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Fig. 1. Vegetation zones and the locations of the 22 forest areas. HB = hemiboreal, SB = southern boreal, MB = middle boreal, and NB = northern boreal zone.

Table 1. Dead-wood (CWD) tree species, total numbers of CWD units, the mean numbers and standard deviations of each tree species CWD in study areas, and polypore numbers found on them.
Tree species Total no. of CWD units Mean (SD) no. of CWD units/ha Polypore occurrences Polypore species Unique species Red-listed species
Acer platanoides 4 0.08 (0.4) 2 2 0 0
Alnus glutinosa 219 3.7 (16.3) 152 20 1 1
Alnus incana 944 25.7 (61.7) 264 30 1 1
Betula spp. 1054 19.4 (23.5) 932 41 8 2
Corylus avellana 1 0.03 (0.2) 1 1 0 0
Juniper communis 3 0.07 (0.3) 0 0 0 0
Picea abies 1399 24.2 (25.8) 993 44 16 6
Pinus sylvestris 274 5.1 (10.2) 103 24 4 1
Populus tremula 242 4.5 (10.0) 163 20 6 2
Prunus padus 54 0.9 (2.7) 28 10 0 0
Salix caprea 298 5.8 (13.1) 147 24 2 1
Salix spp. 12 0.7 (4.9) 4 2 0 0
Sorbus aucuparia 131 2.4 (6.8) 31 15 1 1
Tilia cordata 11 0.2 (0.8) 3 2 0 0
Unidentified 56 1.2 (5.0) 2 3 0 0
Unidentified conifer 43 1.1 (4.1) 3 3 0 0
Unidentified deciduous 56 1.1 (2.8) 4 4 0 0
Total 4797 96.2 (77.2) 2832 101 39 12
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Fig. 2. Proportion of coniferous and deciduous coarse woody debris (CWD) among size classes (a), substrate types (b), and decay stages (c). Substrate types: 1, standing dead trees and >1.3 m high snags; 2: downed intact and broken logs; 3: branches and roots; 5: natural stumps, <1.3 m high; 6: logging residual and man-made stumps, logs, and bolts. CWD items not identified as either coniferous or deciduous are not displayed.

Table 2. Spearman rank-order correlation coefficients between stand-scale variables, percentage of coarse woody debris (CWD) items inhabited by polypores, polypore species richness, number of occurrences, red-listed species richness and polypore diversity.
N coordinate Area CWD total CWD/ha CWD30/ha CWD diversity Inhabited Species richness Occurrences Red-listed species
Area –0.12
CWD total 0.27* 0.23
CWD/ha 0.33** –0.47*** 0.72***
CWD30/ha –0.34** –0.03 0.16 0.14
CWD
diversity 		–0.16 0.26* 0.53*** 0.31** 0.32**
Inhabited –0.54*** 0.01 –0.42*** –0.39*** 0.27* –0.18
Species
richness 		–0.42*** 0.34** 0.39*** 0.13 0.38** 0.64*** 0.35**
Occurrences –0.19 0.35** 0.55*** 0.27* 0.30* 0.46*** 0.40*** 0.78***
Red-listed species –0.07 0.18 0.07 –0.10 0.28* 0.09 0.23* 0.26* 0.19
Polypore diversity –0.43*** 0.20 0.25* 0.07 0.39*** 0.69*** 0.12 0.85*** 0.44*** 0.17
CWD total, total number of CWD items; CWD/ha, coarse woody debris items per hectare; CWD30/ha, number of CWD items with a diameter of >30 cm per hectare; Inhabited, percentage of CWD items inhabited; Occurrences, total number of polypore observations; Red-listed species, number of R-L species.
* = p < 0.05; ** = p < 0.01; *** = p < 0.001.
Table 3. Summary of linear regression models for total polypore species richness. Variables used in the models were the diversity of coarse woody debris (CWD) items, northern coordinate, and number of large (diameter > 30 cm) CWD items per hectare.
Variable Coefficient p F1,69 R2
Diversity of CWD 6.939 <0.001 57.73 0.455
N-coordinate –1.039×10–5 <0.001 13.76 0.166
Large CWD per hectare 0.187 0.006 8.05 0.105
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Fig. 3. Species accumulation curves for different size classes of coarse woody debris (CWD) items. The lines are mean (expected) number of species for a given number of CWD items sampled.

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Fig. 4. Mean number of occurrences of polypores in different coarse woody debris (CWD) size classes and host tree species. The vertical lines indicate standard deviation. Bsp: Betula spp.;, Ptre: Populus tremula; Blt: Other deciduous trees, Pabi: Picea abies; Psyl: Pinus sylvestris.

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Fig. 5. Two-dimensional solution of non-metric multidimensional scaling (NMDS) ordination based on Bray-Curtis dissimilarities between polypore assemblages on different tree species in each forest stand. Stress value = 0.12. The polypore species scores of the NMDS solution are given in Supplementary file S3.

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Fig. 6. A two-dimensional NMDS solution locating polypore species, and fitted environmental factors. Only environmental factors with p-value < 0.05 are displayed: Pabi, Picea abies (r = 0.39); Blt, other deciduous trees (r = 0.35); y_co, northern coordinate (r = 0.34); area, size of the surveyed area (r = 0.16); Bsp, Betula spp. (r = 0.13); nobles, so-called noble tree species (Tilia cordata, Acer platanoides and Corylus avellana) (r = 0.13). The tree species vectors are given as the number of coarse woody debris (CWD) of each tree species per hectare. Red-listed species are shown in bold. The polypore species scores of the NMDS solution are given in Supplementary file S4. View larger in new window/tab