Spatial heterogeneity and farmland birds: different perspectives in Western and Eastern Europe

Abstract

One of the most dramatic declines of biodiversity in Europe has been the collapse of farmland bird populations (Donald et al. 2006). The loss of habitat heterogeneity is suggested as being an important driver behind this loss, and operates at a range of spatial scales from specialization of land-use on farms and across farmed landscapes to the disappearance of hedgerows and fallows and the homogenization of crop sward structure (Benton et al. 2003). Most of our knowledge of agricultural practices and farmland bird ecology, however, is from a few countries only, with 76% of papers in the Web of Science originating from the UK, France, Netherlands, Spain, Germany and Sweden, and less than 10% from Central and Eastern European countries (Donald et al. 2002, Kleijn & Baldi 2005, paper numbers are from a search on the Web of Science from 1975 to 28 August 2010 for ‘(‘agricultur*’ OR farmland) AND (‘species richness’ OR biodivers*) AND bird*’). Common features of most of these Western countries are the severe long-term decline of farmland bird populations and high levels of agricultural intensification (use of agrochemicals, mechanization, etc.). Most Central and Eastern European countries (CEECs) experience different biogeographical and climatic conditions, and have different economic and agricultural conditions with recent entry to the EU and the application of the Common Agricultural Policy, and a change from a socialist to market-regulated economy in the 1990s. Therefore, most of the knowledge on farmland bird ecology only partially covers the variation in farming systems, bird population status, biogeographical conditions and socioeconomic background across Europe. Inevitably, any generalization based on this biased knowledge may be misleading (Kleijn & Baldi 2005, Whittingham et al. 2007). We highlight a potential problem if research evidence were to be generalized across different parts of Europe to guide conservation strategies, for example by applying knowledge of farmland bird ecology in Western Europe to the CEECs. We focus on farmland heterogeneity as an example because this is delivered by a wide range of management options in agri-environment schemes (AES) designed to reverse biodiversity losses. These include the creation and maintenance of hedgerows, beetle banks or field margins. Many studies have indicated a positive correlation between species richness or abundance of farmland birds and landscape heterogeneity (Benton et al. 2003), but these results were based mostly on Western European evidence, and a critical evaluation of the impact of farmland heterogeneity across European farmland systems is still missing. Indeed, there is an increasing interest in the topic recently due to several still open questions, of which geographical restriction is only one (Batary et al. 2011, Fahrig et al. 2011, Pickett & Siriwardena in press). Heterogeneity of farmland has changed during the history of agriculture (e.g. Sutherland 2004). These changes include land conversions and shifts in landscape-level patterns. Therefore, heterogeneity should only be promoted if there is evidence that biodiversity loss stems from loss of previous heterogeneity. Many Western European grasslands, for example, were heavily homogenized in the 20th century, as stone walls and hedges were removed to create large, economically more profitable fields (Robinson & Sutherland 2002). However, in some cases the original landscapes may have been more homogeneous than the modern systems that have replaced them. In such cases, increasing heterogeneity may result in further habitat fragmentation, with harmful consequences to the original biodiversity (Fahrig 2003). Examples are large-scale semi-natural grassland systems in CEECs, such as the puszta grasslands in Hungary. These semi-natural grasslands cover more than 1 million hectares in Hungary and are the result of centuries of extensive livestock grazing. The baseline system is a vast open landscape with grasslands scattered with small wetlands, a few trees, woodlots and farms (Baldi et al. 2005). Accordingly, recent conservation management actions in these grassland landscapes aim to decrease heterogeneity, with the removal of structures such as lines of bushes in the pastures of Kiskunsag National Park (http://www.knp.hu), or hundreds of kilometres of drainage channels in the Hortobagy National Park (http://www.hnp.hu). There is therefore evidence of a beneficial role of homogeneous farmland landscapes from different areas of Europe. These include the nega*Corresponding author. Email: andrasbaldi@gmail.com