- Top of page
- Materials and methods
Agricultural intensification in the second half of the 20th century caused a dramatic loss of biodiversity in Europe and was one of the reasons for the introduction of agri-environment schemes in the early 1990s (European Communities 1985). Agri-environment schemes are payments to farmers and other landholders to address environmental problems or to promote the provision of environmental amenities (OECD 2003). Hence they compensate farmers financially for any loss of income associated with measures that aim to benefit the environment or biodiversity. Nevertheless, more than a decade after the introduction of agri-environment schemes, only a limited number of studies evaluating the ecological effectiveness of these schemes have been published (Kleijn & Sutherland 2003). These studies present contrasting results (Kleijn & Sutherland 2003): some report positive effects of agri-environment schemes on biodiversity (Herzog et al. 2005), others show no or even negative effects (Kleijn et al. 2001). However, the study design of the majority of these evaluation studies is inadequate to assess reliably the effectiveness of the schemes, and most of them are not found in the readily available scientific literature. Furthermore, most of the evaluation studies have measured biodiversity by focusing on only one group of organisms (Kleijn & Sutherland 2003).
Although Switzerland is not part of the European Union (EU), its agri-environmental policy has evolved in a similar way. Farmers have benefited from direct payments for ecological measures since the reform of agricultural policy in 1992 (Bundesrat 1992). In addition, since 1999 farmers can manage at least 7% of the farmland as so-called ecological compensation areas (ECA) in order to obtain a basic direct payment (Bundesrat 1998). As a consequence, in 2001 almost 9% of the total agricultural land in Switzerland was managed as ECA (Bundesamt für Landwirtschaft 2002). ECA consist of a variety of habitats, including traditional orchards, hedges and field margin strips. However, by far the most important ECA habitat is extensively managed hay meadows (ECA hay meadows). Two important management requirements on ECA hay meadows specify that the vegetation must be cut and removed at least once every year, but not before 15 June (or later depending on altitude and agricultural zone), and fertilizer applications are prohibited.
Higher biodiversity on ECA than on conventionally managed hay meadows has been taken for granted: first, because on ECA meadows reduced fertilization and late cutting dates generally lead to a higher plant species richness and evenness (Rajaniemi 2002; Jacquemyn, Brys & Hermy 2003; Zechmeister et al. 2003); secondly, because on conventionally managed meadows the steadily increasing management intensity decreases plant species diversity and simplifies vegetation structure, which may in turn lead to reduction in arthropod diversity (Hunter & Price 1992; Matson & Hunter 1992; Schläpfer & Schmid 1999). We do not know, however, whether the extensification measures prescribed by the ECA scheme are sufficient to bring back the species that have been lost during the years of intensification (Schmid 2002).
We were further interested in possible edge effects on species diversity. Edge effects may be created through a more extensive management in the meadow edge than in the meadow centre (Melman & Van Der Linden 1988). In addition, a positive edge effect on species diversity could be expected as a result of arthropods and plants spreading from species-rich meadow margins into the meadow (Dennis & Fry 1992; Marshall & Moonen 2002). Finally, we wanted to assess whether results about the effectiveness of the scheme can be extrapolated from one to several study sites. The overall aim of the study was to evaluate the effectiveness of the ECA scheme for the preservation of biodiversity on hay meadows. Specifically, we tested the following hypotheses: (i) biodiversity is higher on ECA hay meadows than on conventionally managed hay meadows; (ii) species richness is higher in the meadow edge compared with the meadow centre; (iii) agri-environment schemes have similar effects in different regions.
A paired sample approach of ECA and control hay meadows was used to decouple spatial environmental variation and between-treatment variation as much as possible. For example, spatial variation between fields in species richness may occur because of habitat heterogeneity (Benton, Vickery & Wilson 2003), species pool differences (Partel et al. 1996) and management history (Poschlod & Wallis De Vries 2002). Biodiversity was assessed by investigating the species richness and evenness of four different groups of organisms representing three distinct trophic levels: vascular plants, grasshoppers, wild bees and spiders. All four groups are potential indicators of grassland quality with regard to overall species diversity (Detzel 1998; Duelli & Obrist 1998; Tscharntke, Gathmann & Steffan-Dewenter 1998; Bell, Wheater & Cullen 2001; Jacquemyn, Brys & Hermy 2003; Jeanneret, Schüpbach & Luka 2003). If they demonstrate similar responses to ECA management, further assessments required by the new ECA quality-control regulations in Switzerland (Bundesrat 2001) could be restricted to only one or two groups.
- Top of page
- Materials and methods
The results confirm our first hypothesis, that species richness and evenness are generally higher on ECA hay meadows than on conventionally managed meadows. For plants this can be seen as an effect of lower fertilizer levels and later hay cutting on ECA hay meadows. The higher species richness of the two taxa at the second trophic level, bees and grasshoppers, can be interpreted as consequence of the greater diversity (richness and evenness) in plant food sources (Pfisterer, Diemer & Schmid 2003). The bottom-up effect of plant diversity on primary consumer diversity is further supported by the positive correlation of species richness between vascular plants and wild bees, and between vascular plants and grasshoppers, respectively. However, the ecological quality of the fields prior to the uptake of the scheme is unknown. It is possible that the less accessible and least productive sites, and therefore the most extensively managed, locations became ECA hay meadows. The more productive sites are likely to have remained conventionally managed (Kleijn & Sutherland 2003). Therefore, the positive effect of the agri-environment scheme on biodiversity might also be influenced by the baseline diversity prior to the ECA management.
The absence of an effect of ECA management on spider diversity and the lack of a significant correlation between plant diversity and spider diversity may be the result of the trophic difference between secondary consumers and primary producers (Pfisterer et al. 2005). An alternative explanation is that prey abundance and vegetation structure may be more relevant to spiders than plant species richness and prey diversity (Baines et al. 1998; Bell, Wheater & Cullen 2001). Indeed, the higher spider diversity in the meadow edge than in the centre of both ECA and conventionally managed meadows indicates that greater spider diversities can spill over from adjacent habitats. This is particularly true for habitats with richer vegetation structure such as uncut field margins and forest margins. However, it seems that species richness of spiders should not be used as an indicator for the quality of hay meadows with regard to ecological compensation.
The second hypothesis, that species richness is higher in the meadow edges compared with the meadow centres, was only confirmed for vascular plants and spiders. These results might be explained by spiders and plants spreading from species-rich meadow margins into the meadows (Dennis & Fry 1992; Marshall & Moonen 2002). In addition, more extensive management in the meadow edges (Melman & Van Der Linden 1988) might lead to a more diverse vegetation structure, which in turn is known to increase spider diversity (Bell, Wheater & Cullen 2001). Thus, it could be that the potentially more diverse vegetation structure in the meadow edges promotes more spider diversity than the current management restriction of the scheme. However, in contrast to the spiders, plant species richness in the centre of ECA hay meadows was higher than plant species richness in the edge of conventionally managed hay meadows. This may indicate that, for plants, the ECA hay meadows contribute more to the preservation of species richness than species-rich edges of conventionally managed meadows. Against our expectations, grasshoppers and bees showed no edge effect. It could be that our sampling method was inappropriate to detect differences within a meadow for these two highly mobile groups.
The third hypothesis, that ECA hay meadows are similarly effective in promoting biodiversity across sites, was confirmed among the three selected study regions for the species richness of all indicator groups except the grasshoppers. The significant interaction between management and region for the species richness of grasshoppers is probably a result of the generally low diversity levels at one of the three study sites, Ruswil (Fig. 1). This finding should be taken as a cautionary note that regional factors such as site conditions (Benton, Vickery & Wilson 2003), species pool (Partel et al. 1996) and management history (Poschlod & Wallis De Vries 2002) can sometimes confound the measured effectiveness of agri-environment schemes. Therefore, it might be necessary to adjust the schemes to compensate for these factors. However, such adjustment possibilities are poorly incorporated in existing Swiss and European agri-environment schemes. We therefore suggest implementing regional aspects in agri-environment schemes. A first step has been undertaken in Switzerland with the introduction of the by-law for ecological quality (Bundesrat 2001). This provides extra bonus payments for hay meadows (and other ECA types) if they comply with certain ecological quality standards. These standards can be adapted to regional conditions by the local authorities.
We conclude that the Swiss agri-environment scheme targeted at hay meadow conservation preserves biodiversity. The results contribute to the assessment of the Swiss agri-environmental policy, which is presently being reviewed, and supports the justification of further payments for the preservation of ECA hay meadows (Herzog et al. 2005). We recommend that farmers should be encouraged to engage in long-term extensive management.
Obviously, not all groups of organisms can be targeted with the same efficiency by a single scheme or using a single habitat type, as was the case here for spiders. The higher spider diversity in the edge of the meadows suggests that the current management restrictions are not sufficient with respect to vegetation structure. Therefore, spider diversity may be targeted by including additional management restrictions. These could include regulating not only the time of the first cut but also the frequency of the subsequent cuts. In addition, the mowing technique might be adjusted to benefit groups of organisms that particularly depend on vegetation structure.
We still do not know, however, whether the simple extensification measures prescribed by the ECA scheme are indeed bringing back the species that have been lost during the years of intensification (Schmid 2002) or whether they simply preserve the still existing diversity. Therefore, the most important places for the protection of typical grassland species are probably species-rich meadows that have never been intensively cultivated in the first place. These old species-rich meadows might be particularly important to guarantee a large species pool for seeding the ECA hay meadows.