Sampling network
The present study is part of an ongoing citizen science project that involved so far a total of 93 participants, including 41 scientists and 52 partner schools from 17 European countries (Castagneyrol et al., 2019; Valdés-Correcher et al., 2021) covering most of the native geographical range of the pedunculate oak (Figure 1A ). We geolocalized and surveyed a total of 298 mature oak trees in forest and urban areas during 2018 (n = 132), 2019 (n = 56), and 2020 (n = 113) (Figure 1 ).