Fig. 1.

Pollen collection in the Netherlands a) locations of pollen monitoring sites, the West (Leiden) and South-east of the Netherlands (Helmond) b) Hirst-type Burkard pollen sampler c) sample selection of Melinex tapes and microscopic slides with mounted tapes d,g) 20-year average pollen concentrations of Alnus, Cupressaceae and Urticaceae at both pollen monitoring stations e,h) 2019 pollen concentrations of the three target taxa and f,i) 2020 pollen concentrations. Sampling dates are shown with red diamonds on the x-axis. Note scale change for figure e and h. NL = the Netherlands, yr = year. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)