List of variables measured and presented in the manuscript "Effects of climate on leaf phenolics, insect herbivory, and their relationship in pedunculate oak (Quercus robur) across its geographic range in Europe"

[Description of methods used for collection/generation of data] We sampled 168 pedunculate oaks in 2020 (25 sites) and in 2021 (34 sites) across 18 European countries (Figure 1). At each site, consisting of woods or forests of 1 ha or more, we haphazardly selected three adult pedunculate oaks. We selected the focal oaks among those with low-hanging branches that could easily be reached from the ground. In early summer – approximately 10–12 weeks after oak bud break at each site – we selected four low-hanging branches on each tree, pointing north, south, east and west directions, and haphazardly collected 30 developed leaves per branch at a random time of the day, for a total of 120 leaves per tree. Leaves were oven-dried 48 h at 45°C immediately after collection. We quantified flavonoids as rutin equivalents, hydrolysable tannins as gallic acid equivalents, and lignins as ferulic acid equivalents (Moreira et al. 2018). We obtained the quantification of these phenolic compounds by external calibration using calibration curves at 0.25, 0.5, 1, 2 and 5 μg mL-1. Phenolic compound concentrations were expressed in mg·g-1 tissue on a dry weight basis. We also quantified phenolic compound diversity at the individual plant level using two indices: phenolic compound richness, defined as the total number of phenolic compounds, and the Shannon diversity index. We assessed herbivory on a subset of 60 leaves per tree, blindly drawn from the original set of 120 leaves. These 60 leaves, along with the remaining 60 (unassessed) leaves were kept in a sealed plastic box with silica gel until they were processed for leaf phenolics and the feeding trial. We also performed a feeding experiment in 2021 and repeated 2022 with oak leaves sampled in 2020 and 2021, respectively. In total, it included 177 larvae that were reared on an artificial diet prepared from oak leaves from 55 sites (4 of the sites were sampled twice in 2020 and 2021).