What is soundscape ecology? An introduction and overview of an emerging new science

We summarize the foundational elements of a new area of research we call soundscape ecology. The study of sound in landscapes is based on an understanding of how sound, from various sources—biological, geophysical and anthropogenic—can be used to understand coupled natural-human dynamics across different spatial and temporal scales. Useful terms, such as soundscapes, biophony, geophony and anthrophony, are introduced and defined. The intellectual foundations of soundscape ecology are described—those of spatial ecology, bioacoustics, urban environmental acoustics and acoustic ecology. We argue that soundscape ecology differs from the humanities driven focus of acoustic ecology although soundscape ecology will likely need its rich vocabulary and conservation ethic. An integrative framework is presented that describes how climate, land transformations, biodiversity patterns, timing of life history events and human activities create the dynamic soundscape. We also summarize what is currently known about factors that control temporal soundscape dynamics and variability across spatial gradients. Several different phonic interactions (e.g., how anthrophony affects biophony) are also described. Soundscape ecology tools that will be needed are also discussed along with the several ways in which soundscapes need to be managed. This summary article helps frame the other more application-oriented papers that appear in this special issue.     

Soundscapes of urban parks: An innovative approach for ecosystem monitoring and adaptive management

Urban foresters are addressing the challenge of urban biodiversity loss through management plans in the context of rapid urbanization. Protecting the integrity of the urban ecosystem requires long-term monitoring and planning for resilience as well as effective management. The soundscape assessment has attracted attention in this field, but applying the soundscape assessment in urban ecological monitoring requires a protocol that links soundscapes to the impact of resource management on biodiversity over time. The effective processing and visualization of large-scale data also remains an important challenge. The aim of this study was to better understand the relationship between soundscape and physical environment, and examine the feasibility of this innovative soundscape approach in highly urbanized areas. Soundscape recordings were collected for 20 urban parks twice on 4 consecutive days in Spring. A total of 691,200 min of sound material were automatically obtained. In order to track the spatio-temporal patterns of a soundscape and determine its potential suitability for ecosystem monitoring, our study characterized soundscape information by adopting 4 widely used acoustic indices: acoustic diversity index (ADI), bioacoustic index (BIO), normalized difference vegetation index (NDSI), and power spectral density (PSD). Daily patterns of PSD have provided a potential connection between soundscapes and bird songs, and 1–2 kHz presented a similar pattern that was linked to human activity. Through further modeling, we tested the relationship of soundscapes to physical environment characteristics. The results showed the importance of habitat vegetation structure for acoustic diversity. More vertical heterogeneity, with an uneven canopy height or multilayered vegetation, was associated with more acoustic diversity. This suggests that clearing ground cover may have a significant negative impact on wildlife. Our results suggest that soundscape approaches provide a way to quickly synthesize large-scale recording data into meaningful patterns that can track changes in bird songs and ecosystem conditions. The proposed approach would enable regular assessment of urban parks and forests to inform adaptive planning and management strategies that can maintain or enhance biodiversity.     

Research on spatiotemporal variation characteristics of soundscapes in a newly established suburban forest park

Passive acoustic monitoring has developed rapidly as a tool for ecological assessments, and the use of acoustic indices to assess biodiversity in urban forests promises to be a low-cost and efficient analytical approach. However, the accuracy of using acoustic indices to characterize biodiversity may be compromised by excessive human interference. The acoustic complexity index (ACI) and normalized difference soundscape index (NDSI) were chosen to determine their application value, and explore the spatiotemporal patterns of change in the soundscape of a newly established suburban forest park in China. To understand the influence of drivers such as different sound source types, road distance, and vegetation structure on the soundscape, the Eastern Suburb Forest Park was selected as the study area, and 55 recording points (200 m intervals, 5 × 11 grids) were set up using a systematic grid. Passive acoustic monitoring was performed for four consecutive days in each season, and the spatiotemporal variation of the soundscape was visualized based on indices interpolation. The results showed that when using ACI and NDSI to rapidly assess biodiversity in urban forest environments, attention needs to be paid to the implications of seasonal fluctuations on indices. The temporal variation of the soundscape was closely related to the natural rhythms and vocal activity intensity of organisms. Distance to a nearby main road, distance to water, and structural complexity of vegetation were key factors influencing spatial variation. The findings support the use of acoustic methods to assess the characteristics of soundscapes in human-built urban forests. Soundscape mapping visualizes hotspots and moments of ecoacoustic activity, and has great potential for development in the conservation and management of suburban forest soundscapes.     

Linking ecological condition and the soundscape in fragmented Australian forests

Natural landscapes are increasingly subjected to anthropogenic pressure and fragmentation resulting in reduced ecological condition. In this study we examined the relationship between ecological condition and the soundscape in fragmented forest remnants of south-east Queensland, Australia. The region is noted for its high biodiversity value and increased pressure associated with habitat fragmentation and urbanisation. Ten sites defined by a distinct open eucalypt forest community dominated by spotted gum (Corymbia citriodora ssp. variegata) were stratified based on patch size and patch connectivity. Each site underwent a series of detailed vegetation condition and landscape assessments, together with bird surveys and acoustic analysis using relative soundscape power. Univariate and multivariate analyses indicated that the measurement of relative soundscape power reflects ecological condition and bird species richness, and is dependent on the extent of landscape fragmentation. We conclude that acoustic monitoring technologies provide a cost effective tool for measuring ecological condition, especially in conjunction with established field observations and recordings.     

Spatial heterogeneity of ambient sound at the habitat type level: ecological implications and applications

While spatial heterogeneity is one the most studied ecological concepts, few or no studies have dealt with the subject of ambient sound heterogeneity from an ecological perspective. Similarly to ambient light conditions, which have been shown to play a significant role in ecological speciation, we investigated the existence of ambient sound heterogeneity and its possible relation to habitat structure and specifically to habitat types (as syntaxonomically defined ecological units). Considering that the structure and composition of animal communities are habitat type specific and that acoustic signals produced by animals may be shaped by the habitat’s vegetation structure, natural soundscapes are likely to be habitat specific. We recorded ambient sound in four forest and two grassland habitat types in Northern Greece. Using digital signal techniques and machine learning algorithms (self organizing maps, random forests), we concluded that ambient sound is not only spatially heterogeneous, but is also directly related to habitat type structure, pointing towards the existence of habitat type specific acoustic signatures. We provide evidence of the importance of soundscape heterogeneity and ambient sound signatures and a possible solution to the social cues versus vegetation characteristics debate in habitat selection theory.     

Soundscape in a context of acoustic and landscape ecology

Soundscape ecology is being proposed as a new synthesis that leverages two important fields of study: landscape ecology and acoustic ecology. These fields have had a rich history. Running “in parallel” for over three decades now, soundscape ecology has the potential to unite these two (among other) fields in ways that provide new perspectives on the acoustics of landscapes. Each of us was involved in the “birth” of these two fields. We each reflect here on the rich history of landscape ecology and acoustic ecology and provide some thoughts on the future of soundscape ecology as a new perspective.     

Spatial-temporal change analysis of plant soundscapes and their design methods

The aim of the study was to describe the soundscape elements, spatial-temporal changes and preferences in plant soundscape using quantitative measures, in order to recommend soundscape design methods. Both acoustic measurements and subjective evaluations of the soundscapes were conducted at various locations in Jinan Forest Park using 14 groups of plant spaces within the park. Our analysis investigated soundscape elements categorized as nature sounds, human activity sounds, and mechanical sounds. The soundscapes varied with time of day and season and were influenced by the surrounding environment and human behavior. Soundscape element preferences were correlated with a visitor’s age and visitation frequency, with nature sounds receiving the highest preference scores. Closed nature spaces had lower sound levels and received the highest preference by visitors. The results were further analyzed according to five soundscape methods to improve visitor experience: sound-masking, sound-borrowing, sound-reinforcement, sound-contrasting, and sound-expectation, that are also consistent with Chinese classical garden design.     

Beyond noise mitigation: managing soundscapes as common-pool resources

The extent of noise and its impacts continues to grow globally indicating a different approach from regulating individual noise sources is needed. We pose the argument that soundscapes, or the acoustic environment, should be managed as a common-pool resource (CPR). Using CPR theory, we argue that soundscapes possess key features of CPRs: (1) multiple soundscape users, (2) difficulty of exclusion, and (3) subtractability and degradation. Using Ostrom’s Social-Ecological Systems (SES) framework, we describe the main elements of soundscapes to consider for their sustainable management. In order to assess noise issues and challenges in managing national park soundscapes, we conducted interviews with U.S. National Park Service managers at parks identified as having air tour overflight impacts. While most managers indicated that aircraft overflights posed the most serious impacts to park resources and visitor experiences, the park units also experienced several other types of noise impacts including traffic on park roads, park maintenance operations, and different types of motorized recreational vehicles. Addressing single sources of noise is necessary, as is the case with air tour overflights, but we argue that a more comprehensive approach is needed to protect park soundscapes. From this study several SES framework variables emerged that need to be addressed for sustainable management, such as the lack of clear soundscape boundaries, availability of acoustic monitoring and data, and the number and types of soundscape users. Based on CPR theory and using the SES framework, the challenges and a potential new approach for sustainable management are discussed.     

Temporal and spatial variation of a winter soundscape in south-central Alaska

Context

Winter soundscapes are likely different from soundscapes in other seasons considering wildlife vocalizations (biophony) decrease, wind events (geophony) increase, and winter vehicle noise (technophony) occurs. The temporal variation and spatial relationships of soundscape components to the landscape in winter have not been quantified and described until now.

Objectives

Our objectives were to determine the temporal and spatial variation and acoustic–environmental relationships of a winter soundscape in south-central Alaska.

Methods

We recorded ambient sounds at 62 locations throughout Kenai National Wildlife Refuge (December 2011–April 2012). We calculated the normalized power spectral density in 59,597 recordings and used machine learning to determine acoustic–environmental relationships and produce spatial models of soundscape components.

Results

Geophony was the most prevalent component (84 %) followed by technophony (15 %), and biophony (1 %). Geophony occurred primarily at night, varied little by month, and was strongly associated with lakes. Technophony and biophony had similar temporal variation, peaking in April. Technophony occurred closer to urban areas and at locations with high snowmobile activity. Biophony occurred closer to rivers and was inversely related to snowmobile activity. Over 75 % of sample sites had >1 recordings of airplane or snowmobile noise, mainly in remote areas.

Conclusions

The soundscape displayed distinct patterns across 24-h and monthly timeframes. These patterns were strongly associated with land cover variables which demonstrate discrete acoustic–environmental relationships exhibiting distinct spatial patterns in the landscape. Despite the predominance of geophony, the presence of technophony in this winter soundscape may have significant negative effects to wildlife and wilderness quality.

     

Spatio-temporal variability in human and natural sounds in a rural landscape

The study of landscape structure and functions, including the underlying ecological and anthropogenic processes has traditionally relied on visual aspects without considering information of non-visionary cues, e.g. auditory. In this work we applied a complementary approach for the study of landscapes using qualitative information for the sonic environment. In particular we studied the qualitative linkages between landscape structure and functions and daily sound patterns. The main objectives were the investigation of the spatial and temporal variability in sound perception, and the identification of the dominant sound categories (anthropogenic, biological, geophysical originated sounds) in relation to landscape characteristics. Our results showed significant spatio-temporal variability in the intensity of different sound categories, which reflects distinct soundscape patterns. Temporal sound variability reflected the daily cycle of anthropogenic activities and biological processes, whereas the spatial sound viability was mainly shaped by landscape attributes. The combination of the visual landscape information and its emergent acoustic profile enhances our perception and understanding of nature and this integrated approach may have many practical applications in landscape management, monitoring and planning.     

Measuring and interpreting the temporal variability in the soundscape at four places in Sequoia National Park

The soundscape was recorded in four selected places in Sequoia National Park CA, to quantify and assess the diurnal and seasonal character of the park’s soundscape. The recording sites were selected to represent a combination of elevation and vegetation diversity. Hour-long sound recordings were made by four individuals at each place during fall, spring, summer and winter at dawn, midday, dusk, and midnight with identical recording instrumentation. The recordings of the soundscape were made in an old growth forest (Crescent Meadow), in a foothill oak savanna (Sycamore Spring), in an upland savanna chaparral (Shepherd Saddle) and in a foothill riparian location adjacent to the Kiawah River (Buckeye Flat). Sound recordings were analyzed using a normalized Power Spectral Density (PSD) algorithm and partitioned into 1 kHz intervals based on 12 subsamples from each of the 64 h-long sound recordings. Biological signals (biophony) were based on the highest PSD value within the range of 2–8 kHz. A multilevel analysis (MLA) was used to examine temporal patterns of biophony at four locations in Sequoia National Park. Unsupervised Landsat Thematic Mapper Satellite Imagery identified 25 vegetation regimes in Sequoia National Park. Satellite signatures of the habitat where recordings were made were extracted from the imagery to scale to the region.     

A primer of acoustic analysis for landscape ecologists

In this paper we present an introduction to the physical characteristics of sound, basic recording principles as well as several ways to analyze digital sound files using spectrogram analysis. This paper is designed to be a “primer” which we hope will encourage landscape ecologists to study soundscapes. This primer uses data from a long-term study that are analyzed using common software tools. The paper presents these analyses as exercises. Spectrogram analyses are presented here introducing indices familiar to ecologists (e.g., Shannon’s diversity, evenness, dominance) and GIS experts (patch analysis). A supplemental online tutorial provides detailed instructions with step by step directions for these exercises. We discuss specific terms when working with digital sound analysis, comment on the state of the art in acoustic analysis and present recommendations for future research.     

Soundscape conservation

We argue that soundscapes possess both ecological and social value and that they should be considered natural resources worthy of management and conservation. In this paper we bring together diverse bodies of literature that identify the human and ecological benefits provided by soundscapes. Sense of place, cultural significance, interactions with landscape perceptions, and wildlife wellbeing are a few of the values ascribed to soundscapes. The values and benefits of soundscapes are motivation to advance soundscape conservation and management. Given that soundscape conservation is new, we present a summary of conservation principles that need to be considered in soundscape conservation planning. These include the need to set goals, identify targets, assess condition, identify and manage threats, and conduct monitoring of the soundscape. We also argue that soundscape conservation needs to consider the soundscape within the larger mosaic of the landscape that is occupied by humans—a perspective provided by landscape ecology. We describe several different kinds of soundscapes that need to be conserved, such as natural quiet, sensitive, threatened, and unique soundscapes, and the ways that conservation planning can protect these for the future.     

Audio-visual interaction and visitor characteristics affect perceived soundscape restorativeness: Case study in five parks in China

The capacity of urban parks to contribute to soundscape restorativeness, understood here as contributions to people’s recovery from attentional fatigue and reflection on life issues, is receiving increased interest in research and policy. However, scientific understanding of the influential mechanism of perceived soundscape restorativeness is still not clear. This paper aims to explore the effects of audio-visual interaction on perceived soundscape restorativeness (PSR) of urban parks, considering visitors of different social and demographic characteristics. The research design comprises a survey of 419 visitors to five urban parks in Fuzhou, China, general structure equation modeling, and multi-group model analysis. The results show a substantial dependence of visitors’ PSR values on respective perceptions of soundscape pleasantness and eventfulness, especially soundscape pleasantness. Visual landscape characteristics showed mediating effects on the influence of soundscape pleasantness and eventfulness on the perceived soundscape restorativeness (19.3 % and 28.3 % of the total effect, respectively). Age was the most influential social and demographic characteristic affecting the PSR, followed by gender, while occupation and educational background showed only limited effects. Future development of urban parks should strongly integrate soundscape design considerations to enhance positive PSR effects for visitors.     

Soundscape effects on visiting experience in city park: A case study in Fuzhou,China

The main objective of this study was to reveal the relationships between sound/soundscape perception and public visiting experience in city parks, based on a questionnaire survey of 146 park users in West Lake park in Fuzhou, China. The results indicated that, the three visiting experience indicators, i.e., soundscape tranquil degree (STD), landscape aesthetic degree (LAD) and visiting satisfaction degree (VSD) were positively related with each other, and LAD (correlation coefficients = 0.728, p < 0.01) was more associated with VSD than STD (correlation coefficients = 0.565, p < 0.01). Perception of certain individual sounds was found in close relationships with the three indicators. Specifically, STD showed the most significant relationships with harmonious degree of individual sounds, where perception of traffic sounds showed the most negative effects, while perception of music related sounds and water sound showed positive effects. LAD was more associated with perceived occurrences of individual sounds, where traffic sounds and music related sounds showed the most significant effects again. Both perceived occurrences and dominant degree of individual sounds showed the most and equal relationships with VSD. Specifically, mechanical sounds showed the most negative effects, and dog barking showed significant negative effects too, while music related sounds could be the only kind of sound positively contributed to VSD. Social/demographical/behavioral factors and visit motivations all showed significant relationships with individual sound perception and visiting experience. Considering the effects of all associated factors, key factors were detected for each of the visiting experience indicators. All the three visiting experience indicators showed negative relationships with certain traffic sounds, while tree rustling sound was the only sound showing positive relationship with STD. Age was the most important social/demographical/behavioral factor showing positive relationships with LAD and VSD. The research results provided theoretical references for management and design of soundscapes to contribute to more satisfied experiences in city parks.     

浅析园林声景美的创造

园林是一门综合性艺术,园林美的鉴赏活动中对听觉方面的审美要求同样不能被忽视。文章在对声景美的内涵、特征和意义进行理解和分析的基础上,讨论了各种不同类型声景美的创造途径及声景意境的营造手法。     

Comparison of avian diversity between urban parks adjacent to mountain and river in the largest megacity Guangzhou,South China

Urban parks can provide a resource for maintaining and increasing bird biodiversity. However, little research has been conducted to show the differences in bird community diversity between parks adjacent to mountains and rivers in the city center of highly urbanized areas. This study analysed whether the bird composition and species diversity differed between parks adjacent to Baiyun Mountain (hillside parks) and Pearl River (riverside parks) in Guangzhou, South China. From January 2018 to December 2020, 137927 birds representing 206 species were recorded. The results indicated that the number of species and individuals of birds were higher in hillside parks than in riverside parks in each season. The number of species and individuals was also higher in hillside parks than in riverside parks in different functional groups according to bird food type, residential type, and ecological type. The number of species shared by the two types of parks was 120. The unique birds' species number in hillside and riverside parks were 67 and 19, respectively. Bird diversity in terms of richness and Shannon index was higher significantly in hillside parks than in riverside parks in summer. Principal component analysis of environmental traits of 18 parks showed that plant traits in parks have relatively high and positive contribution. Correlation analysis indicated that bird diversity was positively affected by water area, the highest altitude, habitats diversity and tree evenness in park, while negatively regulated by building coverage around each park. The top 20 most abundant bird species accounted for 87.5% of the total birds in the study period. Nycticorax nycticorax, Urocissa erythroryncha and Podiceps ruficollis were observed more frequently in hillside parks, while Pycnonotus aurigaster, Passer montanus, Acridotheres cristatellus were observed more frequently in riverside parks. Principal coordinates analysis also indicated that bird communities significantly differed between hillside parks and riverside parks. In conclusion, our findings highlight the importance of conserving mountains and rivers as buffer zones for serious anthropogenic disturbance in the city center. We propose that the conservation of hillside parks is a priority strategy for enhancing urban birds biodiversity.     

Population dynamics under increasing environmental variability: implications of climate change for ecological network design criteria

There is growing evidence that climate change causes an increase in variation in conditions for plant and animal populations. This increase in variation, e.g. amplified inter-annual variability in temperature and rainfall has population dynamical consequences because it raises the variation in vital demographic rates (survival, reproduction) in these populations. In turn, this amplified environmental variability enlarges population extinction risk. This paper demonstrates that currently used nature conservation policies, principles, and generic and specific design criteria have to be adapted to these new insights. A simulation shows that an increase in variation in vital demographic rates can be compensated for by increasing patch size. A small, short-lived bird species like a warbler that is highly sensitive to environmental fluctuations needs more area for compensation than a large, long-lived bird species like a Bittern. We explore the conservation problems that would arise if patches or reserve sizes would need to be increased, e.g. doubled, in order to compensate for increase in environmental variability. This issue has serious consequences for nature policy when targets are not met, and asks for new design criteria.     

Interrelationship of birds and habitat features in urban greenspaces in Delhi, India

Biodiversity conservation in urban areas has become significant not only because of increasing human population in urban centers but also because it is one of the innovative ways to conserve biodiversity as suggested by various global environmental conventions. The present study was conducted with the purpose of assessing diversity and density of bird and woody species in some greenspaces of Delhi, the rapidly urbanizing capital of India. The landscape of Delhi consists of a broad spectrum of environments ranging from the city forests to highly modified artificial landscapes in certain parks. We assessed bird and woody vegetation in 20 m×50 m belt transects in each of the 19 randomly selected greenspaces of varying size. Results exhibit a negative relationship between the density of exotic woody species and bird diversity. Specifically, Prosopis juliflora – an exotic, which was the most abundant tree in our samples – exhibited a negative relationship with bird diversity. Principal component analysis (PCA) reveals that forest-preferring bird species increase with increasing greenspaces size, shrub diversity and shrub density. We conclude that maintaining larger greenspaces with high structural diversity may be effective in maintaining plant and bird diversity in the study area.     

Soundscapes reveal disturbance impacts: biophonic response to wildfire in the Sonoran Desert Sky Islands

Context

While remote sensing imagery is effective for quantifying land cover changes across large areas, its utility for directly assessing the response of animals to disturbance is limited. Soundscapes approaches—the recording and analysis of sounds in a landscape—could address this shortcoming.

Objectives

In 2011, a massive wildfire named “the Horseshoe 2 Burn” occurred in the Chiricahua National Monument, Arizona, USA. We evaluated the impact of this wildfire on acoustic activity of animal communities.

Methods

In 2013, soundscape recordings were collected over 9 months in 12 burned and 12 non-burned sites in four ecological systems. The seasonal and diel biological acoustic activity were described using the “Bioacoustic Index”, a detailed aural analysis of sound sources, and a new tool called “Sonic Timelapse Builder” (STLB).

Results

Seasonal biophony phenology showed a diurnal peak in June and a nocturnal peak in October in all ecological systems. On June mornings, acoustic activity was lower at burned than at non-burned sites in three of four ecological systems, due to a decreased abundance of cicadas directly impacted by the death of trees. Aural analyses revealed that 55% of recordings from non-burned sites contained insect sounds compared to 18% from burned sites. On October nights, orthopteran activity was more prevalent at some burned sites, possibly due to post-fire emergence of herbaceous.

Conclusions

Soundscape approaches can help address long-term conservation issues involving the responses of animal communities to wildfire. Acoustic methods can serve as a valuable complement to remote sensing for disturbance-based landscape management.