Fig. 1

Annual variation in log₁₀-transformed cumulative nymphal density (CND) and beech tree mast score 2 years prior. The log₁₀-transformed CND (dots and solid lines) and the beech tree mast score 2 years prior (grey bars) are shown over time for each of the three elevation sites (low, medium, high) on Chaumont Mountain. The log₁₀-transformed CND increased significantly over the 15-year study period (2004–2018). Years of high seed production by beech trees (beech masting index) are strongly positively correlated with high log₁₀-transformed CND two years later. The CND is an estimate of the annual abundance of I. ricinus nymphs per 100 m² and is calculated by integrating the area under the curve of the 12 monthly estimates of the number of questing nymphs collected by dragging an area of 100 m². Beech tree mast scores range from 1 to 5 (1, very poor mast; 2, poor mast; 3, moderate mast; 4, good mast; and 5, full mast)