assessments, which causes a significant underestimation of the negative impacts of tropical dams’
‘Given that Brazil alone has plans for several new mega-dams, which will flood vast areas of highly diverse tropical forests, it is important that the total area of islands should be included in calculations considering the habitat impacted by dam creation.’
DR ISABEL JONES
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