What evidence exists on wild-bee trends in Germany? Research protocol for a systematic map

Wild bees have inspired scientists and citizens by their fascinating diversity, beautiful appearance and the benefit humans obtain via plant pollination (Klein et al. 2018). They receive a widespread public attention and were used in recent popular petitions from the civil society in Germany campaigning for a reversal of insect decline (Süddeutsche Zeitung 2019). Their interaction with flowering plants has been researched intensively over the past decades (Jordano et al. 2003; Garibaldi et al. 2013; Potts et al. 2016; Benadi and Pauw 2018). The decline of wild-bee and in more general pollinator diversity has been documented worldwide and is assumed to hold true for Germany (Biesmeijer et al. 2006; Potts et al. 2010; Schwenninger and Scheuchl 2016). Nevertheless, information on wild-bee trends from the country that has launched the current political debate on declining insects (Hallmann et al. 2017; Seibold et al. 2019) are scarce and knowledge about German wild-bee communities is scattered. In Germany there are a range of entomological, in general locally organised associations, and 16 regional governments responsible for nature protection measures and potentially storing wild-bee records. Collecting and synthesising this knowledge is a tedious task, but promises to substantially increase the knowledge about wild-bee population trends in Germany. The scope of the study is to identify trends in wild-bee populations in Germany. Therefore, we aim to identify data available on temporal trends of wild-bee communities, predominantly in agricultural areas, but also in urban areas and forests. The systematic map results will be used by practitioners specifically targeting conservation actions for wild bees and allow them to identify suitable habitat types in the past, present and future most particularly in Germany, but even across Europe.