The Austrian study area in Tyrol comprised seven extensively farmed grasslands and seven ecologically improved sites on formerly intensively managed land. Each improved meadow included a 2-metre-wide flowering strip along one margin. These strips were not seeded; their vegetation developed spontaneously and was mown only once, during the meadow’s second mowing event in August. The Luxembourg study area likewise included seven sites in each category. Its extensively managed grasslands were legally protected lowland hay meadows listed under European Habitats Directive habitat type 6510, while the improved sites were wildflower fallows sown in 2019 or 2020 on formerly intensively farmed land. The fallows received no management during the survey, whereas the protected meadows were cut twice yearly before 15 June or once or twice afterward.

Researchers sampled wild bees from mid-April to mid-July 2021 using white, yellow and blue pan traps. Each site contained three sets of traps, and traps were serviced during eight sampling periods, generally about every 10 days. Specimens were identified morphologically, with DNA barcoding used for selected ambiguous or taxonomically uncertain specimens. The Austrian survey recorded 1,988 wild bees from 117 species in 21 genera. The Luxembourg survey recorded 3,287 wild bees from 105 species in 17 genera. Five of the Luxembourg species—Andrena nigroolivacea, Hylaeus styriacus, Lasioglossum angusticeps, Lasioglossum pauperatum and Seladonia leucahenea—represented first national records. Honeybees were counted but excluded from the wild-bee analyses, and body size was estimated using intertegular distance as a proxy for biomass.

The Austrian comparison produced marked differences between the two management types. The seven extensively farmed grasslands contained 1,484 wild bees, compared with 504 on the seven ecologically improved sites, and their mean species richness was 35.6 species rather than 26.7. Both differences were statistically significant in Wilcoxon rank-sum tests. Estimated biomass did not differ significantly between the Austrian habitat types: the extensive grasslands contained a total of 17,028.97 mg, compared with 13,307.91 mg in the improved sites. Among the regressions testing habitat heterogeneity, only the relationship between wild-bee abundance and ecotone length involving trees, bushes, hedgerows or woods was significant in Austria. This positive relationship explained 40.6% of the variation in abundance after adjustment for multiple comparisons.

Community analyses in Austria also pointed to structural differences among sites. In analyses based on individual abundance, woody ecotones were a significant factor associated with separation between the two habitat types. The same habitat feature was significant when the analysis considered biomass-based composition, below-ground-nesting bees, polylectic species and oligolectic species, while field ecotones were significant for the above-ground-nesting subset. These are associations measured across sites, not experimental estimates of a causal effect. The surveyed Austrian grasslands also contained more above-ground-nesting, polylectic and solitary species than the improved meadows. By contrast, no significant richness difference between habitat types was detected for below-ground nesters, oligolectic species, social species or parasitic species.

Luxembourg showed the opposite arrangement. The wildflower fallows contained 2,045 wild bees, compared with 1,242 in the protected hay meadows, and their mean species richness was 39.3 species per site rather than 29.1. Both differences were statistically significant. Estimated biomass was also significantly greater in the fallows, totaling 34,304.63 mg across the seven sites, compared with 27,277.24 mg in the hay meadows. The improved sites supported more polylectic, solitary, social and below-ground-nesting species, while above-ground-nesting richness was higher by a borderline value of p = 0.050. Differences for oligolectic and parasitic species were not significant. Rank-abundance analysis showed that two highly abundant species, Lasioglossum malachurum and Andrena cineraria, occurred in both Luxembourg habitat types, although the two assemblages also included numerous habitat-specific species.

Floral resources were measured from aerial images obtained during the eight sampling periods. At an altitude of 10 metres, each image covered 385 square metres around the traps, and image pixels were classified as white, yellow or blue flowers. None of the three colour-cover measures was returned as a significant factor in the community-composition analyses. The Luxembourg fallows nevertheless contained selected plants associated with specialised bees, including Hoplitis adunca, which uses viper’s bugloss, and Dasypoda hirtipes, associated with chicory and related plants. The authors noted that unmown stems and plant debris provided nesting and overwintering opportunities for species including Hylaeus, but the study did not quantify the proportion of each Hylaeus species using hollow stems. Open soil, retained vegetation, floral quality and the timing of flowering were also not measured directly.

Landscape structure was evaluated from 20-centimetre-resolution orthophotos within an ellipse of 79,654 square metres around each site’s traps. The investigators counted habitat polygons and calculated ecotone lengths associated with trees, bushes, hedgerows and woods and with other landscape features. In Luxembourg, none of these three heterogeneity measures was significantly related to abundance, species richness or biomass. The authors suggested that unmeasured microenvironmental features, including open soil and the quantity of unmown stems, could have contributed to the observed patterns, but they also emphasized that this remains a hypothesis requiring finer-scale validation. The cross-sectional comparison cannot determine how long the effects of the fallows or reduced-mowing strips will persist or whether the same relationships apply to other landscapes.

The authors interpreted the results as support for combining the protection of stable, extensively managed grasslands with carefully designed improvements on intensively farmed land, rather than treating flower strips or protected meadows as interchangeable. They highlighted the need to account for nesting materials and nesting sites as well as pollen and nectar, and they discussed mosaic or staggered mowing, regionally tailored seed mixtures and species-specific measures as possible approaches. These are management interpretations and recommendations, not interventions tested as treatments in this study. The relatively young Luxembourg fallows had already flowered for several years, whereas the Austrian strips differed from their surrounding meadows chiefly through a less intensive mowing regime. Longer monitoring would therefore be needed to determine how floral abundance, plant richness and bee communities develop over time.

Several sampling limitations constrain the comparison. Pan traps can collect many bee species but may underrepresent large-bodied bees and can be influenced by the abundance and attractiveness of nearby flowers; no Xylocopa were captured, although 75% of Luxembourg’s known Bombus species were recorded. Spatial replication was limited to three trap sets per site, and the mid-April to mid-July period captured mainly spring- and early-summer-flying species while neglecting most late- and autumn-flying bees. Rarefaction analysis indicated similar sampling effort among habitat types but no saturation in the species-richness curves. The authors proposed longer-term monitoring, additional sampling methods such as Malaise or vane traps, direct observations, and more detailed measurements of floral resources, microhabitats, pesticides and forever chemicals. Within these limits, the study shows that bee conservation outcomes differed sharply between two Central European agricultural landscapes, underscoring the need to evaluate restoration measures in their local habitat and management context.

Subject of Research: Comparative assessment of habitat heterogeneity and ecological improvement in Central European agricultural grasslands

Article Title: Wild Bee Conservation: Habitat Heterogeneity and Ecological Improvement in Agricultural Land With Open Grassland

Article References: Lanner, J., Bühler, P., Hellers, L., Kopf, T., Weigand, A., Schlick‐Steiner, B. C., & Steiner, F. M. (2026). Wild Bee Conservation: Habitat Heterogeneity and Ecological Improvement in Agricultural Land With Open Grassland. Ecology and Evolution, 16(10), Article e74514. https://doi.org/10.1002/ece3.74514

Image Credits: AI Generated

DOI: 10.1002/ece3.74514

Keywords: wild bees, habitat heterogeneity, wildflower fallows, grassland conservation, ecotones, agricultural land, Austria, Luxembourg, pollinator ecology, flower strips, Wild, Conservation