This year has been named by the UN as the International Year of Biodiversity, after governments decided in 2001 to halt the loss of biodiversity by the end of the decade - a goal which is a long way from being met. As a mark of support (and a critique of the lack of progress), shepherds from different countries assembled the flock for the Berlin-to-Brussels drive.

Flocks are regularly moved to seasonal pastures, extending the range of grazing land and allowing time for renewed growth. That process, called transhumance, has the unintended benefit of allowing the sheep to act as a seed vector, carrying plant seeds over long distances and allowing them to spread to areas where they do not compete with the parent plants. But transhumance is becoming less common, particularly in more developed countries.

The Belgian leg of the drive is under the control of Johan Schouteden, who keeps sheep and cows on Sonnisheide farm in Helchteren, Limburg province. "We'll be trying to travel with the sheep through the peaceful, rural areas of Flanders - through the natural sand paths that are still left in our landscape," Schouteden said. A blog following the day-by-day progress of the trek is at www.herderstocht.be/blog.