The intensity (stronger = darker shading) of nine density/biomass variables (A; used for SOM training) and eight explanatory variables (B; not used for SOM training) in particular SOM regions.

Values of the A variables come from the virtual sampling terms (one per output neuron), whereas values of the B variables are the means of the real sampling terms assigned to a given output neuron (see S1 Fig). The intensity of the grey colour is scaled independently for each variable (the range of variability in the data set is presented on the right side of each plane). Zarzęcin (ZA), Bronisławów (BR) and Tresta (TR) are the sampling stations. See Figs 7 and 8 for statistical verification of the differences between the SOM sub-clusters.