Fig. 1: Primary forest sites in relation to forest cover in Europe.

Primary forest sites included (i) research sites and (ii) sites reported in the literature that were selected by observation of ecological characteristics, and (iii) forest inventory sites described as primary forest or as natural forest >100 years old and under some protection status. Forest cover was defined by area of CORINE forest types94 and forest canopy cover ≥30% (S1.7) (See Methods: Identification of primary forest sites).