[en] For the last decades we have been facing up a large and worldwide bee decline. Land use changes, such as agricultural intensification and urbanization, are largely mentioned to be responsible of this decline as they are known to have induced global biodiversity losses and a change in the nesting and floral resources for wild bees.
Our study aims to investigate the link between changes in floral resources and decline of wild bees in Belgium. In order to do so, we compiled a large historical dataset of plant species occurrences (almost 7 million data) at the country scale and we reviewed floral resources lists at the plant genus level for five declining bumblebees species (Bombus humilis, B. jonellus, B. ruderatus, B. soroeensis, B. sylvarum et B. lucorum). We splitted our resulting databases in two historical periods (1930-1970 and after 1970) corresponding to large contrasted landscape contexts in Belgium. We corrected sample bias for plants and bumblebees using Hurlbert rarefaction method. The resulting dataset allows us to observe the spatially and temporally changes in the floral resource diversity (number of genus identified as resources) and richness (% of genus identified as resources on the total number of plant genuses) by square of 4*4 km at Belgian scale and for each bumblebee species. Land use data were used to interpret these dynamics. We highlighted major changes in resource diversity for most declining bumblebees. Some squares observed a significant loss of genus richness (> 50% decrease ). These dynamics were concomitant with the expansion of cities and the agricultural landscape homogenization. Our results contribute to a better understanding of the bee decline causes. Extended to other pollinator species, our results can be used to improve the effectiveness of targeted conservation measures in floral resource deficient areas.
