Abstract
Ecological Focus Areas (EFAs) to benefit biodiversity became mandatory in intensively farmed landscapes after the reform of the European Common Agricultural Policy (CAP) in 2013. The implementation of EFAs as uncropped field margins has been criticized as ineffective but created a window of opportunity to test if augmenting them with annual flower strips can benefit biodiversity. In this study, we investigated if annual flower strips on EFAs benefited functional biodiversity in intensively farmed landscapes. To this end we established eleven annual flower strips with a seed mixture targeted for both natural enemies and pollinators, on areas were farmers had planned for EFAs. We determined effects on aphids and their natural enemies in cereal fields close to six of the flower strips, and for solitary bees and wasp close to and in the surroundings of all eleven flower strips. We found that annual flower strips benefited the abundance of hoverfly larvae and possibly also that of solitary bees. However, there were neither any significant effects on natural enemies (other than hoverfly larvae), nor any difference in natural pest control as shown by lack of differences in aphid numbers and parazitation rates. Abundances of solitary bees and wasps in the surrounding landscapes were unaffected, although there was a tendency for more solitary bee cells closer to the strips. We suggest that the critical issue leading to the mostly negative results is the lack of permanent structures to sustain populations of arthropods that in turn can benefit from annual flower strips. Hence, future agri-environmental policies need to carefully consider if and how annual agri-environmental measures should be implemented in intensively managed agricultural landscapes, e.g., by combining them with more permanent structures.
Highlights
Flower strips are often proposed as a tool to mitigate biodiversity loss in agricultural landscapes (Haaland et al, 2011), especially loss of functional biodiversity such as pollinators (Scheper et al, 2013) and natural enemies of pests (Holland et al, 2016)
Given the lack of scientific foundation on the use of annual flower strips on Ecological Focus Areas (EFAs) to benefit functional biodiversity, we in this study aimed to evaluate if they benefited natural enemies and pollinators in the surrounding landscape
Given that EFAs are mandatory mostly in intensively farmed landscapes, and that benefit of functional biodiversity for cash crops is most relevant in these landscapes (Nilsson et al, 2019), we evaluated the effect using experimental implementation of annual flower strips in existing EFAs in replicated simple landscapes
Summary
Flower strips are often proposed as a tool to mitigate biodiversity loss in agricultural landscapes (Haaland et al, 2011), especially loss of functional biodiversity such as pollinators (Scheper et al, 2013) and natural enemies of pests (Holland et al, 2016). Supporting biodiversity-related ecosystem services has the potential to increase agricultural production while minimizing negative environmental impacts (Bommarco et al, 2013). The consequences of agri-environmental measures such as flower strips, on functional diversity may be context dependent, and related to the agricultural intensity in the surrounding landscape (see e.g., Tscharntke et al, 2005, 2016; Bianchi et al, 2006; Scheper et al, 2013; Grab et al, 2018). The re-occurring critique toward the European Union’s (EU), Common Agricultural Policy (CAP), that measures need to be targeted (e.g., Smith et al, 2010; Batáry et al, 2015; Pe’er et al, 2019) and based on a landscape perspective (see e.g., Tscharntke et al, 2005; Batary et al, 2011; Kleijn et al, 2011), applies to flower strips
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