- Researchers recorded thousands of hours of sounds in areas that had been logged, burned once and burned multiple times along the “arc of deforestation” in the Brazilian Amazon.
- In the forests with repeated fires, animal communication networks were quieter, with less diversity of sound than in logged forests or forests burned only once. This type of acoustic monitoring can be used as a cost-effective way to check the pulse of the forest.
- The authors were surprised to find that insects, not birds, were the most obvious signal of forest degradation. Additionally, they found that amount of biomass in a forest doesn’t correlate with the level of biodiversity.
- There’s a major difference in the biodiversity of a forest after one burn versus multiple burns, one author said, so protecting forests from repeated fires is still worthwhile.
The rainforest is dense with sound. Like musicians in an orchestra, each animal plays a part, occupying its own “acoustic niche” in both frequency and time. But repeated fires are silencing the symphony, according to a new study published in the Proceedings of the National Academy of Sciences.
Researchers from the University of Maryland recorded thousands of hours of sounds in the Amazon Rainforest. They looked at three types of forests: those that had been logged, burned once, and burned multiple times. All were located along the “arc of deforestation,” an area along the southeastern edge of the Brazilian Amazon where development pressures such as cattle ranching are encroaching into the last remaining vestiges of intact forest.
“Sounds are a pretty good indicator of what species are around you, especially in rainforest, where there is huge diversity,” study co-author Anshuman Swain, a University of Maryland ecologist, told Insider.
The recordings highlighted a stark difference in animal sounds between forests that had experienced multiple fires versus only one fire. In the forests with repeated fires, animal communication networks were quieter, with less diversity of sound than in logged forests or forests burned only once.
“Being in these forests that were repeatedly burned was so strikingly different … you could feel that disequilibrium … it’s just extremely eerie and haunting how these forests are becoming empty,” lead author Danielle Rappaport, chief research and innovation officer at the Amazon Investor Coalition, told Mongabay. “They’re emptying out.”
The researchers analyzed how diverse the sounds were throughout the day and how they interacted, allowing them to preserve the complexity of the soundscape without identifying individual species. Forests with repeated burning sounded homogenous, with fewer instruments in the orchestra and movements in the symphony.
This method of acoustic monitoring, Swain said, is “a low-cost indicator of how badly we have damaged the environment.”
Before heading in to record, the researchers studied the forests from above. They looked at past satellite images to determine the frequency and severity of fires and logging in past years, and used lidar, a remote-sensing technology that employs lasers, to measure how much carbon was stored in the vegetation.
Rappaport said they were surprised to find the amount of vegetation, or biomass, doesn’t correlate with the level of biodiversity. In short, more trees don’t necessarily mean a more diverse animal community.
The study does “groundbreaking work to show that the plant biomass, on its own, is not a one-to-one proxy for biodiversity change and that logged and multiply-burned forests respond differently in terms of their biodiversity loss,” Woody Turner, a program scientist at NASA’s biological diversity Earth science division, who was not involved in this research, told Mongabay.
The other big surprise was that insects, not birds, were the most obvious signal of forest degradation from the acoustic record.
“That that really speaks to the importance of the insects as the ultimate canary in the coal mine,” Rappaport said. “We know that insects are experiencing cataclysmic declines globally, and this just underscores the importance of actually listening to them.”
Typically, acoustic monitoring is used to record bird populations, especially during their peak singing hours, the dusk and dawn choruses. But the research team found that it was the periods of time least sampled by biologists, the windows in the middle of the day and in the night, that served as most important barometers of change.
The study, Turner said, demonstrates how useful acoustic remote sensing is for detecting and monitoring changes in insect diversity, “which is critical as insects are the most diverse taxa in our most biodiverse terrestrial ecosystems: moist tropical forests.”
Fires aren’t a naturally occurring phenomenon in the Amazon; they’re often set by farmers and ranchers to clear the land for agriculture. However, in recent years, deforestation and climate change have degraded and dried intact forests, and fires are escaping into standing rainforest.
Still, Rappaport said, these forests have value, and we need to move beyond the binary of thinking of forests as either intact or degraded.
“There’s a major difference in terms of the ecosystem that Amazon forest can support after one burn, versus two burns,” Rappaport said, “so protecting forests from repeated fires will have massive co-benefits, both from a carbon perspective and biodiversity perspective.”
Banner image: A blue-grey tanager (Thraupis episcopus) in Peru. Image by Rhett A. Butler/Mongabay.
Rappaport, D. I., Swain, A., Fagan, W. F., Dubayah, R., & Morton, D. C. (2022). Animal soundscapes reveal key markers of Amazon forest degradation from fire and logging. Proceedings of the National Academy of Sciences, 119(18), e2102878119. doi: 10.1073/pnas.2102878119
Liz Kimbrough is a staff writer for Mongabay. Find her on Twitter @lizkimbrough_
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