Exploring the relationships between landscape structure and woodland biodiversity within the lowland agricultural matrix of central-southern England

Today, much of lowland England is characterized by fragments of native woodland existing within a larger agricultural matrix, a result of intensive farming and landscape modification (Hinsley et al., 1995; Fournier & Loreau, 1999). This poses a serious threat to woodland biodiversity with many species groups having declined. This trend is mirrored across Europe (Dauber et al., 2003; Hendrickx et al., 2007).

UK studies have highlighted the benefits of key landscape elements such as hedgerows and headlands, but there is limited published work focusing on the entire matrix at a counties-wide scale (Green et al., 1994; Gardiner, 2007). Understanding how woodland communities respond to the wider landscape is essential if we are to manage landscapes and habitats in a way that allows us to maintain and develop functioning ecological networks for biodiversity. This comes at a time when land-use demands are increasing and people are seeking guidance on the most effective ways to enhance wildlife within agricultural landscapes without compromising on other land-use requirements.

We investigated the effect of landscape composition and structure on woodland species communities across the agricultural lowlands of southern England in 2011. Real-time carabid beetle and bird data were collected from 57 woodland sites to provide the most accurate representation of species occurrence. Landscape variables from the 4 square kilometres surrounding each sample woodland were compiled in a Geographic Information System using up-to-date high resolution spatial data coupled with ground truthing. These included matrix composition and indices of heterogeneity and connectivity, obtained using Fragstats 4.1 (McGarigal & Ene, 2012). Canonical Correspondence Analyses (Canoco 5) were used to analyse the effects of landscape predictors on both taxonomic groups.

Significant predictors positively influencing community composition of carabids included the presence of scrub and water bodies in the matrix and connectivity provided by mature, intact hedgerows (p=0.008), particularly between small wood patches. Negative effects on carabids were related to increased arable landcover (p=0.008). Roads, which act as a fragmenting barrier within the landscape were associated with a decrease in carabid abundance (p=0.014), particularly for large, woodland species with low dispersal power (Aviron et al., 2005).

For bird assemblages, no individual habitat components within the matrix could be identified as significant. We divided assemblages into subgroups based on habitat requirements and families: there was some evidence that species with distinct habitat predilections responded to the extent of preferred elements in the matrix e.g. coal tit (Periparus ater) and coniferous woodland. Connecting hedgerows between wood patches and through the matrix were not significant, nor was an increase in matrix heterogeneity which contrasts with other bird-landscape research (Barbaro et al., 2007; Haslem and Bennett, 2008). Alike to other studies, greater bird species richness was observed in larger woodlands, although the result was not statistically significant (p=0.077).

We suggest that using multiple taxonomic groups which differ in their migratory ability and habitat requirements is essential for understanding complex species-landscape interactions (Dauber et al., 2003; Barbaro et al., 2007). Our results indicate that a well-connected landscape to facilitate long-term movement of species is beneficial to carabids, and we support the need for heterogeneous landscapes based on previous research, despite a lack of significance for the bird data in our study. We firmly advocate that identifying specific matrix elements such as scrub, hedges and water bodies is directly relevant to the current options available under agri-environment schemes, and can help with the development of ecological networks in woodland-agricultural environments.