Sand nesting bees in the age of urbanization: availability and quality of sandy habitat for wild bee biodiversity

Little is known about urban wild bee communities and their requirements for nesting sites, especially for sand-nesting bee communities. Wild bee biodiversity is in decline. In Sweden alone a third of wild bee species are threatened and red listed (Borgström et al. 2018). Rapid urban development and expansion is one of the driving causes of this decline. A deeper fundamental knowledge of wild bee nesting site availability and quality in an urban setting can improve efforts to preserve these sites and maintain wild bee communities and biodiversity.

To assess habitat quality, variables such as ground temperature, slope, solar exposure, vegetation cover and site connectivity between suitable nesting sites was evaluated for their importance for soil nesting bee biodiversity. The study was carried out in southern parts of central Uppsala, Sweden and addresses over 75 years of urban development and its impact on sandy habitat from 1942 until present. Therefore, the age of sand habitat was also assessed as a variable for habitat quality. Additionally, this study examines the potential benefits or consequences of sand translocation as a management plan by the municipality in attempt to preserve wild bee communities during urban expansion.

The preliminary results shows that the quality of the sand is an important factor for soil nesting wild bee biodiversity: finer sand habitats seem to host a larger biodiversity of soil nesting bees than coarser sand habitats at the studied sites. Furthermore, small sized habitats seemed to provide a higher diversity of wild bees than large habitats in the study area. However, it does not mean that in general smaller habitats are better for the biodiversity, as this result can be coincidental considering the majority of small habitats in the study area were artificially created as a management practice to increase nesting resource for insects.

Creation of small sized sand patches in an urban environment where natural areas of such habitats are being replaced by the process of urbanization can provide an adequate habitat for diverse soil nesting wild bees. This study provides practical information to be considered for establishing such habitats, such as importance of the quality of sand; finer sand can provide a more attractive nesting source for many wild bee species than coarser sand.