Ticks in the landscape: Fragmentation impacts density of Europe’s principal tick-borne disease vector, Ixodes ricinus, across Germany

Tick-borne diseases (TBDs) constitute a considerable challenge for human and animal health. Understanding the driving forces of TBD risk is key to developing effective prevention strategies, particularly in light of human-nature interfaces or increasing anthropogenic land transformation. Landscape features may influence local tick abundance by modulating biotic and abiotic conditions and tick host space use. The present country-wide study analysed the relationship of landscape composition with the local density of the most important TBD vector in Europe, Ixodes ricinus, determined at 83 sites across Germany during 2018-2020. Land cover data were analysed within a 500-m, 1000-m, and 2500-m buffer around the 83 tick collection sites. Additionally, satellite images were used for a more accurate assessment of habitat fragmentation, edge habitat, and the presence of paved streets in the 500-m buffer. Generalised linear mixed models were constructed, including meteorological variables to account for regional differences in climate. A higher fragmentation index and an increasing proportion of coniferous forest within the 500-m buffer were associated with significantly lower questing I. ricinus nymph density. In the subset of sites dominated by total forest or shrub cover within the 500-m buffer, the cumulative length of paved streets also had a significant negative impact. At the same time, increasing broad-leaved forest within the 1000-m buffer and total forest cover within the 2500-m buffer were additional significant predictors of lower tick density. These contrasting patterns detected at different spatial scales may indicate that I. ricinus thrives most in forest patches of intermediate size that form a heterogeneous landscape mosaic with agricultural or urban areas.