From May to November 2003, at five selected sites of the 'Siebengebirge', a nature reserve near Bonn, Germany, data on microclimate, pedology, plant sociology and tick abundance were collected weekly and correlated. A total of 2832 host-seeking Ixodes ricinus (2660 nymphs and 172 adults) were collected, with maximal abundance in June and a minor second increase in abundance in August. The spatial and temporal variation in tick abundance was closely related to the air temperature, relative humidity, soil water content and specific vegetation type. Increases in tick abundances in individual habitats were most likely caused by climate change and/or anthropogenic interventions such as increased numbers of wild boar, a host of I. ricinus. When combined with data from previous investigations a correlation of plant communities with six semi-qualitative tick abundance categories (ranging from 'no ticks' to 'very high tick abundance') was revealed, and GIS analysis indicated that 56.5% of the 'Siebengebirge' is made up of plant communities belonging to the three highest tick abundance categories. Therefore, the risk of visitors in the 'Siebengebirge' of being exposed to tick bites and being infected by Borrelia burgdorferi sensu lato had increased.