Large fruitarian animals, including elephants, tapirs, monkeys and
hornbills help to control global warming, a new study has found.
Reason: These animals help many tropical forest trees to disperse
seeds. So not conserving these large animals could substantially
change carbon storage in tropical forests globally, thereby altering
their ability to regulate the world’s climate, according to scientists
from the National Centre for Biological Sciences (NCBS), Bengaluru.
“Scientists are only just beginning to understand the numerous ways in
which animals affect the carbon cycle of tropical forests, and the
consequences of declines or loss of these animals, also termed
defaunation, for terrestrial carbon storage,” said Anand M Osuri, a
member of Dr Mahesh Sankaran’s group at NCBS and the study’s lead
author.
The fieldwork
The team of researchers from NCBS, Nature Conservation Foundation
(NCF), Mysuru, University of Leeds and 12 other international academic
and conservation organisations examined how tree species that are
dispersed by large animals differ from tree species dispersed by other
modes (for example, wind or gravity) in their ability to store carbon.
They used a dataset of over 26,000 trees belonging to 2,500 species
from tropical forests in Asia, Africa, the Americas and Australia to
examine the effects of defaunation on aboveground carbon storage of
tropical forests globally. Using a simulation-based approach, they
created various ‘defaunation scenarios’, that is, different conditions
in which trees dependent on large animals for seed dispersal gradually
declined. Defaunation-driven changes in carbon storage were assessed.
Plants, during photosynthesis, intake carbon dioxide, convert it in
carbon and store it within. The researchers found that large-seeded
tree species, which depend on big animals for seed dispersal, grow to
greater sizes as adults and thus have higher carbon storage potential
than species with smaller seeds in tropical forests.
The results, published in Nature Communications, say that in South
Asia, Africa and the Americas, where majority of tree species are
dispersed by animals, losses of large seed dispersers can reduce
carbon storage by decreasing the volume of vegetation biomass. The
team says 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 two per cent, which is
roughly equivalent to 14 years’ worth of Amazonian deforestation.
Save those jumbos
“At present, an estimated 88 per cent of all tropical forests face the
threat of defaunation through the combined effects of hunting, habitat
fragmentation and selective logging, with animals that disperse
large-seeded tree species amongst the most vulnerable. Given that
tropical forests of the Americas, Africa and South Asia, which
together account for over 75 per cent of all forests within the biome
(large ecological areas), are primarily composed of animal-dispersed
tree species, our results suggest that defaunation could have marked
negative effects on aboveground carbon storage in tropical forests
overall,” say the authors.
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