Fig. 2

a Thirty-four Level II plots belonging to the ICP Forests network have been used so far for mycorrhizal assessments. Dark grey circles are Scots pine plots sampled by Cox et al. (2010b), and light grey circles are oak plots sampled by Suz et al. (2014). b A schematic map of a typical Level II plot shows the presence of numbered trees that facilitates randomisation of tree to tree transects for mycorrhizal root sampling within plots, as well as allowing the spatial location of samples to be recorded should within-site spatial analyses or re-sampling be required