Wildlife loss in tropical forests is bad news — and not just for animals

Western gorilla (Gorilla gorilla) from TEAM's site in Nouabale-Ndoki National Park, Republic of Congo.

A camera-trap image of a western gorilla in Nouabale-Ndoki National Park, Republic of Congo. (Photo courtesy of the TEAM Network and Wildlife Conservation Society)

I had drinks with an old college friend last week. As we reminisced and I caught him up on my job leading the Tropical Ecology Assessment & Monitoring (TEAM) Network, he stopped me mid-sentence.

“Don’t get me wrong — I love animals, and camera trapping is cool,” he said. “But why spend so much time and energy keeping track of species halfway around the world? Why does it matter if tapirs in Ecuador or chimps in Uganda are declining? Why should I care?”

This wasn’t the first time I’d been asked these kinds of questions while working with TEAM, which uses camera-trap data to calculate trends in mammal and bird populations in tropical forests on three continents.

In the past, I would respond somewhat vaguely, saying “Wildlife provides key ecosystem services,” or “Animals are a good way to measure the health of a forest.” Though true, these answers were unsatisfying, even to me. It is like answering “Why do you need your liver?” with “Because it keeps your body going.” True, but not compelling or especially useful.

This time I had a better answer, backed by science.

The idea

In 2014, Anand Osuri, a Ph.D. student at the National Centre for Biological Sciences in Bangalore, India, emailed saying he had come across our TEAM camera-trap data and it sparked an idea for a project.  What if we could measure how animals living in tropical forests impact the amount of carbon that the trees in those forests are able to store?

Osuri and collaborators came up with an ingenious computer simulation to explore this question. First, he took tree plot data collected by TEAM and others, and calculated how much carbon is stored in each plot. Within the computer program, he then “removed” from these plots tree species that depend on animals to disperse their seeds. This shows us what would happen in the forest if the animals were not there.

Next, Osuri replaced these trees with a random selection of tree species from the forest. Finally, he re-calculated the amount of carbon stored in the new forest and compared it to the original amount. He repeated this process many times for each plot to ensure that the results were not biased by any one simulation.


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The results

What happened was amazing. The simulation found that when all animal-dispersed trees were replaced by other species, carbon storage decreased in most plots — a loss of up to 12% in Cameroon, 6% in India and Peru and 3% in Panama. There were two exceptions: In Indonesia and Australia, carbon storage remained stable or slightly increased. These forests have fewer trees dispersed by animals (< 75%) compared to forests in Africa and Latin America (87%) and South Asia (90%). But on average, carbon storage decreased by 4%, which is roughly equivalent to the deforestation in the Amazon between 2000 and 2013.

This is big news. We already knew that the clearing and burning of tropical forests contributes 11% of global greenhouse gas emissions. Now we’re seeing that carbon emissions that fuel climate change can occur even if no trees are cut down, simply due to the disappearance of its animal inhabitants.

Inside Science: Candid cameras in the forest 
In this interview, Conservation International’s Jorge Ahumada explains what camera traps are showing us about the health of forest protected areas, how animals are adapting to climate change and how they might even be able to predict earthquakes.


To figure out the economic consequences of this species loss, we took Osuri’s results a step further. Mahbubul Alam, research economist at Conservation International’s Moore Center for Science, estimated the potential loss in monetary value of carbon in each of these forests. He found that, as animals are “eliminated,” most forest plots lose $US 48–228 per hectare in carbon value, measured as the economic damage that would result from the emission of each additional ton of carbon. Alam cautions this is a conservative estimate that only takes into account one aspect of economic value; further analysis may reveal the full economic implications, such as reduction in timber value and decline in pollination services.

Explore the results yourself in the simulation below. Select a country and then move the lever underneath to simulate the removal of wildlife from the forest. You can view two variables: 1) the amount of carbon stored in the “new” forest you’ve just created; and 2) the economic value of that stored carbon.

My new answer to “Why should I care?”

Losing wildlife from tropical forests is equivalent to emitting carbon into the atmosphere without cutting down a single tree. For example, losing wildlife in the Amazon over the next 40–50 years is equivalent to emitting 2.5 billion tons of carbon into the atmosphere or cutting down 26 million hectares (64 million acres) of forest, the size of the country of Gabon. The forest becomes less efficient at storing carbon from the atmosphere, hampering its ability to buffer us against climate change.

The consequences of climate change are already affecting all of us in some way, from higher food prices to more frequent droughts and floods. In order to solve this global problem, we must protect critical ecosystems — and the wildlife that keeps them going.

Jorge Ahumada is the executive director of the TEAM Network, a Conservation International-led coalition that also includes the Wildlife Conservation Society and the Smithsonian Tropical Research Institute.

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Further reading


  1. Pingback: Wildlife loss in tropical forests is bad news &...


    Hola JorgeA: Se me hace genial este tipo información-basada-en-la-evidencia. Es también la base actual para el campo médico. Leí hace poco que cambios muy significativos se observaron en alguna región casi destruida desde el punto de vista ecológico con la sola de introducción de lobos, antes desalojados, en dicho ambiente.

  3. Simon Jennings says

    Surely if you run a model in which you remove 90% of the indigenous tree species and create a forest in which the remaining 10% suddenly come to constitute the entire community, you are creating a depauperate forest of tree species which may formerly have been less dominant because they are poorly adapted to succeed as generalists in a forest landscape (which is why they were formerly present at a level of collective occurrence of only 10%), and for that reason will not do well if forced to perform as generalists, and their underperformance will be reflected in the rate at which they build biomass. That does not detract from the point that the dominant tree community is one that benefits from animal dispersal. However it woudl be more convincing if the analysis removed only those tree species where it was known for sure that loss of animal dispersal meant certain extinction. If it is true that the reproductive strategies of many tree species that benefit from animal dispersal are not entirely dependent on that mode of dispersal, then the results of this very interesting model (great idea!) might be somewhat compromised. Eg if a monkey or a hornbill stops transporting fruits around, do those fruits fall to the floor and germinate? This would change the spatial dynamics but might not result in the loss of that tree species from the forest community!

    1. Jorge says

      The simulation only removes animal-dispersed species (not any species). Researchers also perform “controls” where they removed similar numbers of trees but drawn at random from the community. This ensures that the carbon change seen is due to removal of animal-dispersed trees –not just any tree species (follow the link to the original paper for a more thorough explanation). To answer your question at the end, there is a large body of knowledge showing that for animal-dispersed tree species, seeds that fall under the tree have a significant lower chance of survival due to pathogens and predation compared to seeds that are dispersed.

  4. Brian de Castro says

    Interesting studies, and further proof that we are all interconnected and depend on each other for survival. It’s almost like the butterfly effect. Kill something in one part of the world, and it will have an effect on something on the opposite side of the globe, but sooner than we think. And for those who have little to no concern with what is happening in the far corners of the planet, you are part of the problem. We all share the planet together and must work together – all of us – to ensure its health for generations to come. Anything else is ignorant, selfish and foolish.

  5. Roger Harris says

    Good article. Pity it is marred by the title which perpetuates the myth that humans are not part of the Animal Kingdom, viz. “…bad news and not just for animals” when we are animals of course.

  6. David Rosenthal says

    Hi Jorge,
    Great commentary, like the paper too. I read the paper for our weekly discussion group and one question comes up about the paper and title in particular. The paper and your article title claim that the removal of seed dispersers will cause the loss of forest C. But this study does not actually simulate the loss of the seed dispersers, just the trees. I understand the theory but is there empirical evidence that the loss of the dispersers is, can or will change community structure in any or all of these forests?

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