Data from: Local and landscape-level floral resources explain effects of wildflower strips on wild bees across four European countries

1. Growing evidence for declines in wild bees calls for the development
and implementation of effective mitigation measures. Enhancing floral
resources is a widely accepted measure for promoting bees in agricultural
landscapes, but effectiveness varies considerably between landscapes and
regions. We hypothesize that this variation is mainly driven by a
combination of the direct effects of measures on local floral resources
and the availability of floral resources in the surrounding landscape. 2.
To test this, we established wildflower strips in four European countries,
using the same seed mixture of forage plants specifically targeted at
bees. We used a before–after control–impact approach to analyse the
impacts of wildflower strips on bumblebees, solitary bees and Red List
species and examined to what extent effects were affected by local and
landscape-wide floral resource availability, land-use intensity and
landscape complexity. 3. Wildflower strips generally enhanced local bee
abundance and richness, including Red-listed species. Effectiveness of the
wildflower strips increased with the local contrast in flower richness
created by the strips and furthermore depended on the availability of
floral resources in the surrounding landscape, with different patterns for
solitary bees and bumblebees. Effects on solitary bees appeared to
decrease with increasing amount of late-season alternative floral
resources in the landscape, whereas effects on bumblebees increased with
increasing early-season landscape-wide floral resource availability. 4.
Synthesis and applications. Our study shows that the effects of wildflower
strips on bees are largely driven by the extent to which local flower
richness is increased. The effectiveness of this measure could therefore
be enhanced by maximizing the number of bee forage species in seed
mixtures, and by management regimes that effectively maintain flower
richness in the strips through the years. In addition, for bumblebees
specifically, our study highlights the importance of a continuous supply
of food resources throughout the season. Measures that enhance
early-season landscape-wide floral resource availability, such as the
cultivation of oilseed rape, can benefit bumblebees by providing the
essential resources for colony establishment and growth in spring. Further
research is required to determine whether, and under what conditions,
wildflower strips result in actual population-level effects.

1. 越来越多的证据表明野生蜂类种群数量下降，亟需开发并实施有效的缓解措施。在农业景观中，提升花类资源是公认的促进蜂类生存的手段，但其实施效果在不同景观与区域间差异显著。我们提出假设：这种差异主要由两方面共同驱动——一是该措施对当地花类资源的直接影响，二是周边景观中花类资源的可获得性。2. 为验证这一假设，我们在四个欧洲国家布设了野生花带，采用专门针对蜂类的同种饲用植物种子混合物。我们采用前后对照-影响（before–after control–impact, BACI）实验设计，分析野生花带对熊蜂、独居蜂以及红色名录物种的影响，并探究当地和景观尺度的花类资源可获得性、土地利用强度以及景观复杂度对实验效果的影响程度。3. 总体而言，野生花带可提升当地蜂类的种群丰度与物种丰富度，涵盖红色名录物种。野生花带的有效性随其营造的当地花类丰富度梯度提升而增强，同时还受周边景观花类资源可获得性的调控，且独居蜂与熊蜂呈现出截然不同的响应模式：景观中季晚阶段替代花类资源占比越高，对独居蜂的促进效果越弱；而景观季早阶段花类资源可获得性越高，对熊蜂的促进效果越强。4. 总结与应用：本研究表明，野生花带对蜂类的影响很大程度上取决于其提升当地花类丰富度的幅度。因此，可通过在种子混合物中最大化添加蜂类饲用植物物种，以及采用能长期维持花带内花类丰富度的管理方案，来提升该措施的有效性。此外，针对熊蜂而言，本研究强调了全年持续供给食物资源的重要性：提升景观尺度季初花类资源可获得性的措施（例如种植油料油菜），可通过为熊蜂春季种群建立和生长提供必需资源，从而惠及熊蜂种群。未来仍需进一步研究，以明确野生花带是否能产生实际的种群层面效应，以及其生效的具体条件。