How do soil factors determine vegetation structure and species richness in post-smelting dumps?

•The effect of slag substrate on pioneer vegetation structure was assessed.•Three different responses of species to substrate contamination were recognized.•Lichens and vascular plants respond differently to soil contamination.•Certain cryptogams are indifferent to contamination and well adapted to slag substrate.•Restoration at slag dumps should be aimed at the maintenance of cryptogamic vegetation.

This study aims to determine the effects of extreme heavy metal contamination and other soil factors on the structure and species richness of pioneer communities on artificial slag-soil substrates. Lichens, bryophytes, and vascular plants were examined in study plots and chemical properties of corresponding substrate samples were analyzed. Species responses to soil factors were identified by detrended correspondence analysis with interpretation of ordination axes and identification of significant soil parameters using linear mixed-effects models. The interrelationships between species richness and soil factors were evaluated by generalized linear mixed-effects model with Poisson error distribution. Three different responses to substrate contamination were recognized: species most tolerant and favored by strong contamination, less resistant species appearing only on less contaminated dumps and cryptogams indifferent to heavy metal contamination and abundant on all dumps. The species richness of lichens and vascular plants respond differently in relation to heavy metal contamination. Our results indicate that certain cryptogamic species are indifferent to enormous contamination and well adapted to slag substrate. In contrast, highly elevated levels of heavy metals negatively affect vascular plant species richness. Assemblages of pioneer cryptogams are an important element in the natural regeneration of post-smelting wastes and should be taken into account when reclamation activities are planned.