Using ecoacoustics to assess the biodiversity value of woodland creation sites

Expanding woodland cover is the focus of many restoration efforts because of its potential to aid biodiversity recovery and mitigate climate change. In the UK, woodland creation schemes have contributed to increasing woodland cover from a historic low of 5% in the early 1900s to the current figure of 13%, and the UK Government has pledged to plant an additional 30,000 ha of trees per year up to 2050. However, we know surprisingly little about the ecological consequences of creating and restoring woodlands over large spatial and temporal scales. The lack of empirical studies comes partly from the challenges associated with studying landscapes over ecologically meaningful scales (e.g. to account for time lags in species colonisation and capitalisation of resources in new habitat patches). These challenges are particularly pronounced for habitats with slow development rates and of important conservation concern, such as woodlands.

Tree planting has been the most common woodland expansion strategy in the UK for many decades, but this approach is increasingly questioned following overestimates of benefits, poor targeting and challenges in scaling-up at the level required to meet ambitious woodland expansion targets. As a result, there is growing interest in incorporating ‘natural colonisation’ (allowing trees to colonise new areas naturally, often as a component of ‘rewilding’) into woodland expansion strategies, partly because it is assumed that naturally created woodlands will be more structurally diverse, ecologically complex and resilient than planted sites [1]. But much of the evidence on natural colonisation is drawn from regions with quicker habitat succession rates (e.g. the tropics) and where landscapes have not been as heavily degraded as in the UK, and it’s unclear how applicable this is to temperate regions. We thus still lack relevant evidence on the relative merit of these alternative approaches to woodland creation.

Ecoacoustics is an emerging and fast evolving field that investigates natural and anthropogenic sounds and their relationships with the environment [2]. The acoustic environment or “soundscape” can be quantitatively described using indices aimed at characterising acoustic diversity in space and time through the incidence, abundance and features of sounds [3]. As animal vocalisations are often unique in their acoustic features, acoustic indices can be used to infer community diversity and detect shifts in faunal communities of acoustically active species. For example, avian acoustic indices correlate strongly with bird species richness in temperate regions [4].

This project will use ecoacoustics to investigate temporal changes in the soundscapes of woodland creation sites. Specific questions to address may include:

1) How do woodland soundscapes change over time in woodland creation sites? For example, do woodlands gradually acquire a larger diversity of biotic sounds (and species) as they mature?
2) How do woodland characteristics (e.g. woodland amount and connectivity in the surrounding landscape, after controlling for patch size and vegetation structure) influence the soundscapes of woodland creation sites?
3) How does woodland creation method (e.g. planting or natural colonisation) influence the trajectory of woodland soundscapes over time? For example, do planted woodlands acquire more complex soundscapes quicker than naturally colonised woodlands?
4) Does acoustic diversity correlate positively with the species richness of acoustically active taxa in woodland creation sites? If so, are acoustic indices potentially useful proxies for the biodiversity value of woodland creation sites?

Click on an image to expand

Image Captions

Woodland creation site planted on former agricultural land in the 1960s (photo Kevin Watts)


This project will capitalise on an existing network of sites which form part of the Woodland Creation and Ecological Networks (WrEN) project, a large-scale natural experiment designed to study the long-term effects (up to 160 years) of woodland creation on biodiversity and ecosystem functioning in UK landscapes [5] (www.wren-project.com). As part of WrEN, more than 100 woodland sites planted on former agricultural land have been surveyed using standard techniques for a range of taxonomic groups, including vocalising animals such as birds, bats and small mammals [6-8]. Additionally, a subset of these sites (n=35) has been intensively surveyed using acoustic recorders, but the majority of these data remain unprocessed and would be available for the student to analyse. There is also scope for the student to collect additional data using full-spectrum acoustic recorders (e.g. AudioMoths) to characterise the audible and ultrasonic soundscapes of a larger number of woodland sites created in recent decades using a combination of tree planting and natural colonisation approaches (part of the TreE_PlaNat project). The student will derive a range of acoustic indices (e.g. Acoustic Complexity Index) to infer biotic community diversity and sub-sample from recordings to quantify the occurrence of key woodland species with characteristic vocalisations, potentially utilising semi-automated approaches such as machine learning.

Project Timeline

Year 1

Literature review; training in experimental design and acoustic monitoring techniques; initial analysis of existing acoustic dataset (e.g. deriving acoustic indices).

Year 2

Fieldwork to collect additional acoustic data; further analysis of acoustic dataset (e.g. quantifying the occurrence of individual species).

Year 3

Data processing and analysis; paper and thesis write-up.

Year 3.5

Paper and thesis write-up.

& Skills

The PhD will be based at Stirling and the student will visit Forest Research (Edinburgh) and Newcastle University to meet with co-supervisors and other researchers for seminars and specific training. Training and skills will include:
1) Fieldwork and experimental design. Training in the required field skills (e.g. woodland surveying, acoustic monitoring), and sampling design.
2) Numeracy, data analysis, ecological modelling and informatics. These skills will be mainly gained through targeted training courses within the IAPETUS consortium (e.g. Programming and Analysis of Environmental Data in R).
3) Land-use policy and management; the student will gain insights into understanding and formulating policy relevant research questions, skills for interdisciplinary research and the process of translating research into guidance and advice, working closely with CASE partner Forest Research.
4) Complementary training in transferable skills. Training in core scientific skills (data management, presentations, paper writing).

References & further reading

[1] Woodland Trust (2020) Emergency Tree Plan for the UK – How to Increase Tree Cover and Address the Nature and Climate Emergency. [2] Sueur J & Farina A (2015) Ecoacoustics: the Ecological Investigation and Interpretation of Environmental Sound. Biosemiotics 8, 493–502. [3] Sueur J et al. (2014) Acoustic Indices for Biodiversity Assessment and Landscape Investigation. Acta Acustica united with Acustica 100, 772–781. [4] Eldridge A et al. (2018) Sounding out ecoacoustic metrics: Avian species richness is predicted by acoustic indices in temperate but not tropical habitats. Ecological Indicators 95, 939–952. [5] Watts K et al. (2016) Using historic woodland creation to construct a long-term, large-scale natural experiment: The WrEN project. Ecology & Evolution 6: 3012- 3023. [6] Whytock RC et al. (2018) Bird community responses to habitat creation in a long-term, large-scale natural experiment. Conservation Biology 32, 345-354. [7] Fuentes-Montemayor E et al. (2017) Species mobility and landscape context determine the importance of local and landscape-level attributes. Ecological Applications 5, 1541–1554. [8] Fuentes-Montemayor E et al. (2020) Small mammal responses to long-term large-scale woodland creation: the influence of local and landscape-level attributes. Ecological Applications 30, e02028.

Apply Now