Variable Explanation CanopyOpenness "Measured as the proportion of visible sky in a photo taken towards the sky from the surface of the downed trunk using a 180° lens; %" Category Type of the forest site: either urban or semi-natural Commune Name ofthe commune where site was located DailyMaximum4hTemperatureChange "Based on temperature measurements between 1 May and 29 September 2019; see the README file; °C" DecayClass Following Renvall's (1995) classification Diameter cm DistanceFromEdge meters DNA_sampling_date Time when the DNA sample was collected (YYYY-MM-DD) Elevation meters (value from GPS) EpiphyteCover "Measured as the cover of bryophyte mats on the upper surface of the trunk; %" GroundVegetationCover "Measured as the proportion of vegetated ground surface in a 10 × 10 m square around the tree trunk; %" Height "Distance to ground contact; cm" InvSimpsonDiv Diversity metric of the fungal community (inverse Simpson concentration) calculated based on relative species and OTU abundances Latitude degrees Longitude degrees RedListedSpecies "Number of red-listed fungal species detected in the trunk as DNA; see the README file for more detailed information about which species were considered" Sample Sample code (TrunkNo_SegmentNo) SegmentNo Numerical code for trunk segment (1-4) SequencingDepth Number of raw (before quality filtering) sequence reads per sample from Illumina sequencing SiteName Name of the forest site SiteNo Numerical code for forest site TempMax "Maximum temperature inside the tree tunk between 1 May and 29 September 2019; °C" TempMean "Mean temperature inside the tree tunk between 1 May and 29 September 2020; °C" TrunkFallType "3 - uprooted tree; 4B - broken tree; 10B - felled tree" TrunkNo Numerical code for tree trunk WoodMoisture "Measured based of electric resistance; %"