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（wild bees）种群出现下降趋势，亟需研发并推行有效的缓解措施。在农业景观中，提升花资源（floral resources）供给是广受认可的促进蜂类种群发展的手段，但其实际效果在不同景观与区域间存在显著差异。我们提出假说：这类差异主要由两项因素共同驱动，一是该措施对当地花资源的直接影响，二是周边景观中花资源的可获得性。 2. 为验证该假说，我们在四个欧洲国家设置了野花带（wildflower strips），统一使用专为蜂类研发的饲用植物种子混合物。我们采用前后对照-影响研究法（before–after control–impact approach），分析了野花带对熊蜂（bumblebees）、独居蜂（solitary bees）以及红色名录物种（Red List species）的影响，并探究了当地及全域景观的花资源可获得性、土地利用强度（land-use intensity）与景观复杂度（landscape complexity）对该效应的调控程度。 3. 总体而言，野花带可提升当地蜂类的丰度与物种丰富度，其中亦包含红色名录物种。野花带的实施效果随其带来的当地花丰富度差异程度提升而增强，同时还受周边景观花资源可获得性的调控，且熊蜂与独居蜂呈现出不同的响应模式。独居蜂所受的效应随景观中生长季后期替代花资源占比的提升而减弱，而熊蜂所受的效应则随全域景观生长季早期花资源可获得性的提升而增强。 4. 研究总结与实践应用。本研究表明，野花带对蜂类的效应主要取决于其提升当地花丰富度的幅度。因此，可通过两类方式强化该措施的实施效果：一是在种子混合物中最大化添加蜂类饲用植物的物种数量，二是采用可长期维持野花带花丰富度的管理方案。此外，针对熊蜂而言，本研究强调了全季持续供给食物资源的重要性。诸如种植油菜（oilseed rape）这类可提升全域景观生长季早期花资源可获得性的措施，能够为熊蜂春季种群建立与生长提供必需的食物资源，从而助力其种群发展。未来仍需开展进一步研究，以明确野花带是否能产生种群水平的效应，以及在何种条件下可实现此类效应。