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