The study, published in PLOS ONE journal, suggests that current estimates fail to consider the full impact of forest fragmentation.
The team studied lianas – long-stemmed woody vines, like those used by Tarzan – within the Balbina hydroelectric dam in Brazil.
Lianas compete with trees for resources such as water and light. In some areas, lianas outnumber trees - causing the growth of low biomass liana-dominated forests. This can lead to animal food sources changing or disappearing while also lessening the ability of the forest to uptake and store carbon – vital for maintaining the global carbon balance.
In areas where tropical forests have been split into smaller pieces, or fragmented, for agriculture or other land uses, lianas outnumber trees.
Hydropower generation in Amazonia is one cause of fragmentation with large swathes of forests left flooded when dams are closed, transforming former hilltops into islands.
The 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
Dr Jones said, “If lianas are being favored in this dam-induced landscape, then the biodiversity and carbon losses associated with tropical hydropower could be greater than expected. This is due to the potential increased loss of tree biomass, due to liana-tree competition, as lianas have lower biomass relative to trees.”
“Therefore, a shift towards liana-dominated forest on tropical reservoir islands may result in even more biodiversity and carbon losses for already controversial tropical dams.”
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 more lianas than trees are growing 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.
“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. Jones concluded.
The study, Woody lianas increase in dominance and maintain compositional integrity across an Amazonian dam-induced fragmented landscape, was funded in part through a research grant from the Carnegie Trust.
Photo: Island within the Balbina hydroelectric dam in Brazil
