How quickly do flower strips in cities help the local bees?

Many cities are introducing green areas to protect their fauna. Amongst such measures are flower strips, which provide support to flower-visiting insects, insect- and seed-eating birds. According to the first quantitative assessment of the speed and distance over which urban flower strips attract wild bees, conducted at the University of Munich and published in the open-access Journal of Hymenoptera Research, one-year-old flower strips attract 1/3 of the 232 species recorded from Munich since 1997.