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Landscape Ecol (2018) 33:895–910 https://doi.org/10.1007/s10980-018-0639-7 RESEARCH ARTICLE Living on the edge: utilising lidar data to assess the importance of vegetation structure for avian diversity in fragmented woodlands and their edges M. Melin . S. A. Hinsley . R. K. Broughton . P. Bellamy . R. A. Hill Received: 24 December 2017 / Accepted: 26 March 2018 / Published online: 30 March 2018 Ó The Author(s) 2018 Abstract Objectives The aims were to examine the edge effect Context In agricultural landscapes, small woodland on bird diversity and abundance, and the contributory patches can be important wildlife refuges. Their value role of vegetation structure. Specifically: what is the in maintaining biodiversity may, however, be com- role of vegetation structure on edge effects, and which promised by isolation, and so knowledge about the edge structures support the greatest bird diversity? role of habitat structure is vital to understand the Methods Annual breeding bird census data for 28 drivers of diversity. This study examined how avian species were combined with airborne lidar data in diversity and abundance were related to habitat linear mixed models fitted separately at (i) the whole structure in four small woods in an agricultural wood level, and (ii) for the woodland edges only. landscape in eastern England. Results Despite relatively small woodland areas (4.9–9.4 ha), bird diversity increased significantly towards the edges, being driven in part by vegetation Data accessibility The lidar data used for this study is available from the Centre for Environmental Data Analysis at structure. At the whole woods level, diversity was http://www.ceda.ac.uk/. The bird data is owned and main- positively associated with increased vegetation above tained by the Centre of Ecology and Hydrology (https://www. 0.5 m and especially with increasing vegetation ceh.ac.uk/). M. Melin (&) Á R. A. Hill P. Bellamy Department of Life and Environmental Sciences, Center for Conservation Science, RSPB, The Royal Bournemouth University, Talbot Campus, Fern Barrow, Society for the Protection of Birds (RSPB), The Lodge, Poole, Dorset BH12 5BB, UK Sandy, Bedfordshire SG19 2DL, UK e-mail: [email protected] e-mail: [email protected] R. A. Hill e-mail: [email protected] S. A. Hinsley Á R. K. Broughton Centre for Ecology and Hydrology, Benson Lane, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK e-mail: [email protected] R. K. Broughton e-mail: [email protected] 123 896 Landscape Ecol (2018) 33:895–910 density in the understorey layer, which was more dispersal corridors for a range of species (Hinsley et al. abundant at the woodland edges. Diversity along the 1995; Fuller et al. 2001). Partly due to these reasons, edges was largely driven by the density of vegetation but also strongly influenced by vegetation structure below 4 m. (Fuller 1995; Bata´ry et al. 2014), higher densities of Conclusions The results demonstrate that bird diver- some bird species may be recorded at forest edges sity was maximised by a diverse vegetation structure (Schlossberg and King 2008; Knight et al. 2016). across the wood and especially a dense understorey The influence of vegetation structure across forest along the edge. These findings can assist bird conser- edges has been investigated using conventional field vation by guiding habitat management of remaining methods, such as ground-based vegetation and bird woodland patches. surveys, and more recently with remote sensing techniques. For example, in the Czech Republic, Keywords Avian diversity Á Fragmentation Á Hofmeister et al. (2017) assessed the role of fragment Vegetation structure Á Lidar Á Forest edge Á Habitat size, edge distance and tree species composition on structure Á Edge effect Á Biodiversity bird communities using aerial imagery and land cover maps and found that both distance to the woodland edge and tree species composition had significant effects for majority of common bird species. In Introduction Canada, Wilson et al. (2017) used high-resolution aerial imagery and documented positive relationships Habitat fragmentation has been shown to have nega- between the presence of linear woody features and tive impacts on species diversity across ecosystems bird diversity among the forest-edge communities (Donald et al. 2001; Mahood et al. 2012). A common (models including the linear woody features were example of a modern fragmented landscape is a ranked best). In contrast, Duro et al. (2014) found low mosaic of woodland patches scattered in an agricul- or moderate relationships between Landsat imagery tural matrix. In such settings, fragmentation reduces based predictors and patterns of bird diversity in an the total extent of habitat for woodland species, agricultural environment (R2 values between 0.28 and increases patch isolation, and alters the habitat quality 0.3 for Landsat TM predictors and avian beta and of individual patches, for example by changing the gamma diversity). Thus, the drivers of diversity in physical characteristics, including edge to interior fragmented woodlands, and especially in relation to ratios (Fuller 2012). Birds have been widely studied in edge habitat, may be too fine-scaled to be studied this context because of the correlation demonstrated without sufficient consideration of the structural between their diversity and overall biodiversity (Kati composition of vegetation. et al. 2004; Gregory and van Strien 2010). Much While field methods and remote sensing imagery previous work has shown direct effects of habitat are limited in their ability to estimate the three- fragmentation on bird distributions, abundance, diver- dimensional (3D) structure of vegetation, airborne sity and reproductive success (Hinsley et al. 1996; laser scanning (ALS), utilising light detection and Rodriguez et al. 2001; Turcotte and Desrochers 2003; ranging (lidar), is ideal for this. The first studies to use Hinsley et al. 2009). lidar to characterize wildlife habitats were conducted Bird diversity in fragmented woodland is influ- on songbirds in the UK (Hinsley et al. 2002; Hill et al. enced by the area, structure and composition of the 2004). Since then, the literature has grown consider- woods themselves and by the configuration of the ably with many reviews showing the usefulness of surrounding landscape (Opdam et al. 1985; Hinsley lidar data in wildlife studies across different land- et al. 1995; Fletcher et al. 2007). Woodland edge scapes (e.g., Bradbury et al. 2005; Vierling et al. 2008; habitat can provide resources such as nest sites for Davies and Asner 2014; Hill et al. 2014), and birds that typically forage in more open and agricul- investigating data fusion and specific metrics with tural landscapes (Benton et al. 2003; Fahrig et al. which lidar could assist in habitat modelling (Vogeler 2011; Wilson et al. 2017). In addition, the presence of and Cohen 2016). Recent bird studies using lidar have connecting landscape features such as hedgerows and assessed the effects of vegetation structure on plant, tree lines can offer additional habitat, cover and bird and butterfly species diversity (Zellweger et al. 123 Landscape Ecol (2018) 33:895–910 897 2017), on grouse broods in boreal forests (Melin et al. Lady’s Wood and Riddy Wood. The main differences 2016), and on habitat envelopes of individual forest between the four woods are related to their shape, area dwelling bird species (Vogeler et al. 2013; Hill and and growth-stage of the forest, with the vegetation at Hinsley 2015; Holbrook et al. 2015; Garabedian et al. Lady’s Wood being generally lower than in the other 2017). three. In Britain, Broughton et al. (2012) showed that All woods are located within 5–20 m above sea occupation of forest edge by Marsh Tits (Poecile level with no steep topography (e.g., hills, ridges, palustris) was lower than in the interior, which was ravines or other distinct topographical features) in the associated with differences in habitat structure as near vicinity. All the woods are similarly surrounded assessed using airborne lidar data. Aside from this by an agricultural matrix and other larger woods are single species study, the technology has yet to be fully located ca. 1200 m away. Individual ringed birds have applied to species communities in habitat refuges been noted to move between these woods and the within highly modified environments. This paper study woods, but there is no evidence for any combines airborne lidar data with breeding bird census systematic bias in such movements. data for four small, isolated woods within an agricul- tural landscape to: (1) quantify the edge effect on bird Bird data collection species diversity in each wood; (2) determine the role of vegetation structure in any edge effect and how this As part of a larger, long-term study, the woods were might vary between the woods; and (3) assess how surveyed annually in 2012–2015 to determine the edge structure could be managed to enhance bird abundance and distribution of their breeding bird diversity and abundance in small woods. populations. Each wood was visited four times per year from late March to late July. Visits started shortly after dawn and avoided weather conditions likely to Materials and methods depress bird activity (e.g., rain and strong winds). Birds were recorded using a spot mapping tech- Study area nique (Bibby et al. 1992) based on the Common Birds Census method of the British Trust for Ornithology The study was conducted in Cambridgeshire, eastern (Marchant 1983). Each wood was searched systemat- England (52°25019.300N, 0°11018.300W), where four ically using a route designed to encounter all breeding remnant patches of ancient woodland that once territories (Bellamy et al. 1996). Routes varied covered the area lie within ca. 8 km2 in a landscape between visits, but always included walking around dominated by intensive arable agriculture (Fig. 1). the perimeter. All birds seen or heard, and their The four woods comprise Riddy Wood (9.4 ha), activity, were recorded on a map of the wood and the Lady’s Wood (8.4 ha) Raveley Wood (7.2 ha) and mapped locations were later digitised into a GIS.

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