A century of local changes in bumblebee communities and landscape composition in Belgium

Bumblebees (Bombus spp.) are declining in most parts of Western Europe. Many studies have highlighted the role of agricultural intensification and urbanisation in this decline, and some have also shown the influence of landscape composition on bumblebee populations. However, very few studies have explored bumblebee communities prior to the onset of these major land use changes, and those studies that do are mostly based on low-resolution spatial data. Here, we perform a comparative analysis based on detailed landscape composition and bumblebee occurrence records between the early twentieth century (1910-1930) and the contemporary period (2013-2015) in four localities representative of Belgium. We show that bumblebee assemblages changed drastically over this period, and that the decline in richness was strongest in areas with the greatest increase in urbanization and agricultural intensification. The one locality still retaining a high proportion of grasslands, orchards and woodlands with the smallest overall change in landscape composition still hosts a rich bumblebee fauna, very similar than in the past. We provide recommendations for land use management based on these findings. We also warn about the importance of other factors such as land use intensity, climatic conditions and altitude, which should be included in any future study addressing changes in bumblebee populations related to land use changes.