November 04, 2010
"When hunters remove big animals, they remove at the same time the ecological functions of the animals," lead author Hadrien Vanthomme, from the Museum National d'Histoire Naturelle in France, explained to mongabay.com. "To keep it simple, animals can have two opposite impacts on forest regeneration: they can favor it (mostly by carrying seeds away from the parent plants, phenomenon called dispersal), or they can oppose regeneration (by destroying seeds or young seedlings). So basically, we expect that if a guild of animals implied in seed dispersal of a plant is removed, the regeneration of this plant species will be compromised."
A forest elephant in Gabon. Forest elephants have been decimated by poaching as researchers are only beginning to uncover their role as a super seed disperser. Photo by: Rhett A. Butler.
According to co-author, Pierre-Michel Forget, given the diversity of such it's almost impossible "to know all the actors involved—we are simply not enough and an army of scientists would be needed for that, just as to describe the diversity on earth—and what are the ecological services these animals offer to plants".
However by analyzing two plots in the Ngotto Forest, one with little hunting and the other with high hunting, they were able to paint a broad picture of the impact of bushmeat hunting on forests in the region, a "net effect" as Vanthomme puts it.
The study found that a number of key trees—the African star apple Chrysophyllum africanum, a species of cola nut tree Cola acuminate, and the Carapa procera, a species of mahogany—were all depleted in the high hunting site, most likely due to the lack of necessary seed dispersers. Each of these trees produces large seeds that probably require big mammals and birds to disperse successfully.
"Our results show a significant reduction of regeneration diversity in the hunted site compared to the less hunted site, and that this reduction also concern mainly animal-dispersed and large-seeded plant species," says Vanthomme.
Dr. Forget adds that the study's findings are buoyed by similar studies in South America that show that trees which hold similar ecological niches also vanish when hunting is high. However, since the study broke new ground, more research is needed to confirm the results and build a more complete picture of how hunting is changing forests, according to the authors.
"Duplicating this kind of study across Africa and other tropical forest will make it possible to compare the situation across space and better target the questions that need to be answered regionally. It will also be possible to choose appropriate plant species to further test hypotheses and produce data that could be used in ecological models to predict the future diversity of tropical rain forest plant species," says Vanthomme.
The red river hog, this one photographed in the Bronx Zoo, is a common target for bushmeat hunters, as well as being a seed disperser. Photo by: Rhett A. Butler.
"It would mean that hunting, on the long term, may affect the general balance of plant species in forests," says Vanthomme. "Consequences of this phenomenon are absolutely unpredictable, especially when associated to other disturbance like logging, fragmentation, or climate changes… One thing is sure: forest will never be the same."
New studies on seed dispersal in African tropical forests are already moving ahead according to Forget.
"In Rwanda, we are studying what happens when elephant disappeared and do not disperse seeds anymore, and whether rodents might compensate for the lack of dispersal of large seeds," he says. To date, he says results show rodents may in make-up for the absence of elephants in dispersing certain seeds. But, they do not spread seeds nearly as far as elephants, affecting tree species' "distribution and density".
While, seed dispersal studies have become almost common in South America and Southeast Asia, Vanthomme and Forget say that studies in Africa have taken time to get off the ground in part due to a lack of field stations and infrastructure in tropical Africa for researchers.
"It is crucial to develop and support field stations in Central Africa if we want to know more about how human activities impact the ecology and diversity of the rainforest. African scientists, for instance, have many difficulties to study their own forest due to the lack of infrastructure, and that is not fair," says Forget.
In addition, if researchers are to move forward in their understanding of the complex interactions between animals and plants in rainforests—knowledge that could prevent species and ecosystems from vanishing—Forget says that local education must be paramount.
"[We] need more researchers from tropical countries to describe the diversity and the essential relationships that exists linking plant to animals. And for that, we need to both educate a young generation of scientists, and to offer them the most favorable conditions for adequate learning and training to study rainforest ecology. That is the next challenge for educators, politicians and stakeholders if they don’t want the rainforest to disappear."
CITATION: Hadrien Vanthomme, Boris Belle, and Pierre-Michel Forget. Bushmeat Hunting Alters Recruitment of Large-Seeded Plant Species in Central Africa. Biotropica. Volume 42, Issue 6, pages 672–679, November 2010. doi: 10.1111/j.1744-7429.2010.00630.x.
Why seed dispersers matter, an interview with Pierre-Michel Forget, chair of the FSD International Symposium
(03/07/2010) There are few areas of research in tropical biology more exciting and more important than seed dispersal. Seed dispersal—the process by which seeds are spread from parent trees to new sprouting ground—underpins the ecology of forests worldwide. In temperate forests, seeds are often spread by wind and water, though sometimes by animals such as squirrels and birds. But in the tropics the emphasis is far heavier on the latter, as Dr. Pierre-Michel Forget explains to mongabay.com. "[In rainforests] a majority of plants, trees, lianas, epiphytes, and herbs, are dispersed by fruit-eating animals. […] As seed size varies from tiny seeds less than one millimetres to several centimetres in length or diameter, then, a variety of animals is required to disperse such a continuum and variety of seed size, the smaller being transported by ants and dung beetles, the larger swallowed by cassowary, tapir and elephant, for instance."
Vanishing forest elephants are the Congo's greatest cultivators
(04/09/2009) A new study finds that forest elephants may be responsible for planting more trees in the Congo than any other species or ghenus. Conducting a thorough survey of seed dispersal by forest elephants, Dr. Stephen Blake, formerly of the Wildlife Conservation Society (WCS) and now of the Mac Planck Institute for Ornithology, and his team found that forest elephants consume more than 96 species of plant seeds and can carry the seeds as far as 57 kilometers (35 miles) from their parent tree. Forest elephants are a subspecies of the more-widely known African elephant of the continent's great savannas, differing in many ways from their savanna-relations, including in their diet.
Hunting across Southeast Asia weakens forests' survival, An interview with Richard Corlett
(11/08/2009) A large flying fox eats a fruit ingesting its seeds. Flying over the tropical forests it eventually deposits the seeds at the base of another tree far from the first. One of these seeds takes root, sprouts, and in thirty years time a new tree waits for another flying fox to spread its speed. In the Southeast Asian tropics an astounding 80 percent of seeds are spread not by wind, but by animals: birds, bats, rodents, even elephants. But in a region where animals of all shapes and sizes are being wiped out by uncontrolled hunting and poaching—what will the forests of the future look like? This is the question that has long occupied Richard Corlett, professor of biological science at the National University of Singapore.
Long-distance seed dispersal and hunting, an interview with Kimberly Holbrook
(05/24/2010) Scientists are just beginning to uncover the complex relationship between healthy biodiverse tropical forests and seed dispersers—species that spread seeds from a parent tree to other parts of the forest including birds, rodents, primates, and even elephants. By its very nature this relationship consists of an incredibly high number of variables: how abundant are seed dispersers, which animals spread seeds the furthest, what species spread which seeds, how are human impacts like hunting and deforestation impacting successful dispersal, as well as many others. Dr. Kimberly Holbrook has begun to answer some of these questions.
How hornbills keep Asian rainforests healthy and diverse, an interview with Shumpei Kitamura
(04/26/2010) Hornbills are one of Asia's most attractive birds. Large, colorful, and easier to spot than most other birds, hornbills have become iconic animals in the tropical forests of Asia. Yet, most people probably don't realize just how important hornbills are to the tropical forests they inhabit: as fruit-eaters, hornbills play a key role in dispersing the seeds of tropical trees, thereby keeping forests healthy and diverse. Yet, according to tropical ecologist and hornbill-expert Shumpei Kitamura, these beautiful forest engineers are threatened by everything from forest loss to hunting to the pet trade.
Seed dispersal in the face of climate change, an interview with Arndt Hampe
(04/05/2010) Without seed dispersal plants could not survive. Seed dispersal, i.e. birds spreading seeds or wind carrying seeds, means the mechanism by which a seed is moved from its parent tree to a new area; if fortunate the seed will sprout in its new resting place, produce a plant which will eventually seed, and the process will begin anew. But in the face of vast human changes—including deforestation, urbanization, agriculture, and pasture lands, as well as the rising specter of climate change, researchers wonder how plants will survive, let alone thrive, in the future?