Study says large animals important for carbon storage in tropical forests

Friday 29 April 2016

Global decline in the population of several wild animal species is among the most widespread drivers of Earth’s biodiversity crisis

Researchers have found that big animals leave an impact on the carbon storage potential of tropical forests around the world and this is determined by their seed dispersal.

Researchers from the Bangalore-based National Centre for Biological Sciences (NCBS), the Nature Conservation Foundation in Mysore, the University of Leeds, UK, and 12 other international academic and conservation organisations were involved in the study. It has been published in the journal, Nature Communications, with Anand M Osuri as the lead author.

The study says that the global decline in the population of several wild animal species in the present era, termed as “Anthropocene Defaunation”, is among the most widespread drivers of Earth’s current biodiversity crisis.

Previous research indicates that defaunation can significantly alter the composition of tree communities due to changes in the seed dispersal process.

It has been observed that the abundance of tree species can be reduced by 60 per cent due to the decline of large vertebrate frugivores, including the large-seeded tree species of the tropical forests which are dependent on such animals for seed dispersal.

Vertebrate frugivores are fruit-eating animals, large mammalian and bird species. Mammalian species include primates such as orangutans, various species of macaques, bats (generally called fruit bats), elephants and bird species like hornbills, barbets and robins. Elephants are the largest frugivores on earth.

Large-seeded trees in the tropical forests contribute to form a huge “carbon sink” which plays an important role in regulating the atmospheric carbon dioxide concentration.

“Losses of large-seeded trees could substantially change carbon storage in tropical forests around the world, thereby altering their ability to regulate our world’s climate”, the NCBS reported.

It is important to understand that when it comes to carbon storage potential, not all tree species are the same. Large-seeded trees have higher carbon storage potential than small-seeded trees as the former attain bigger size as adults and are capable of storing more carbon.

Medium and large-sized vertebrate species such as primates, elephants and tapirs are important for maintaining the carbon storage potential of tropical forests around the world.

Accoridng to M Osuri, scientists are in the initial phase of the world-wide research where they are just beginning to understand the multiple ways through which seed-dispersing animals affect the carbon cycle of tropical forests and the impacts of defaunation on terrestrial carbon storage.

Defaunation and carbon storage

To understand the link between defaunation and carbon storage in tropical forests, researchers adopted a simulation-based approach in which various “defaunation scenarios” were created.

These scenarios were based on different conditions under which trees with modes of seed dispersal such as small animals, or abiotic factors like wind and gravity, replaced trees dependent on large animals for seed dispersal due to the decline in the number of megafauna.

The trees in the original and defaunated forest were then compared with respect to their sizes and wood densities to assess the effect of defuantion on carbon storage.

As NCBS reported, the results of the study suggest that “in Africa, the Americas and South Asia, where the majority of tree species are dispersed by animals, losses of large-seed dispersers can reduce carbon storage by decreasing the volume of vegetation biomass”.

“In some regions, especially the Americas, carbon losses may be heightened further due to declines of tree species with high wood density following losses of large seed dispersers. If 50 per cent of all trees dispersed by large animals were replaced over time by trees with other modes of seed dispersal, carbon storage in these forests would be reduced by 2 per cent. This is roughly equivalent to 14 years’ worth of Amazonian deforestation,” the study says.

NCBS also made an important inference from the study to provide new insights into policies like REDD+, which primarily focuses on reducing carbon loss by protecting tropical forests from deforestation and logging.

REDD+ is a United Nations programme aimed at reducing emissions from deforestation and forest degradation.

The study highlights the importance of conserving large wild animals in the tropical forests as part of forest protection strategy for storing carbon and reducing emissions. This will ultimately help us to mitigate climate change.

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