Grey-cheeked mangabey (Lophocebus albigena) feeding on Ficus sansibarica
at Kibale National Park. © Alain Houle. from fsd2010.com
from mongabay.com
According to the first study of its kind in Africa, bushmeat hunting impacts African rainforests by wiping-out large mammals and birds—such as forest elephants, primates, and hornbills—that are critical for dispersing certain tree species. The study, published in Biotropica, found that heavy bushmeat hunting in the Central African Republic changes the structure of forest species by favoring small-seeded trees over large-seeded, leading to lower tree diversity of trees that have big seeds.
"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 dispersion), 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."
Due to a dearth in data, Vanthomme and colleagues did not know which animals spread which plants, but instead had to hypothesize likely ecological interactions.
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.
Yet if these findings stand the test of time, it means forest structure is being changed in ways hardly imagined a few decades ago.
"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."
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Reference: Vanthomme H, Belle B, Forget PM (2010). Bushmeat Hunting Alters Recruitment of Large-Seeded Plant Species in Central Africa. Biotropica. 42(6): 672–679. doi: 10.1111/j.1744-7429.2010.00630.x.
ABSTRACT
We investigated the effect of local hunting on plant recruitment at the community level in the Ngotto Forest, Central African Republic. It is the first study of this kind in the afrotropics. To compare our results with previous studies conducted in the neotropics, we used the protocol proposed byNuñez-Iturri and Howe. We compared animal relative abundances and seed length, density and diversity of seedlings at two sites with contrasting anthropogenic pressures: one with low hunting pressure (LH) and one with high hunting pressure (HH). Furthermore, we investigated how density and diversity of recruitment vary with seed length in the two sites. Both sites exhibit similar soil, climate and tree species composition, and have never been logged. Large mammals (frugivores and herbivores) were extirpated from HH and relative abundance of medium-sized frugivores drastically decreased in HH compared with LH. In HH, diversity of seedlings was reduced compared with LH, especially for large-seeded plant species dispersed by large game mammals. The approach used in this study shows promising perspectives to investigate the effects of human disturbances on the regeneration of tropical forests. Furthermore, in the afrotropical context of a lack of data on plant–animal ecological relationships, seed length appears to be a good predictor of the strength of the deficit of plant recruitment due to large mammal extirpation because of hunting. Thus, more efforts are needed to study the ecological roles of large-seeded plants in order to better understand the effects of their disappearance on tropical forest resilience.
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