Does rewilding improve ecosystem resilience?: a soundscape perspective

Understanding why some ecosystems appear more resilient to perturbation than others is of fundamental importance if we wish to avoid biodiversity collapse and maintain a habitable planet.

There is a rapidly growing shift towards low intensity, large scale, semi-passive restoration approaches, such as rewilding, that seek to restore ecological processes rather than deliver pre-defined structure-based outcomes. Within the overall context of rewilding harnessing the restorative power of beavers through their habitat engineering activities is becoming increasingly commonplace in Britain, with most English counties now having enclosed beaver projects either planned or in operation, a situation unimaginable a decade ago. In Scotland Eurasian beavers have occurred again in the wild for about 20 years with their population now approaching 2000 animals and with plans to translocate them more widely. The ecological benefits that stem from dam building and the other engineering activities of beavers are, in some senses, well established, with a catalogue of studies demonstrating increases in birds, plants, amphibians, invertebrates and bats [1]. These complement the ability of beaver ponds to intercept pollutants and improve downstream water quality, attenuate flow peaks and mitigate the disturbance effects of drought and wildfires [2]. However, the picture is incomplete since many indicator biological taxa are studied in isolation while the benefits of beavers most likely do not accrue evenly and are sensitive to the surrounding landscape matrix. The degree of subsidy from aquatic to terrestrial systems and how this varies in relation to beaver activity, also remains poorly understood, despite its potential importance to higher trophic levels when other resources are depleted [3]. Finally, although beaver ponds seem to provide a stabilising influence in the face of extreme events, it is unknown whether there is an accompanying ecological benefit in terms of enhanced resilience of populations, communities or ecosystem functions. The solution to some of these questions has remained elusive in part because traditional monitoring approaches are invasive and costly and therefore cannot be deployed at the spatial and temporal frequency that is desirable.

Here we will apply a novel soundscape perspective using passive acoustic monitors to address the following objectives:

1. Explore lateral spillover effects from wetlands into the surrounding terrestrial habitat using bioacoustics data collection (focussing on birds and bats), contrasting beaver-engineered systems with un-engineered (control) streams and ponds.
2. Test the complementary value of the aquatic soundscape for characterising small wetlands and their relative habitat complexity and the consistency between ecoacoustics evidence and that yielded by traditional sampling approaches.
3. Determine if there are differences in temporal stability or recovery rate of ecoacoustic indicators in beaver engineered and control systems in relation to the timing of environmental shocks and the landscape context in which these occur.

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Image Captions

Typical beaver engineered wetland habitat at the study site


Our project exploits the emerging and fast evolving field of ecoacoustics which investigates natural and anthropogenic sounds and their relationships with the environment [4]. The acoustic environment or “soundscape” can be quantitatively described using indices designed to characterise acoustic diversity in space and time through the incidence, abundance and features of sounds. As animal vocalisations are often unique in their acoustic properties, acoustic indices can offer a proxy for community diversity or detect shifts in faunal communities of acoustically active species. For example, avian acoustic indices correlate strongly with bird species richness in temperate regions [5]. Over recent years there has also been increasing interest in the application of ecoacoustics to freshwater monitoring as an alternative to traditional invasive and time-costly approaches whose spatial and temporal reach is often limited [6].

This project exploits the unique opportunities presented by a demonstration project on the use of beavers in wetland restoration which we have been monitoring for over 20 years in close cooperation with the landowner. The focal estate in Perthshire covers a typical range of agricultural and woodland land uses. It also contains the highest density of beaver dams in the UK, following the release of animals in 2002. Landscape change has been tracked since this time [7]. Since 2021, in a move towards more landscape scale rewilding, beavers have been complemented by low density conservation grazing using free-ranging cattle, ponies and pigs, with all sheep being removed and crop cultivation ceasing. A range of conventional agricultural landuse matrices exist nearby providing the opportunity to assess the context dependency of beaver influence. The study site is extensively instrumented and the project can draw on a wealth of supporting data and knowledge assembled via our long-term research and a succession of past and ongoing PhD studentships.

For Obj 1 the primary interest is in the extent to which the benefits of beaver ponds ‘spillover’ into surrounding habitats, for example, through the supply of emerging insect prey to terrestrial avian predators. The emphasis will be on testing the lateral distance decay of any such effect, its sensitivity to the surrounding landuse matrix (semi natural vs agricultural) and the extent to which the spillover from wetlands engineered by beavers differs from other streams and ponds in the landscape. We will identify 3-5 replicate examples of the key wetland habitat types in different matrices and deploy passive recorders at two distances away from the water’s edge. This work will benefit from independent studies quantifying aquatic insect emergence and distance decay in predatory ground-dwelling arthropods. For Obj 2 we will test if passive acoustic monitors reveal a distinct soundscape signature of beaver-engineered wetlands (e.g. beaver ponds compared to other pre-existing pond types) and if the evidence in relation to fish, amphibians and selected invertebrates such as water beetles is consistent with observations and pre-existing data derived recently using traditional approaches. We will also assess if the aquatic soundscape can offer a guide to the degree of terrestrial spillover. Finally (Obj 3), based on insights from Obj 1 and Obj 2 we will use selected ecoacoustics indicators from the terrestrial and aquatic soundscapes at a subset of sites and explore how these change over time in relation to extreme events such as flood and drought events. Specifically, we will assess if the pattern of change in the soundscape pre- and post-disturbance provides any evidence that habitat engineering by beavers can boost ecological resilience.

Project Timeline

Year 1

Literature review; introduction to study sites and site managers, learn passive acoustic sampling methods and plan sampling design for Obj1 and Obj 2; stakeholder liaison, training needs assessment (e.g. statistical or identification courses). Implement sampling regime.

Year 2

Ongoing sampling campaign. training course on analysis of bioacoustics data, processing of acoustic recorders, integration with existing data. Advanced statistical training. UK workshop/conference presentation of interim findings. Outreach to build support for project. Draft paper 1.

Year 3

Opportunistic sampling, time series exploration for Obj 3, analysis and interpretation of full dataset. Integration of additional external datasets. Draft paper 2. Present at national conference.

Year 3.5

Thesis writing. International conference attendance to present results. Briefings on key findings for non-academic audience. Viva training.

& Skills

The student will benefit from training covering a mix of field, lab and advanced analytical skills including processing and analysis of bioacoustics data. Development will be further supported through IAPETUS specific provision and external courses. Example courses include; statistical analysis with R, media training; insights to industry; leadership skills; conference skills (e.g., networking, poster and oral presentation skills); Geographic Information Systems; grant writing. The research findings will be published as journal articles led by the research student in leading ecology journals. Given the strong public and stakeholder interest in beavers and rewilding more generally we expect that such articles will attract a high media interest. The student will also present results at conferences including the Scottish Ecology, Environment and Conservation Student Conference, British Ecological Society annual conference, as well as to local and regional stakeholder for a and special interest groups to bring the project to a wider audience. The student will benefit from inclusive and productive lab groups and PhD cohorts at Stirling and Newcastle and will have the opportunity to engage with related large research projects at both institutions.

References & further reading

[1] Stringer, A.P. and Gaywood, M.J. (2016), The impacts of beavers Castor spp. on biodiversity and the ecological basis for their reintroduction to Scotland, UK. Mammal Review 46, 270-283. https://doi.org/10.1111/mam.12068

[2] Law A, McLean F & Willby N (2016) Habitat engineering by beaver benefits aquatic biodiversity and ecosystem processes in agricultural streams. Freshwater Biology, 61, 486-499. https://doi.org/10.1111/fwb.12721

[3] Lewis-Phillips, J; Brooks, SJ; Sayer, CD; Patmore, IR; Hilton, G; Harrison, A; Robson, H; (2020) Ponds as insect chimneys: restoring overgrown farmland ponds benefits birds through elevated productivity of emerging aquatic insects. Biological Conservation, 241, Article 108253. https://doi.org/10.1016/j.biocon.2019.108253

[4] Sueur, J., Farina, A. Ecoacoustics: the Ecological Investigation and Interpretation of Environmental Sound. Biosemiotics 8, 493–502 (2015). https://doi.org/10.1007/s12304-015-9248-x

[5] Alcocer, I., Lima, H., Sugai, L. S. M., & Llusia, D. (2022). Acoustic indices as proxies for biodiversity: a meta-analysis. Biological Reviews. https://doi.org/10.1111/BRV.12890

[6] Abrahams, C., Desjonquères, C., & Greenhalgh, J. (2021). Pond Acoustic Sampling Scheme: A draft protocol for rapid acoustic data collection in small waterbodies. Ecology and Evolution, 11, 7532–7543. https://doi.org/10.1002/ECE3.7585

[7] Law A, Gaywood MJ, Jones KC, Ramsay P & Willby NJ (2017) Using ecosystem engineers as tools in habitat restoration and rewilding: beaver and wetlands. Science of the Total Environment, 605-606, 1021-1030. https://doi.org/10.1016/j.scitotenv.2017.06.173

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