Influence of Local Habitat Conditions and Floral Resources on Ground-nesting bees

Sammanfattning

Pollinators provide essential ecosystem services by pollination around 80-90% of all plants, thereby supporting ecosystem functions. At present, pollinator populations are declining worldwide, rising concern about parallel declines in flowering plant diversity and broader biodiversity losses. Habitat loss is considered one of the primary drivers of pollinator decline and may have substantial consequences for ground-nesting bees, a strategy used by approximately 65-75% of all known bees. Ground-nesting bees are particularly vulnerable to habitat alteration because they depend on specific soil conditions, open nesting habitats, and availability of floral resources for successful reproduction. To address these challenges, the present study aimed to investigate how habitat characteristics and floral resources influence nesting occurrence, nesting behavior, and bee abundance among spring-active ground-nesting bees. Field surveys were conducted during spring 2026 across multiple habitats in the Gothenburg region, Sweden. Nesting sites of the ground-nesting bee species Andrena vaga, Andrena clarkella, and Colletes cunicularius were observed through field observations. Environmental variables including bare ground, vegetation, slope, aspect and solar exposure were examined in relation to nesting density. In addition, bee visitation to Salix individuals was assessed to examine how Salix sex and flower abundance influenced bee abundance. General field observations were also conducted to investigate species-specific differences in nesting behavior and nest characteristics. Relationships between habitat variables, floral resources and bee abundance were analyzed using generalized linear models, including logistic and Poisson regression models, evaluated with ANOVA. Nesting density was significant associated with steeper slopes, greater proportions open soil, and south-facing aspects. Male Salix individuals attracted a higher abundance of bees compared to female individuals. In contrast, flower abundance showed no significant relationship with total bee abundance. Field observations also indicated species-specific differences in nesting behavior and nest characteristics. Although several statistically significant relationships were identified, some findings should be interpreted cautiously due to the relatively limited number of nesting sites and observations. Together, these findings contribute to the still limited understanding of nesting ecology among spring-active ground-nesting bees and may help support future conservation and habitat restoration efforts for wild pollinators.