81% of tropical tree species need an animal to carry their seeds somewhere useful. When the large fruit-eaters go, the trees that depend on them thin out, and in many forests those are the big, dense, carbon-heavy ones. The research below is where that story is solid, and, just as importantly, where it is not.
What a forest elephant does to a rainforest, and what its loss costs.
ModelledBerzaghi F, Longo M, Ciais P, Blake S, Bretagnolle F, Vieira S, Scaranello M, Scarascia-Mugnozza G, Doughty CE · Nature Geoscience, 2019 · doi:10.1038/s41561-019-0395-6
Elephants thin out small stems as they move and feed, which leaves fewer trees competing for light and water and shifts the forest towards larger trees with denser wood. At the usual density of half an elephant to one elephant per square kilometre, that raises aboveground biomass by 26 to 60 tonnes per hectare. Losing forest elephants entirely is estimated to cut aboveground biomass across central African rainforest by 7%.
What this does not show
An Ecosystem Demography model checked against forest inventory data, not a measurement of elephants being removed. The same shift lowers the forest's net primary productivity, because denser wood grows more slowly, so the gain is in stock rather than in growth rate. The paper carries a published author correction (doi:10.1038/s41561-019-0487-3), which is worth reading alongside it.
Where it applies: Central African lowland rainforest.
Tapirs, and the surprising place they do their most useful work.
MeasuredPaolucci LN, Pereira RL, Rattis L, Silvério DV, Marques NCS, Macedo MN, Brando PM · Biotropica, 2019 · doi:10.1111/btp.12627
Tapirs dispersed about 9,800 seeds per hectare a year in forest damaged by fire and fragmentation, against about 2,950 per hectare a year in undisturbed forest. That is roughly three times more work in the places that need it most, apparently because tapirs prefer ground where resprouting growth gives them something to eat. The team identified close to 130,000 seeds from 24 species out of tapir dung.
What this does not show
One region of the Brazilian Amazon, so the ratio should not be assumed to hold elsewhere. It measures seeds delivered, which is not the same as seedlings that survive, and the paper does not follow them to established trees. The link to carbon is an inference from those seeds being large-seeded species that become large trees, not something this study measured.
Where it applies: Mato Grosso, Brazilian Amazon.
Rewilding as a climate measure, and the size of the claim being made for it.
ModelledSchmitz OJ, Sylvén M, Atwood TB, Bakker ES, Berzaghi F, Brodie JF, Cromsigt JPGM, Davies AB, Leroux SJ, Schepers FJ, Smith FA, Stark S, Svenning J-C, Tilker A, Ylänne H · Nature Climate Change, 2023 · doi:10.1038/s41558-023-01631-6
Restoring nine animal groups — African forest elephants, American bison, fish, grey wolves, musk oxen, sea otters, sharks, whales and wildebeest — is estimated to add 6.41 GtCO₂ of negative emissions a year. The authors set that against a natural climate solutions target of 10 GtCO₂ a year, which it would meet 64% of.
What this does not show
The authors say plainly that some of this is ALREADY counted inside existing natural climate solutions that protect these species' habitats, so it cannot simply be added to them. Press coverage of this paper often reports the figure against the 6.5 GtCO₂ a year implied by the 500 Gt by 2100 target, which makes it look like 95% rather than 64% and drops the double-counting caveat entirely. It is a synthesis of modelled estimates, not a measurement.
Where it applies: Global, across nine species groups on land and at sea.
A single rewilding project, and why we do not put its number in a headline.
ModelledSchmitz OJ and colleagues, Yale School of the Environment, with the Global Rewilding Alliance · Reported May 2024; analysis not peer reviewed at the time of writing, 2024
A herd of about 170 European bison grazing roughly 20 square miles is estimated to help capture an additional 54,000 tonnes of carbon a year, around ten times what the same ground was drawing down before the bison were returned.
What this does not show
Not peer reviewed. It is the output of a model rather than a field measurement, and press accounts of it disagree with one another on the car-equivalence figure, which is a fair warning about how far the number has travelled from its source. It describes a whole ecosystem's response, so dividing it by 170 to get a figure per bison is not something the work supports, and we do not do it.
Where it applies: Țarcu Mountains, Southern Carpathians, Romania.
Seed-dispersing animals and the rate at which tropical forest regrows.
Measured data, modelled resultFricke EC, Cook-Patton SC, Harvey CF, Terrer C · Proceedings of the National Academy of Sciences, 2025 · doi:10.1073/pnas.2500951122
Across 3,026 tropical regrowth plots, areas with the least disruption to seed dispersal accumulated about four times as much carbon as those with the most. For a typical restoration site the loss averaged −1.8 Mg of carbon per hectare per year, a 57% reduction in regrowth potential. 81% of tropical tree species depend on animals to move their seeds.
What this does not show
The four-fold figure describes the RATE at which cleared land regrows, not the carbon a standing forest holds — the two are often confused. The authors note gaps in the resolution of animal biodiversity data, possible mismatches in space and time, and uneven monitoring coverage across the tropics. The analysis treats birds and mammals together and does not separate out primates.
Where it applies: Tropics globally, with the Amazon Basin, Congo Basin and Borneo examined closely.
Why losing large fruit-eating animals affects carbon in some forests and not others.
ModelledOsuri AM, Ratnam J, Varma V, Alvarez-Loayza P, Hurtado Astaiza J, Bradford M, Fletcher C, Ndoundou-Hockemba M, Jansen PA, Kenfack D, Marshall AR, Ramesh BR, Rovero F, Sankaran M · Nature Communications, 2016 · doi:10.1038/ncomms11351
Removing large-seeded animal-dispersed trees entirely cost 2–12% of aboveground carbon in African, American and South Asian forests, and 1–5% under a halved scenario. Southeast Asian and Australian forests showed little change or a marginal gain, within ±1%.
What this does not show
This is the source that stops a blanket claim. The effect depends on which tree species a forest happens to hold, so 'protecting frugivores protects carbon' is true in some regions and not others. The scenarios are simulations, the authors report insufficient data on how defaunated forests actually change over time, and soil and leaf-litter carbon are not covered at all.
Where it applies: Ten sites across Africa, the Americas, South Asia, Southeast Asia and Australia.
The scale of carbon change from losing large fruit-eaters in one measured forest.
ModelledChanthorn W, Hartig F, Brockelman WY, Srisang W, Nathalang A, Santon J · Scientific Reports, 2019 · doi:10.1038/s41598-019-46399-y
Simulating the complete loss of large-bodied frugivores reduced aboveground carbon by 2.4–3.0%. Carbon loss passed 1% once defaunation reached 40%.
What this does not show
A simulation built on one 30-hectare plot of 33,844 trees, assuming the community settles to a new equilibrium rather than modelling the transition. Species-level demographic data was missing, rodents may partly compensate by moving seeds, and the authors state considerable uncertainty about how surviving species compete.
Where it applies: Mo Singto plot, Khao Yai National Park, Thailand.
Primates and tapirs specifically, in Neotropical forests.
Review of other studiesBennett EL, Robinson JG · PLOS Biology, 2023 · doi:10.1371/journal.pbio.3002262
Summarising modelling work, losing large primates and tapirs is projected to cut aboveground tree biomass by 2.5–5.8% on average in the Neotropics, and by as much as 26.5–37.8% in the worst cases.
What this does not show
A Perspective piece, not primary research: it reports other people's models rather than new measurements. The authors note the picture is complicated by hunting also removing seed PREDATORS, which pushes the other way, and no direct measurement of primate-dispersed carbon is offered.
Where it applies: Tropical forests, drawing on the Brazilian Amazon, Central Africa and Thailand.