- In the past three decades, poaching has decimated Africa’s now-critically endangered forest elephants, and as a result, their vital role as seed dispersers of many forest plants has been disrupted.
- A new study from Cameroon provides the first direct evidence that without forest elephants, there are fewer ebony saplings; on average, as few as 68%, in Central African rainforests.
- Researchers found that seeds pooped out in elephant dung have a better chance of surviving and sprouting as they are protected from hungry rodents and other herbivores that chew and destroy the seeds.
- The findings show that losing key ecosystem engineers and seed dispersers has far-reaching ecological and economic impacts, potentially altering entire ecosystems.
In 2017, when Vincent Deblauwe joined the Cameroon-based Congo Basin Institute (CBI) to study African ebony (Diospyros crassiflora) — economically valuable pitch-black, dense wood — the Indigenous Baka people accompanied him on his field trips. As they sat around campfires and trekked through the rainforests, Deblauwe tapped into their knowledge of flora and fauna, especially about ebony trees and their dispersal. They all told him that one animal was responsible for the ebony tree’s future survival: the forest elephant (Loxodonta cyclotis).
Deblauwe observed that in forest patches without elephants, young ebony saplings were few and far between. Over the last three decades, relentless poaching, fueled by the insatiable demand for ivory in China and Southeast Asia, has plunged African forest elephant numbers by a whopping 86%, pushing them perilously close to extinction. However, the long-term impacts of this mass slaughter on the region’s trees remained largely unknown.
In the years that followed, Deblauwe and his colleagues braided the Baka people’s knowledge about ebony and elephants with spatial, genetic and experimental data on ebony trees, providing the first convincing evidence of a mutualistic relationship between the two species, now published in a new study in the journal Science Advances.
The researchers teased out why elephants play such a vital role in maintaining ebony trees in the forests. When elephants eat the large, pulpy ebony fruits and excrete the seeds, their dung protects those seeds from rodents and other animals that would otherwise eat and destroy them.
“Our findings show that forest elephants preferentially consume ebony fruits and play a crucial role in seed dispersal,” said Thomas Smith, one of the study’s authors and a founder and director of CBI.
This relationship is so close-knit that when poaching lowers elephant populations or removes them from forests altogether, ebony trees also dwindle. Deblauwe and his team documented a 68% drop in ebony saplings in areas lacking its key disperser. The sprouting and growth of new ebony trees virtually collapsed.
Ebony trees are already vulnerable, as the trees are felled for timber and forests leveled to make way for expanding human populations. This smooth, hard, black wood is also highly sought after for musical instruments and other high-end products.
This study “does such a thorough job of linking this sort of mechanistic relationship with really clearly demonstrable data of declines of ebony with elephant declines, said elephant ecologist Stephen Blake at Saint Louis University, U.S., who was not involved in the research. “Nobody’s quite nailed that before.”
The findings “underscore the broader consequences of forest elephant declines for many other rainforest trees that rely on large vertebrates for seed dispersal,” Smith said. It adds to a growing body of research showing that up to 90% of tree species have evolved relationships with animals to reproduce and spread.
Elephants: Landscape architects of the forest
As gardeners of the forest, elephants change the structure and composition of forests by trampling, bulldozing and digging up plants and trees. They favor slow-growing trees that have high wood density. The higher the density, the more carbon trees store, thereby increasing the carbon stocks of forests. As seed dispersers, elephants carry seeds of dense, slow-growing trees — like ebony — far, far away, over longer distances than any other animal.
“Elephants are an intrinsic, incredibly important part of the ecosystem,” Blake said, and their decline in recent years is worrying for the future of rainforests. “Their ecosystem processes are vanishing with them,” he said, adding that ”the loss of gardeners from the garden means that the weeds take over.”
During the 19th century, forest elephants occupied the entire Congo Basin, but today, they are a critically endangered species with populations restricted to fragmented forest patches. In just a decade, from 2002-11, about 62% have vanished, and their range has shrunk by nearly 30%. Today, forest elephants overlap with only one-third of the ebony tree’s historical range.
Ivory and ebony, once lived in perfect harmony
For their study, the researchers sampled ebony trees in four unlogged forest patches in and around the Dja Faunal Reserve, a protected area in Cameroon. Two sites within the protected area had elephants — and low levels of poaching. The other two sites were outside the reserve, where poaching has nearly extirpated most animals, including elephants.
At each site, the team collected data on the diameter of ebony trees (to determine age), spatial and genetic distribution of saplings, and conducted experiments on how well seeds germinated with and without elephants and their protective dung.
The study correlated declines in elephant numbers with fewer young ebony trees. In areas where elephants were present, almost half of all ebony trees were young saplings, compared with just 15.1% in areas without the pachyderms. Seed “immigration” — the distance seeds dispersed from the mother tree — was five times higher in areas where hunting pressure was low, compared with areas where poaching was rampant.
Genetic diversity and survival of ebony trees were also affected in the absence of elephants. Since these gentle giants deposit the seeds far away from the parent tree, it reduces the chances of saplings clumping close to each other, competing for sunlight under the crown of their mother tree and spreads ebony genes widely.
Low genetic diversity makes trees less resilient to environmental changes, including diseases and impacts of climate change. Though primates and other animals also disperse ebony seeds, the authors say they fall short of filling the elephants’ role.
The team proved that elephant dung played a key role in helping ebony seeds survive and grow. The dung protects seeds from being chewed up and destroyed by rodents such as Emin’s pouched rats (Cricetomys emini) and herbivores like yellow-backed duikers (Cephalophus silvicultor). The study found that naked seeds were 8.5 times more likely to be devoured than those encased within elephant dung. This loss due to predation, the researchers say, explains why ebony declines when elephant numbers decrease.
Seeds that drop to the forest floor within fruits also had low sprouting success: They rot before germinating. So it’s vital for elephants and other fruit-eating (but seed-sparing) animals, to chew up the pulp and excrete the seeds.
Deblauwe said the findings highlight the indirect benefit of conserving charismatic species like elephants that attract substantial funding. “Here we show that when you protect elephants, you are also protecting trees that are important for both the ecosystem and people over the long, long-term.”
Ebony — the first wood to be commercially exploited from Africa that remains economically valuable — is so slow-growing that it takes more than a century to mature. Therefore, this tree can also act as an indicator of elephant numbers in the past, Deblauwe said. Ebony’s decline today is the result of elephant declines a few decades ago. “In 100 years, maybe we’ll discover the true damage that has been done to the forest today.”
The study underscores the interwoven nature of ecosystems and the long-term consequences of eliminating members of these communities. In this case, losing elephants impacts the diversity of rainforests, not just ebony. It also reiterates the need to stop elephant poaching — and build wildlife corridors between protected areas for elephants to move and disperse seeds so the forests remain biodiverse and resilient.
“We are really on the precipice of extinction of forest elephants and the extinction of those ecological processes that regenerate forests,” Smith said. “This is kind of code red. … We need to really act now to preserve forest elephants.”
African forest elephant feeding on ebony fruits in the rainforest of Lobéké National Park, Cameroon. Video courtesy of Vincent Deblauwe, IITA, CBI, UCLA.
Banner image: Critically endangered African forest elephants act as seed dispersers in the rainforest, taking the seeds far, far away from the mother plants. Image © markusgmeiner via iNaturalist (CC BY-NC).
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Citations:
Deblauwe, V., Luskin, M.S., Assola, S.D., Hardy, O.J….Jansen, S., (2025). Declines of ebony and ivory are inextricably linked in an African rainforest. Science Advances, 11(35), doi:10.1126/sciadv
Caughlin, T. T., Ferguson, J. M., Lichstein, J. W., Zuidema, P. A., Bunyavejchewin, S., & Levey, D. J. (2014). Loss of animal seed dispersal increases extinction risk in a tropical tree species due to pervasive negative density dependence across life stages. Proceedings of the Royal Society B Biological Sciences, 282(1798), 20142095. doi:10.1098/rspb.2014.2095
Berzaghi, F., Bretagnolle, F., Durand-Bessart, C., & Blake, S. (2023). Megaherbivores modify forest structure and increase carbon stocks through multiple pathways. Proceedings of the National Academy of Sciences, 120(5). doi:10.1073/pnas.2201832120
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