- The island of Madagascar is a hotspot for animal and plant biodiversity, but since the 1950s it has suffered high rates of deforestation.
- Once damaged, these forests are susceptible to takeover by a nonnative plant invader, the strawberry guava tree originally from Brazil.
- The guavas produce delicious fruit that the lemurs relish and whose seeds the lemurs themselves help to spread.
- Conservationists say forest restoration, critical to the survival of lemurs, needs to take into account the pernicious effects that strawberry guavas have on the ecology of forests — both those that are still intact, and those that are being restored.
Madagascar is renowned for its lemurs, which are threatened due to hunting and deforestation. Restoring native forests to ensure their survival is critical, but once damaged, forests in Madagascar are vulnerable to takeover by invasive guava trees — whose seeds the lemurs themselves are helping to spread.
When the delicious strawberry guavas (Psidium cattleyanum) are in fruit, lemurs will choose them over native fruit, says Amy Dunham, a biologist at Rice University in the U.S.
On her last visit to Ranomafana National Park, in southeastern Madagascar, Dunham, who has been doing fieldwork there for more than 30 years, filmed an endangered Milne-Edwards’ sifaka (Propithecus edwardsi), a large lemur with a dark-brown and cream-colored coat, a black hairless face, and penetrating orange eyes. The sifaka was sitting in a thick guava patch munching on one of the ruby-red fruits.
“For me, [the video] captures a big part of the picture,” Dunham says. “An endangered lemur can benefit from an invasive plant that is simultaneously undermining the long-term biodiversity and functioning of the forest.”
Dunham and colleagues carried out a study in Ranomafana in 2024 that found that where strawberry guavas, originally from Brazil, had taken hold, they created thick, impenetrable patches in areas of forest that had been disturbed as far back as the 1930s. These thickets, which Dunham refers to as “monocultures,” drain key nutrients from the soil, suppress the growth of native plants, and strip away the diversity of insects and other invertebrates.
The loss of insect diversity means native animals are robbed of an essential source of protein. Not just lemurs, but also birds and tenrecs, a group of mammals, some of them resembling hedgehogs, that evolved in Madagascar and depend on insects for a large portion of their diet.
Outcompeting native trees
Although it’s still unclear whether guavas pose as big a threat to parts of the forest that are still intact, if a tree does happen to fall — say, during a cyclone — guava seeds deposited in that part of the forest via lemur dung could germinate and quickly fill the gap by outcompeting native plants in the new clearing.
“We often think about the lemurs, but not all the rest of the biodiversity in those forests,” Dunham says. Madagascar is “one of the hottest hotspots for plant diversity,” she adds, and that diversity is as important to protect and preserve as the lemurs, whose own survival depends upon it.
Take mistletoes. At least 16 different species of these epiphytic plants grow high up in the forest canopy in undisturbed parts of Ranomafana, clinging to the branches of native trees. The mistletoes, known in Malagasy as tongoalahy, in turn provide leaves, fruit and flowers that lemurs and a host of other animals feed on.
In a separate study led by Malagasy ecologist Zo Fenosoa, and co-authored by Dunham, the team staked out sites in Ranomafana where three different species of mistletoes grow, and watched as 30 different species of birds, and seven different species of lemurs visited them. Some ate the fruits, others the nectar or the leaves; others foraged on the insects attracted to the plants.
Among those that ate the fruit were nocturnal brown mouse lemurs (Microcebus rufus) and Crossley’s dwarf lemurs (Cheirogaleus crossleyi); and by day, lesser vasa parrots (Coracopsis nigra), Madagascar blue-pigeons (Alectroenas madagascariensis) and Malagasy bulbuls (Hypsipetes madagascariensis).
Mistletoes are “keystone resources,” the study found, sustaining all of these species while also providing a staple food source for larger sifaka lemurs in times of food scarcity.
In guava-invaded patches, however, there are no mistletoes. Guava stems and branches shed their bark, depriving the sticky mistletoe seeds of a secure place to latch onto and grow.
Since the 1950s, large areas of Madagascar’s native forests have been lost to or degraded by agriculture and timber extraction. The island still loses an estimated 200,000 hectares (nearly 500,000 acres) annually. This leaves the way open for the spread of strawberry guavas.
Even if guava roots are successfully removed from forest restoration sites, their fallen leaves and fruit leave behind allelochemicals in the soil that are toxic to other plants.
“If guava dominates [forest] regeneration,” Dunham says, “we risk rebuilding forests that are structurally and ecologically simplified, with fewer resources for native species.”
Biochar a potential solution
There could be a solution. On the Indian Ocean island of Mauritius, more than 1,000 kilometers (600 miles) east of Madagascar, strawberry guavas are also threatening remnant native forest patches. But in 2017, at sites in Black River Gorges National Park, a team led by Mauritian ecologist Lutchmee Sujeeun found that spreading biochar, a soil-boosting charcoal made from plant waste, in areas where guava trees had been removed reduced the effects of the guava allelochemicals and promoted the growth of native plants.
The biochar Sujeeun used was made from coconut husks; if it were ever to be scaled up, an obvious source would be the cut stems of the guava trees themselves.
However, she cautions that the dosages of biochar needed, and the effects it has on native plants and animals, as well as on different soil types, still need to be thoroughly assessed. Biochar’s application at scale, whether in Madagascar or Mauritius, would prove costly and labor-intensive, combined as it would be with the physical removal of the guava trees.
“The best option is to identify areas and species that are most likely to show large positive responses to biochar applications,” Sujeeun says.
Anthropologist Cortni Borgerson, an associate professor at Montclair State University in the U.S., who wasn’t part of Dunham’s guava study in Ranomafana, says vulnerable brown lemurs (Eulemur fulvus) love strawberry guavas so much that hunters even use the fruit to bait traps set for them along a central part of the island’s eastern coastal region.
“Like the bait in a trap, the guava lures Madagascar’s remaining frugivores to endanger the very forests on which they depend,” Borgerson tells Mongabay in an email from Masoala National Park, in the northeast of the island.
“The key to long-term resilience [of Madagascar’s native ecosystems] lies in restoring that extraordinary biodiversity, starting with native plants,” she adds. “It will take a massive effort to remove this invasive species, but dedicated, passionate people like the authors of [the guava] study are producing the exact science we need to make a difference.”
Banner image: A lemur eating a strawberry guava. Image courtesy of Natalee Phelps.
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Citations:
McCary, M. A., Fenosoa, Z. S., Montaquila, J., Wuesthoff, E. F., Rajeriarison, E., Matsuda, E., & Dunham, A. E. (2026). Invasive strawberry guava (Psidium cattleyanum) disrupts forest recovery and invertebrate biodiversity in Madagascar’s threatened rainforest ecosystem. Biological Conservation, 315, 111703. doi:10.1016/j.biocon.2026.111703
Fenosoa, Z. S. E., Razafindratsima, O., Rakotomanana, H., Razafindraibe, H., Rasamisoa, D., & Dunham, A. (2020). Birds and lemurs as potential seed dispersers of mistletoe in Madagascar’s rain forests. Recherches Pour le Development, 28, 49-63. Retrieved from http://cidst.recherches.gov.mg/IMG/doc/SB_28_TI.pdf#page=49
Sujeeun, L., & Thomas, S. C. (2022). Biochar rescues native trees in the biodiversity hotspot of Mauritius. Forests, 13(2), 277. doi:10.3390/f13020277
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