Temporal Soundscape Patterns in a Panamanian Tree Diversity Experiment: Polycultures Show an Increase in High Frequency Cover

Abstract

In this ecoacoustic study we used the setting of a tropical tree diversity planted forest to analyze temporal patterns in the composition of soundscapes and to test the effects of tree species richness on associated biodiversity measured as acoustic diversity. The analysis of soundscapes offers easy, rapid and sustainable methods when assessing biodiversity. During the last years the quantification of regional or global acoustic variability in sounds and the analysis of different soundscapes has been evolving into an important tool for biodiversity conservation, especially since case studies confirmed a relationship between land-use management, forest structure and acoustic diversity. Here we analyzed soundscapes from two seasons (dry and rainy season) and aurally inspected a subset of audio recordings to describe temporal patterns in soundscape composition. Several acoustic indices were calculated and we performed a correlation analysis and a non-metric multidimensional scaling analysis to identify acoustic indices that: (i) were complementary to each other and such represented different aspects of the local soundscapes and (ii) related most strongly to differences in acoustic composition among tree species richness, season and day phase. Thus, we chose “High Frequency Cover,” “Bioacoustic Index,” and “Events Per Second” to test the hypothesis that acoustic diversity increases with increasing tree species richness. Monocultures differed significantly from polycultures during night recordings, with respect to High Frequency Cover. This index covers sounds above 8 kHz and thus represents part of the orthopteran community. We conclude that increasing tree species richness in a young tropical forest plantation had positive effects on the vocalizing communities. The strongest effects were found for acoustic activity of the orthopteran community. In contrast to birds, orthopterans have smaller home ranges, and are therefore important indicator species for small scale environmental conditions.

Using acoustic indices in ecology: Guidance on study design, analyses and interpretation

“…This has also been termed the 'objective soundscape' and is the focus of the current paper. This contrasts with the 'subjective soundscape', which refers to the acoustic environment as perceived by individual organisms within it, see Farina et al (2021) and Grinfeder et al (2022) Spectrogram A visual representation of the matrix derived by converting a raw audio recording using a Fast Fourier Transform, with time on the x-axis, frequency on the y-axis and amplitude values in each cell reflected with a colour or intensity gradient (Sueur, 2018) Sousa -Lima, et al, 2021;Gasc et al, 2018;Gottesman et al, 2021;Rappaport et al, 2022), track habitat recovery following restoration (Borker et al, 2020;Lamont et al, 2022;Müller et al, 2022) and assess the suitability of that habitat for particular species in the future (Znidersic & Watson, 2022).…”

“…Acoustic indices characterise the soundscape or facets of the acoustic community and have successfully provided ecological insights without requiring species‐specific identifications. For example, using acoustic indices it is possible to discriminate among habitat types (Bradfer‐Lawrence et al, 2019; Do Nascimento et al, 2020; Eldridge et al, 2018; Metcalf et al, 2021), monitor the impacts of habitat disturbance (Burivalova et al, 2021, 2022; Duarte, Sousa‐Lima, et al, 2021; Gasc et al, 2018; Gottesman et al, 2021; Rappaport et al, 2022), track habitat recovery following restoration (Borker et al, 2020; Lamont et al, 2022; Müller et al, 2022) and assess the suitability of that habitat for particular species in the future (Znidersic & Watson, 2022).…”

Enhancing the structural diversity between forest patches—A concept and real‐world experiment to study biodiversity, multifunctionality and forest resilience across spatial scales

“…the future (Messier et al, 2022). Moreover, variation in light and deadwood affects assembly processes (Bässler et al, 2016;Müller et al, 2022). Keeton (2006) However, evidence for a causal chain from natural disturbances to BEF across scales is still limited, mainly because studies on natural disturbances often lack a properly replicated design, and simply do not often combine changes in β-diversity with variation in ecosystem functioning.…”

“…A number of these tree species are those expected to be suitable under warmer conditions in the future (Messier et al, 2022). Moreover, variation in light and deadwood affects assembly processes (Bässler et al, 2016; Müller et al, 2022).…”