- Fruit-eating bats play an important role in maintaining forest health by being seed dispersers. For decades, researchers have explored ways to harness this capacity as a reforestation tool.
- One method has been to use fruit-derived essential oils to attract bats to deforested sites, where their seed-loaded feces may help stimulate regrowth.
- A recently published study goes one step further by using chemical compounds derived from those oils to attract bats. This new way of making lures could prove less expensive, so cheaper to scale up. But before such reforestation tools are widely implemented, more research and evidence are required.
- Long-term testing is needed to show that bat lures, and the seed dispersal they bring, markedly aid regrowth — a complex process that can fail due to seed competition with grasses and seed predation. Some experts say planted tree patches are better attractants; others say combined methods may work best.
Attracting seed-dispersing bats to degraded landscapes and aiding in tropical forest restoration efforts has long been an alluring prospect for conservationists: potentially a cheaper, less labor-intensive technique than media-hyped plantings of millions of trees.
Researchers have experimented with a variety of seed disperser lures for decades, but a recent project in Costa Rica may show an efficient, less costly way forward. Researchers successfully utilized synthetic chemical compounds derived from the fruit of Piper plants to attract wild fruit-eating bats.
“To locate fruits in the dark, bats rely on their sense of smell. In our study, we used synthetic volatile molecules that mimic the scents of fruits preferred by fruit bats to attract them,” Mariana Gelambi, study lead author and Virginia Tech postdoctoral researcher, writes in an email.
The research team placed these synthetic bat lures at sites within the La Selva Biological Research Station. They then observed fruit-eating bats from the genus Carollia drawn to the scent and also noted a slight increase in the quantity of seeds dispersed.
This work builds on past research that tested the potential of essential oils collected from tropical fruits to attract seed dispersers. The chemical scents used in the Costa Rica experiment could cut the costs of extracting essential oils from fruit, making this new approach a possible candidate for large-scale future use, Gelambi says.
In the past, researchers have explored other ways of attracting seed dispersers to deforested areas, deploying artificial bird nests and roosts and making sounds to attract a variety of seed-dispersing species to employ them as tropical forest restorers.
“We are losing tropical forests at an alarming rate, which is a serious concern because these ecosystems are essential for supporting wildlife, purifying the air, storing carbon and providing countless other [ecological] services,” Gelambi says. “Our ultimate goal is to contribute to the development of an effective strategy that uses fruit bat attraction to support forest restoration efforts.”
The new study provides a good initial step by demonstrating the potential of these attraction methods in the field, says Lays Parolin, an ecologist at the Pontifical Catholic University of Paraná. Parolin has conducted studies using essential oils as lures in Brazil but primarily on bats in captivity.
“We have the theory that this can work, but there are still a lot of things we need to test in order make this bat attraction method more robust,” she says.
But do bat lures truly assist regrowth?
Proving that a natural or chemical attractant can lure bats or other seed-dispersing animals to a location is one thing. Determining whether or not that wildlife is sufficiently dispersing seeds to help regrow a forest is quite a different matter, requiring long-term observation.
Scientists already know that seed dispersers, including fruit-eating bats, play a vital role in maintaining forest health. As bats fly place to place in search of food, they release feces often loaded with seeds — providing a source of new life and some fertilizer to stimulate first growth. Gelambi’s dispersion study observed that pioneer species of trees were among the most frequently found in the seed traps set for bats.
But whether or not the dispersed seeds actually germinate and contribute a lot to forest regrowth remains a crucial question, and one that hasn’t been answered well by previous studies, says Karen Holl, a professor of environmental studies at the University of California, Santa Cruz. “To really have an impact, the seeds have to establish,” she says. And that seeding needs to be documented and quantified.
In her view, much more rigorous testing and evidence is needed to prove that fauna attraction methods contribute significantly to reforestation. Such experiments “would need to be [conducted] over a larger spatial scale and a longer time scale and measure recruitment. … That’s really what [researchers] need to be doing to demonstrate these [lures] work.”
There are numerous barriers that newly dispersed seeds face before a degraded area can be transformed into a new forest. Among these challenges is the competition tree seeds face from grasses and other vegetation. Seed predation by birds and other animals is also a problem. Lures might work best when used in protected areas where ecological conditions favor regrowth, Holl says, but such long-term observations have yet to be done.
Holl argues that manually seeding or directly planting larger tree species could be a “much better” lure and restoration strategy. That conclusion is based on her own long-term project that focused on planting tree nuclei (or patches) on degraded land in Costa Rica. Those tree patches have proven effective at attracting seed dispersers, particularly birds and bats, over time. The patches have other advantages: They “attract the fauna, shade out pasture grasses and overcome barriers to trees,” she notes.
Parolin says her team is currently investigating seed recruitment effectiveness in Brazil, testing essential oil lures and monitoring how well new trees grow.
Gelambi agrees that the use of scents to attract seed dispersers is a technique still in its infancy. “Additional studies are needed to evaluate how effectively this approach works across various environments and over extended periods,” she says, and work must be done to attract different species of bat. “It may take several years to validate these findings and develop strategies for real-world applications.”
She suggests that maximizing reforestation may also require a mix of techniques depending on locale and situation, including chemical or natural attractants, plus the planting of trees that attract bats, birds and other seed dispersers.
Researchers in Brazil are planning a new project this year that will deploy essential oil lures in forested and degraded areas to determine if other seed-dispersing mammals, such as marsupials, are attracted to the test sites and “hopefully increase the diversity of seed dispersal,” Parolin says.
“In the short term, our lures offer a practical application for bat researchers,” Gelambi says. “By purchasing these [synthetic] molecules, researchers can attract bats to study their communities or address other ecological questions.”
Large birds can boost forest carbon storage — if deforestation doesn’t interfere
Citations:
Parolin, L. C., Lacher, T. E., Bianconi, G. V., & Mikich, S. B. (2021). Frugivorous bats as facilitators of natural regeneration in degraded habitats: A potential global tool. Acta Oecologica, 111, 103748. doi:10.1016/j.actao.2021.103748
Schubert, S. C., Zahawi, R. A., Oviedo‐Brenes, F., Rosales, J. A., & Holl, K. D. (2024). Active restoration increases tree species richness and recruitment of large‐seeded taxa after 16–18 years. Ecological Applications, 35(1). doi:10.1002/eap.3053
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