Researchers from Unicamp and Embrapa participate in a study that indicates which animal contributes to the maintenance of trees with more biomass
The African forest elephant (Loxodonta cyclotis) is known for his ability to act as a “gardener”. As it travels through the African tropical forests, the animal spreads a vast number of fruit seeds, from a great diversity of trees on which it feeds. In this way, it helps the germination of more than a hundred species of trees, which also provide food or serve as shelter for primates, birds and insects.
An international study, with the participation of researchers from the State University of Campinas (Unicamp) and Embrapa Informática Agropecuária, concluded that the role played by the African forest elephant in African tropical forests, however, goes far beyond seed dispersing. The researchers found that the animal – threatened with extinction – promotes changes in the structure of the forest and contributes to increasing carbon storage.
During the walk, in addition to feeding, the elephant tramples, runs over or scratches itself on trees located close to the trails it preferably uses to cross the forest. Thinning these trees reduces their density over time.
Reducing the density of trees alleviates competition for water, light and space between them and favors the emergence of larger trees, with greater diameter and wood density and, consequently, more carbon stored in biomass. This change in the structure of African tropical forests and the composition of tree species influenced by the animal also increases, in the long term, the balance of aboveground biomass, the study found.
Result of a project supported by FAPESP, the work was published in the journal Nature Geoscience.
“We observed that the presence of elephants at a density of 0,5 to 1 animal per square kilometer increases above-ground biomass by 26 to 60 tons per hectare of the forest,” said Simone Aparecida Vieira, researcher at the Center for Environmental Studies and Research. (Nepam) from Unicamp and one of the authors of the study, to Agência FAPESP.
The researcher was part of the organizing committee of the São Paulo School of Advanced Science in Scenarios and Modeling in Biodiversity and Ecosystem Services, held from July 1st to 14th in São Pedro, in the interior of São Paulo. With support from FAPESP, through the São Paulo School of Advanced Science (ESPCA) program, the event brought together 87 students from 20 countries.
Also participating in the study were Marcos Longo, a postdoctoral fellow at the Jet Propulsion Laboratory at NASA, the United States space agency, who did his postdoctoral work at Embrapa Informática Agropecuária with a scholarship from FAPESP, and Marcos Augusto da Silva Scaranello, also a postdoctoral fellow at Embrapa Informática Agropecuária with a FAPESP scholarship, and Marcos Augusto da Silva Scaranello, also PhD student at the same institution. Scaranello completed his doctorate at IB-Unicamp also with a scholarship from FAPESP.
According to the study authors, it was already known that megaherbivores, such as elephants, can have an important impact on ecosystems and biogeochemical cycles by consuming biomass, transporting nutrients and altering plant mortality. The influence of elephants on the structure, productivity and carbon stocks of Africa's tropical forests, however, remained largely unknown.
“The tropical forests of Central Africa have larger carbon stocks than those of the Amazon Rainforest, although they are in similar climatic and soil conditions,” said Vieira.
Trees in Central African forests have a lower stem density and greater diameter and average biomass above ground compared to those in the Amazon, explained the researcher.
“The presence of elephants in the tropical forests of Central Africa may have contributed to explaining these differences in relation to the Amazon over long periods of time,” said Vieira.
In order to test this hypothesis, the researchers used a computational model of ecosystem dynamics (ED2 model). The model explicitly tracks the dynamics of fine-scale ecosystem structure and function, simulating horizontal and vertical vegetation heterogeneity in long-term forest succession, plant competition for resources leading to mortality, as well as stochastic disturbance events that can influence the structure of the forest in the short, medium and long term, such as the presence of elephants.
The simulations were compared with inventory data from two forests in the Congo Basin: in one of them there is still the presence of elephants and, in another, the animals have been eradicated.
The results showed that the introduction of elephants causes a temporary effect of reduction in the concentration of biomass above the forest floor, on a scale of 125 to 250 years, due to the increase in mortality of small trees due to the animal's action. The increase and successive balance in the concentration of biomass above ground are reached between 250 and a thousand years after the introduction of animals.
“The results support the hypothesis that their presence may have shaped the structure of the tropical forests of Africa and that it probably played an important role in differentiating them from the tropical forests of the Amazon,” said Vieira.
Extinction of elephants
The researchers also simulated the effects of elephant extinction on the concentration of above-ground biomass across the entire Central African forest – 2,2 million square kilometers in size.
The results indicated that the loss of the animal would result in a 7% decrease in above-ground biomass and up to 3 billion tons of carbon.
Elephant conservation can reverse this trend of declining carbon storage services estimated at US$43 billion, researchers point out.
"Our simulations suggest that if elephant loss continues unabated, Central Africa's forests could release several years' worth of fossil fuel CO2 emissions from most countries, potentially accelerating climate change," said Fabio Berzaghi, a researcher at the Laboratory of Environmental and Climate Sciences (CEA), from France, and main author of the study, in a statement from the institution.
“The loss of this animal can have a drastic impact, both locally and globally,” he said.
The population of forest elephants has fallen dramatically since the colonization of West Africa by Europeans, when the animals began to be hunted for ivory. Today, elephant species have dwindled to less than 10% of their original numbers.
THE ARTICLE
The article Carbon stocks in central African forests enhanced by elephant disturbance (doi 10.1038/s41561-019-0395-6), by Fabio Berzaghi, Marcos Longo, Philippe Ciais, Stephen Blake, François Bretagnolle, Simone Vieira, Marcos Scaranello, Giuseppe Scarascia- Mugnozza and Christopher E. Doughty, can be read by subscribers to the journal Nature Geoscience
