From space, parts of the Amazon rainforest that have previously been logged or burned may look fully recovered with a healthy, lush, and green canopy. They may seem to be places buzzing with activity and full of sounds. But inside the rainforest the animal life may tell a different story of damage to their environment through a quieter soundscape.
Scientists from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the
University of Maryland, College Park, investigated how the acoustics of a
forest can be a cost-effective indicator of its health.
From space, parts of the Amazon rainforest that have previously been logged or burned may look lush and green, like a place buzzing with activity and full of sounds. But inside the rainforest, the animal life may tell a different story, of a harsh environment and a quieter soundscape. Credits: NASA's Goddard Space Flight Center Download this video in HD formats from NASA Goddard's Scientific Visualization Studio
Danielle Rappaport, then a doctoral student at the University of Maryland and now co-founder of the Amazon Investor Coalition, led this research beginning in 2016. She and her team combined acoustic data collected under the forest canopy with tree height measurements from aircraft flights and space-based observations of logging or fires from Landsat satellites. Landsat is a long-running partnership between NASA and the U.S. Geological Survey.
In forests that were burned multiple
times, recordings of animal noises were quieter than in intact forest
locations, leaving gaps in the soundscape and indicating that species that
had been present before were now gone. As Rappaport ventured into these
previously burned parts of the rainforest to place the recorders for the
scientific measurements, she said she could feel the differences.
“I've been working with tropical forests
all my professional life,” Rappaport said. “I've never quite been to a forest
that was this devastated. It’s something that you can smell, you can hear, it's
everywhere.”
Scientist Danielle Rappaport is using a combination of satellite data and
acoustic recordings to study the health of the Amazon. Credits: Courtesy
of Danielle Rappaport
On the first day of trekking through a forest that had been burned five
times throughout the study period, Rappaport’s field assistant temporarily quit
due to the oppressive nature of the environment. The environment was harsher in
forests that had been burned several times, Rappaport said. The forest
undergrowth was thick and difficult to navigate, and insects such as sweat bees
surrounded her. However, these on-the-ground differences in the animal
environment aren’t observable when forests are measured from space, where the
regrown canopy appears almost as green and complete as before the fires.
Instead of choosing specific times of day to target acoustic signatures of
well-known species, Rappaport and her team chose to place and leave recorders
in degraded forests for extended periods to gather a fuller, species-inclusive
repertoire of sound. When analyzed together, these recordings revealed unique
ecological fingerprints, or soundscapes. Species of frogs, insects, birds, and
primates each occupy sound space in different ways – ways that enable
biodiversity and ecological systems to be analyzed without scientists being
physically present.
“You can think of the animal soundscape as an orchestra,” Rappaport said.
“The flutes occupy a different time of day and a different frequency band than
the oboes.”
Her team developed a new way to quantify forest health by analyzing
soundscapes with a network theory approach. This means that by using
the digital soundscape as a whole – the orchestral music –
Rappaport’s team could understand the relationship between the level of impacts
and the community of species – the character and quality of the instruments
playing – without requiring all the species to be identified.
“It’s one more step towards understanding the sound community without
needing to know which individual species are there because we’re starting to
listen for them in ways that help us connect the coordinated production of
sound, even if we don’t know who’s making the noise,” said Doug Morton, an
Earth scientist at NASA Goddard and Rappaport’s PhD advisor.
Knowing where to place the recorders, and how to interpret the diversity of
soundscapes, required additional data from lidar measurements taken between
2013 and 2016 and the past 33 years of Landsat satellite records.
“Our ability to analyze decades of history through the Landsat data record
provided a strong backbone to this work,” Rappaport said.
The Landsat program, which marked its 50th anniversary in
space this July, allowed the scientists to see back in
time. The scientists created a timeline of Amazon forest cover for the past
three decades, and used the history of forest degradation to determine where to
place the recorders. With these data, the team sampled sounds from locations
with varying levels of fire and logging activity.
Lidar measurements explain the diversity of soundscapes by providing a
three-dimensional representation of the forest’s canopy. Airplanes flew over
the forested areas, collecting tree height data that helped determine the
layers of the forest between the canopy and the ground.
“That three-dimensional picture still carries a memory of some of those
historic disturbances,” Morton said.
These three quantitative datasets layered together helped Rappaport and her
team better understand the ecosystem structure of Amazon forests impacted by
human activity.
They found that repeatedly burned forests had less biodiversity than
forests that were logged once. For example, with each additional forest fire,
the soundscape becomes quieter. After logging, the forest soundscape suggested
a capacity to recover animal diversity.
Rappaport and her team hope this new technique will open up a new
understanding of forest biodiversity that is threatened by fires and logging,
and about the relationship between biodiversity and carbon stored in Amazon
forests over time. Soundscapes provide a relatively cost-efficient and rapid
means of estimating levels of biodiversity in complex and generally
species-rich tropical environments.
“Sound data add a new dimension to our understanding of the Amazon,” Morton
said. “I’m fascinated by what we still have to learn.”
By Erica McNamee NASA's Goddard Space Flight Center, Greenbelt, Md.
Source: NASA
Data, Acoustic Soundscapes Assess Health of Amazon Rainforest | NASA
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