Why forest elephant extinction will make climate change much worse

Submitted by Naturenomics Team on Tue, 24/12/2019 - 13:34
A unlikely weapon against climate change

A unlikely weapon against climate change.
Image: REUTERS/Noor Khamis

Forest elephant extinction would exacerbate climate change. That’s according to a new study in Nature Geoscience which links feeding by elephants with an increase in the amount of carbon that forests are able to store.

The bad news is that African forest elephants – smaller and more vulnerable relatives of the better known African bush elephant – are fast going extinct. If we allow their ongoing extermination to continue, we will be also worsening climate change. The good news is that if we protect and conserve these elephants, we will simultaneously fight climate change.

Elephants are fascinating animals, and I have studied them for more than 15 years. They are intelligent, sentient, and highly social. But their single most remarkable feature is their size. Evolutionarily, elephants gambled on becoming massive enough to deter predators like lions and tigers.

In exchange, they became slaves to their appetite. Elephants need huge amounts of food everyday, something like 5-10% of their body mass. A typical three-tonne female could eat 200 kg of plant material in one day. Her family may need to consume more than a tonne of food per day.

It is not easy to find so much food, especially in tropical rain forests, where plants have high concentrations of chemical defences (toxins) to avoid being eaten. Elephants spend most of their life eating and looking for food. We can think of them as “eating machines”. African forest elephants are particularly fond of saplings, young trees, and the plants that first grow into newly opened gaps in the forest. These “early succession” plants are specialised in growing fast following a disturbance and they invest less in chemical defences. Early succession trees also have lower wood density than slow-growing late-succession tree species.

Elephant eating manners are also remarkable. They feed by breaking stems and branches, pulling down lianas, uprooting whole plants, stripping leaves off twigs, and so on. It is easy to notice their presence because of the mess they leave behind.

How elephant disturbance affects carbon stocks

The key novelty of the new study, by the ecologist Fabio Berzaghi and colleagues, is they include, for the first time, the effect of elephant feeding disturbances in a computer model that simulates demographic processes in forest ecosystems. They found that “elephant disturbance” – all that messy eating – results in forests having fewer, larger trees. Elephants filter out small early-succession (i.e. low wood density) trees, promoting the dominance of late-succession (high wood density) trees, which ultimately leads to long-term increases in the total biomass. Berzaghi and colleagues were able to validate their model predictions with data from real forest plots in the Congo Basin.

By promoting these larger, woodier trees, elephant feeding disturbances therefore mean the forest stores more carbon. These results have important and far reaching implications for elephant conservation and carbon policy. The authors estimate that the disappearance of African forest elephants would result in a loss of as much as 7% of the carbon stocks in Central African forests, which they valued at around US$43 billion, based on a conservative carbon stock price. In short, forest elephants are our allies in the fight against climate change and their existence saves us tens of billions of dollars in climate responses.

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