Tuesday, July 18, 2023

Animal Soundscapes: Monitoring Amazon Forests After Fire and Logging

Environmental & Science Education, STEM, Biodiversity, Nature, Wildlife, Nature of Science, History of Science

Ed Hessler

From space, previously logged and/or burned sections of the Amazon rainforest look as lush and as green as the rest of the forest., i.e., normal, booming and buzzing with activity. However, on the ground, inside, animal life reveals a different story: the soundscape is quieter than its surrounding untouched rainforest.

Research reported by D. I. Rappoport and others in the Proceedings of the National  Academy of Sciences (PNAS 119:18, 2022) demonstrates the importance of biomonitoring, i.e., collecting data over time as well as collecting data over 24h periods. 
The focus of the research is on the bioacoustic environment following such interventions as logging and fire. "The emergent 24-h patterns of acoustic activity differed between logged and burned forests, and we observed large and sustained shifts in acoustic community assembly after multiple fires. Soundscape differences among degraded forests were clearest during insect-dominated hours rarely sampled in field studies of biodiversity."

Rappaport and her team made "multiday acoustic recordings (214 24-h surveys) during September and October 2016 in 39 forests with different times since logging (4 to 23 y) and histories of fire activity (1 to 5 fires) entered once to place and leave sound collecting recorders in degraded forests for extended periods of time."  The result was data rich: a "data record of 30,816 1-min recordings" was made. This was combined with previously existing airborne lidar data.

"The authors report that their findings demonstrate that soundscapes encode digital markers of the history of degradation from human activity, revealing distinct patterns of community change following logging and fire. This study paves the way for more widespread use of ecoacoustics to benchmark and monitor changes in acoustic community composition in human-altered tropical forest landscapes, especially in remote regions with many unknown species."

One finding by the team of the difference between logging and burned forests was that "overall, fire resulted in more empty acoustic niches across the 24-h soundscape than logging, and recurrent burns led to a major restructuring of the acoustic community."  

In the introduction to the research report, the authors note that "addressing the tropical biodiversity extinction crisis...requires an efficient, distributed, long-term monitoring system to assess ecosystem structure. Traditional, ground-based biodiversity inventories are logistically prohibitive to conduct at scale, and limited taxonomic expertise perpetuates large data discrepancies for lesser known taxa (see text below for use of term pseudotaxa which means not known), such as insects, which constitute the bulk of tropical biodiversity. Advances in the emerging discipline of acoustic remote sensing, or ecoacoustics, may permit large-scale biodiversity monitoring for multiple taxa, including unidentifiable  species, based on the aggregate sound signature of the animal community, or soundscape (see below for use of term pseudotaxa for them, i.e., not known)

In a report on the research in The Earth Observer (September - October 2022, 34(5), pp 38 and 39), Rappoport called attention to one of the difficulties of on the ground biomonitoring: "the forest undergrowth was thick and difficult to navigate and she was "surrounded by insects." There is a photo of her face and head covered by sweat bees. In this kind of research the recording equipment can be placed, left and then collected later for analysis in the laboratory. This reduces the period of discomfort considerably although probably not enough for many of us.

This media report from the University of Maryland's College of Computer, Mathematical and Natural Sciences includes photographs taken in the field of Dr. Rappaport and of the sensors used which show the difficult walking conditions. In addition there is a short movie on listening to what Dr. Rappaport calls a "sound orchestra".  
About such orchestras she said in The Earth Observer article linked above she said  “You can think of the animal soundscape as an orchestra. The flutes occupy a different time of day and a different frequency band than the oboes.”  The report notes that she and "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—i.e., hearing the music from the whole orchestra—Rappaport’s team could understand the relationship between the level of impacts and the community of species—i.e., the character and quality of the individual instruments playing—without requiring all the species to be identified."

And here is information about Dr. Danielle Rappoport.

If you would like to know more about soundscape ecology an article in the journal Bioscience (2011) about the then emerging discipline provides an introduction.

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