Do regional gradients in land-use influence richness, composition and turnover of bird assemblages in small woods?
Introduction
Throughout the world, small areas of natural or semi-natural habitat have an important role in maintaining biodiversity in human-dominated environments (Saunders et al., 1987; Forman, 1995; Laurance and Bierregard, 1997). Consequently, much attention has been given to identifying factors that influence the conservation value of such areas. Many studies have described relationships between the number of animal species, or occurrence of particular species, and attributes of habitat patches such as their size, shape, habitat diversity and management history (Freemark and Merriam, 1986; Bennett, 1987; Loyn, 1987; Bolger et al., 1997; Deacon and Mac Nally, 1998). The location of patches in relation to other suitable habitat has also been identified as a significant influence. Thus, features such as the distance to potential source populations (Opdam et al., 1985; Newmark, 1991; Thomas and Jones, 1993), the amount of nearby similar habitat (Askins et al., 1987; Jansson and Angelstam, 1999; Graham and Blake, 2001), and the presence of linking habitats (Bright et al., 1994; Haas, 1995) have been shown to complement patch-level characteristics as influences on the distribution of animal species.
The growing recognition of the importance of landscape context (e.g. Wiens, 2002; Wiens et al., 2002) has led to closer scrutiny of the structure of landscapes within which habitat patches are located. It is not only similar areas of habitat that may be important influences, but also the composition and spatial arrangement of other land-uses of differing quality for the biota (e.g. urban areas, roads, wetlands, arable land). Increasing attention is being given to the extent to which the overall structure of the landscape may influence the status of populations and communities (Pearson, 1993; Bennett and Ford, 1997; Fuller et al., 1997; Baillie et al., 2000; Pope et al., 2000; Soderstrom and Part, 2000; Bellamy et al., 2003). Indeed, it has been suggested (Diamond et al., 1987; Saunders et al., 1991; Hobbs, 1993) that processes operating in the wider landscape or regional land mosaic may ultimately have as great, or greater, influence on the composition and status of the biota in small patches than within-patch processes. First, surrounding land-uses can modify the dynamics of metapopulations by influencing the capacity of species to disperse through the landscape. Different forms and intensities of land-use offer different levels of ‘resistance’ to the movements of species (Laurance, 1991; Gascon et al., 1999; Lindenmayer et al., 2002). Second, particular land-uses may offer additional food, shelter or other resources that complement those available to species within habitat patches (Pope et al., 2000). Third, other plant and animal species or disturbance processes associated with surrounding land-uses can have a marked impact on habitat quality in isolated patches (Saunders et al., 1991). There may be invasion or degradation of natural habitats (Hobbs, 1993; Scougall et al., 1993; Abensperg-Traun et al., 1996), or the imposition of new predators and competitors that result in population declines or change in the structure of assemblages (Andrén, 1992; Grey et al., 1998).
Therefore, one expects that habitat patches of similar size or vegetation type will show differences in their biotic communities depending on the context of the patch in relation to patterns of land-use and the physical environment. Of course, different species will respond to landscape context in different ways and at different scales. A number of studies have detected context effects by testing the influence of habitat availability within a defined radius of a patch, on the occurrence or richness of species within that resource patch (Brennan et al., 2002). The scale for such studies has often been ⩽1 km (e.g. Pearson, 1993; Jansson and Angelstam, 1999; Soderstrom and Part, 2000; Graham and Blake, 2001), a relatively small distance when studying a mobile taxon such as birds. Context effects have seldom been tested over a larger landscape scale (e.g. 1–10 km) or in relation to environmental variation and land use across the entire region in which study sites are located.
In this study we examine the potential effect of regional context on assemblages of breeding birds in small woods in south-eastern England. Previous work in this study area showed that the richness of breeding bird species (Bellamy et al., 1996a) and the distribution of individual species (Hinsley et al., 1995a) are influenced both by the characteristics of woods in which birds nest and habitat attributes in the surrounding landscape. Distances of up to 1 km radius around woods were used to assess features such as woodland cover and length of hedgerows. The various types of responses to landscapes in the region suggested that species are making different sets of choices between large-scale habitat factors and fine-scale selection of sites for breeding (Hinsley et al., 1995b). Choices at larger scales appear to be important for some species. For example, analysis of the distribution of the nuthatch Sitta europaea (Bellamy et al., 1998) indicated the importance of variation in woodland cover between regions in southern England. Consequently, in this paper we use data pertaining to land-use and the physical environment to identify regional environmental gradients across a 2100 km2 region, independently of the locations of woods where birds were censused. We then examine three aspects of breeding assemblages in woods – species richness, relative species turnover and composition – to explore the extent to which the context of a wood in relation to these regional gradients influences the status of its bird assemblage. The implications of regional context effects for the conservation of biota are then discussed.
Section snippets
Study area
The study was carried out in south-east England in a region of 2100 km2 (70 km × 30 km) in the counties of Cambridgeshire and Lincolnshire (Fig. 1). Two main landform types occur in the region: flat expanses of drained fenland in the east and more-undulating countryside of heavy clays in the south-west. Land-use throughout the region is dominated by intensive arable farming, with the main crops being autumn-sown cereals (barley, wheat), oilseed rape, sugar beet and potatoes. Towns and numerous
Variation in breeding bird assemblages among woods
Data on species richness, species turnover and the composition of breeding bird assemblages were calculated for 88 woods ranging from 0.5 to 29.9 ha in area. Most woods were small; the mean size was 2.8 ha and only 16% (14/88) were larger than 5 ha. A total of 49 species was recorded breeding in these woods during the study (Table 1). The 3-year means for the number of species per wood ranged from 5 to 24, with an overall mean of 12.6 species.
Six species of migrants primarily depend on woodland
Discussion
A fundamental principle in landscape ecology is that ‘landscape context matters’. This is not only relevant to conceptual development in the discipline (e.g. Forman, 1995; Wiens, 1995) but is of great practical importance for the conservation of biodiversity in human-dominated environments. Many species now occupy patches of habitat within heavily modified land mosaics in which the composition and configuration of habitats differ markedly from the natural state. Likewise, many small
Acknowledgements
This research was initiated while AFB was on study leave at Centre for Ecology and Hydrology, Monks Wood. He thanks Dr. Barry Wyatt for the use of facilities at Monks Wood, the School of Ecology and Environment, Deakin University for study leave, and Land and Water Australia for a Travelling Fellowship that assisted with travel costs. We thank Gary Luck and Jim Radford for their comments on the manuscript. Thanks also to all the landowners, managers and keepers who allowed access to their land.
References (66)
- et al.
Relationship between regional abundance of forest and the composition of forest bird communities
Biological Conservation
(1987) - et al.
Importance of area and habitat heterogeneity to bird assemblages in temperate forest fragments
Biological Conservation
(1986) - et al.
Matrix habitat and species richness in tropical forest remnants
Biological Conservation
(1999) - et al.
The influence of hedge structure, management and landscape context on the value of hedgerows to birds: a review
Journal of Environmental Management
(2000) Effects of landscape fragmentation on ecosystem processes in the Western Australian wheatbelt
Biological Conservation
(1993)- et al.
Bird communities in small woods in an agricultural landscape: effects of area and isolation
Biological Conservation
(1985) Consequences of forest fragmentation for the dynamics of bird populations: conceptual issues and the evidence
- et al.
The effects of habitat fragmentation and livestock-grazing on animal communities in remnants of gimlet Eucalyptus salubris woodland in the Western Australian wheatbelt. I. Arthropods
Journal of Applied Ecology
(1996) Corvid density and nest predation in relation to forest fragmentation: a landscape perspective
Ecology
(1992)- et al.
Consequences of large-scale processes for the conservation of bird populations
Journal of Applied Ecology
(2000)
Factors influencing bird species numbers in small woods in south-east England
Journal of Applied Ecology
Local extinctions and recolonisations of passerine bird populations in small woods
Oecologia
Synchrony of woodland bird populations: the effect of landscape structure
Ecography
Variation in the relationship between numbers of breeding pairs and woodland area for passerines in fragmented habitat
Ecography
The influences of habitat, landscape structure and climate on local distribution patterns of the nuthatch (Sitta europaea L.)
Oecologia
Conservation of mammals within a fragmented forest environment: the contributions of insular biogeography and autecology
Linkages in the Landscape. The Role of Corridors and Connectivity in Wildlife Conservation
Land use, habitat change and the conservation of birds in fragmented rural environments: a landscape perspective from the Northern Plains, Victoria, Australia
Pacific Conservation Biology
Response of rodents to habitat fragmentation in coastal southern California
Ecological Applications
Focal patch landscape studies for wildlife management: optimizing sampling effort across scales
Dormouse distribution: survey techniques, insular ecology and selection of sites for conservation
Journal of Applied Ecology
Hierarchical partitioning
The American Statistician
PRIMER v5
Local extinction and nestedness of small-mammal faunas in fragmented forest of central Victoria, Australia
Pacific Conservation Biology
Bird survival in an isolated Javan woodland: island or mirror
Conservation Biology
Deciduous forest and resident birds: the problem of fragmentation within a coniferous forest landscape
Landscape Ecology
Land Mosaics. The Ecology of Landscapes and Regions
Estimate of the area affected ecologically by the road system in the United States
Conservation Biology
Landscape composition models for breeding bird populations in lowland English farmland over a 20 year period
Ecography
The Land Cover Map of Great Britain: an automated classification of Landsat Thematic Mapper data
Photogrammetric Engineering & Remote Sensing
Influence of patch- and landscape-level factors on bird assemblages in a fragmented tropical landscape
Ecological Applications
The distribution of passerine birds in hedgerows during the breeding season in relation to characteristics of the hedgerow and adjacent farmland
Journal of Applied Ecology
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