Agri‐environment schemes enhance pollinator richness and abundance but bumblebee reproduction depends on field size

Abstract

Pollinators have experienced a dramatic decrease world‐wide due to agricultural intensification. In many countries, agri‐environment schemes (AES) have been introduced to counteract this current trend. However, until now, the relative importance of each AES for biodiversity and ecosystem services is still little understood and might change depending on landscape context. Complex landscape‐experiments are required to fill this knowledge gap, enabling the implementation of sustainable intensification of food production. In our study, we compared the effectiveness of the two most popular AES in Germany, organic farming and flower strips, in supporting pollinators and flower resources. We selected nine landscapes along a gradient of increasing field size, (configurational heterogeneity), each with a triplet of winter wheat fields: one organic, one conventional with flower strip and one conventional without flower strip as a control. We surveyed insect‐pollinated plants and pollinators (bumblebees, solitary bees and hoverflies). Additionally, we placed bumblebee colonies in the field edges to monitor their growth (colony weight gain) and reproduction (queen production). Flower strips stood out with the highest abundance and richness of pollinators. In contrast, bumblebee colony growth and plant richness benefited equally from organic and flower strip schemes. At the landscape scale, smaller fields had a positive effect on plant richness and bumblebee reproduction in flower strips. By contrast, bumblebee colonies in organic agriculture benefited most from large fields, as large organic fields provided much more flower resources than the narrow flower strips. Synthesis and applications. Our results showed that both local and landscape management shaped pollinator communities and their reproduction. Overall, organic farming and flower strips appeared to be effective tools to mitigate flower shortage in conventional cereal fields, with organic farming supporting the highest flowering plant cover per field. Flower strips enhanced local pollinator richness most, but increased bumblebee reproduction only when the surrounding landscapes had small fields with long field borders. Therefore, our results reveal that European Union policies need to take into account that the effectiveness of agri‐environment schemes depends on the structure of the surrounding landscape.

Scale-depend effectiveness of on-field vs. off-field agri-environmental measures for biodiversity

“…1b). When FS occupy 15% of a conventional field, which was the situation in our study (Geppert et al 2020), the effectiveness of conventional management with FS was still 43% higher than the effectiveness of organic management (compared to conventional fields without FS). Hence, the difference at field level is much less expressed than in the transect scenario.…”

“…In this scenario, comparisons consider the transect level, i.e. sampling of pollinator data at the transect level of organic vs. conventional vs. FS (adjacent to conventional fields) (Geppert et al 2020), exhibiting an eight times higher effectiveness of FS than organic management (Fig. 1a).…”

“…A plethora of studies addresses the ecological effectiveness of different agri-environment schemes with nearly all of them focusing exclusively on the transect level (Batáry et al 2015), whereas upscaling to higher spatial scale (field or farm level) is rare (Batáryet al 2017). Although small-scale off-field measure can have a very positive biodiversity outcome at that scale, such as in case of flower strips, upscaling to field and farm level can reveal that the biodiversity benefit of FS is on par or even lower than that of on-field measures such as organic farming (Geppert et al 2020). Focusing studies on the transect scale can give misleading results, as FS make up typically only ca.…”

Beyond the Decline of Wild Bees: Optimizing Conservation Measures and Bringing Together the Actors

“…Introduced in the 1980s, the impact of AES was rarely tested until recently [131]. Among them, Geppert et al [132] tested the impact of organic farming and flower strips. Overall, both measures were positively correlated with pollinators' richness and abundance as well as bumblebee colony growth, but the effectiveness of these measures depended also strongly on the surrounding landscape [132].…”

“…Among them, Geppert et al [132] tested the impact of organic farming and flower strips. Overall, both measures were positively correlated with pollinators' richness and abundance as well as bumblebee colony growth, but the effectiveness of these measures depended also strongly on the surrounding landscape [132]. Wood et al [133] also evaluated a specific agri-environment scheme (i.e., Higher Level Stewardship farms-HLS) to test if sown flowers benefited to wild solitary bees in England.…”