© Marcel Burkhardt
Vickery, J. & R. Arlettaz (2012)
The importance of habitat heterogeneity at multiple scales for birds in European agricultural landscapes.
in Birds and Habitat: Relationship in Changing Landscapes, Chapter 7: 177–204
Farmland throughout the world is frequently likened to a mosaic or patchwork and this heterogeneity is widely recognised as strongly influencing the abundance and diversity of species that these landscapes support. Globally, modern intensive agriculture has greatly reduced this ‘patchiness’ at a range of spatial and temporal scales. This change has been particularly well documented in temperate Europe (Benton et al., 2003; Ba´ ldi et al., 2005; Roschewitz et al., 2005; Wretenberg et al., 2006; Stoate et al., 2009). The fine-grained, diverse habitat mosaic, typical of much ‘traditional agriculture’, has become increasingly uniform under modern agricultural management. This reduction in habitat complexity has been linked, at least in part, to declines in farmland biodiversity, including plants and invertebrates (Smart et al., 2000; Sotherton and Self, 2000; Oliver et al., 2010), mammals (Smith et al., 2005) and birds (Donald et al., 2001a; Benton et al., 2003; Wilson et al., 2005). In general, the more habitat elements a farmed landscape contains, the wider the range of resources on offer and the higher the diversity and abundance of organisms supported. This may be due, in part, simply to the increased likelihood of a given farmed landscape containing a key habitat type (Heikkinen et al., 2004). However, many species require a diversity of resources to complete their life cycle. At its most basic, birds require two essential resources: a suitable nest site and sufficient food throughout the year. These basic nesting and foraging requirements often vary within and between seasons. Bird-rich farmland should provide safe foraging habitats, offering abundant and accessible food in relatively close proximity to suitable cover for nesting and/or protection from predators or harsh weather. The extent to which farmland birds require a diverse landscape matrix, containing both semi-natural and cultivated habitat components, is illustrated by many examples in the following sections. This chapter focuses on the importance of heterogeneity in the context of the requirements of individual species, rather than farmland bird communities as a whole.Wedemonstrate that avian life histories, even the simplest ones, require access to a broad range of resources over spatial and temporal gradients and we show how this is more likely to be delivered by a heterogeneous than a homogeneous landscape. Since this heterogeneity is scale-dependent, we examine bird requirements for, and responses to, heterogeneity at three scales: within fields (e.g. swards), between fields or at the farm scale (in cropped and noncropped habitats), and at the landscape scale (between farms). We then briefly consider some approaches that could restore heterogeneity in areas where it has been reduced by intensive agriculture and the ways in which such restoration may benefit wider biodiversity and some key ecosystem services. There are several caveats that should be made at the outset. First, we provide a broad overview of the importance of heterogeneity at different scales, rather than a comprehensive review. Second, the text has a temperate and lowland northwest European bias, since this is where the majority of the work has been undertaken and these are the systems with which we are most familiar. We acknowledge that patterns and processes may not be generic across all regions, particularly between the more intensively managed landscapes of northwest Europe and those of south and east Europe (Reif et al., 2008; Erdo¨ s et al., 2009; Stoate et al., 2009; Bata´ry et al., 2011a). Third, the distinctions between field, farm and landscape scale are not always clear cut, particularly at the farm and landscape scales. The issue of scale is further complicated by the fact that, while quantifying environmental heterogeneity depends on the scale of measurement, an organism’s response to it actually depends on its perception of the environment, something that remains poorly understood and will vary between species (Wiens, 1989).