Abundances of ticks at three plant communities in the Siebengebirge and Borrelia burgdorferi s.l. prevalences from 1987 to 2008. Abundances are presented as columns: Fraxino-Aceretum pseudoplatani (dark grey), the Luzulo-Fagetum milietosum (black) and the Galio-Fagetum typicum (light grey). Monthly tick abundances per 100m2 of study site from May to September of each study year were calculated; in 2001 tick densities were not determined . Borrelia prevalences for the Fraxino-Aceretum pseudoplatani, the Luzulo-Fagetum milietosum and the Galio-Fagetum typicum, are presented as circles, squares and triangles, respectively. Tick samples from 1987/89 and 2001 were examined for Borrelia infection by the immunofluorescence assay (IFA) using the same experimental protocol [15, 38]. The same ticks used for IFA in 2001 were also analyzed for Borrelia infection by nested PCR (nPCR) . Additionally, the same nPCR approach from 2001 was employed to analyze I. ricinus in 2007 and 2008. Accordingly, Borrelia prevalences from 1987/89 were compared with results from 2001, and 2001 prevalence data were compared with the data from 2007 and 2008. Borrelia infection rates were not determined in 2003 .