Effect of magnesite dust pollution on biodiversity and species composition of oak-hornbeam woodlands in the Western Carpathians

We aimed to identify how the alkaline dust fallout from magnesite factories (Slovenske rudohorie Mts, Western Carpathians) affects biodiversity and species composition of oak-hornbeam forests, and to compare sensitivity of local biodiversity represented by vascular plants (including flowering plants and ferns) and cryptogams (cyanobacteria, macromycetes, slime molds, lichens, bryophytes). Altogether 24 plots were sampled along four degradation stages during the vegetation seasons 2011-2016: A - poorly developed vegetation on the magnesite crust, B - dense grassland vegetation almost without a tree-layer, C - degraded woodland with opened canopy, and D - visually unaffected original closed-canopy woodland. For each plot we sampled phytocoenological releves including vascular plants and terrestrial cryptogams (cyanobacteria, lichens and bryophytes), and presence records for epiphytic lichens, epiphytic bryophytes, sporocarps of macromycetes (terrestrial, saprotrophic, parasitic and ectomycorrizal) and sporocarps of slime molds. We also analyzed concentrations of C, Ca, Mg, S, N, P, K in the soil, light conditions, bark pH and the distance from two emission sources (ES). Increased alkaline dust, corresponding to a smaller distance from the emission source correlated with higher concentrations of Mg, Ca, Fe, S, C/N in soil samples. Regressive succession converted oak-hornbeam woodland to degraded woodland with opened canopy, further to ruderal grasslands, then to halophilous procoenoses of Agrostis stolonifera and Puccinellia distans on degraded soils with eroded magnesite crust and biocrusts (formed by cyanobacteria Microcoleus steenstrupii, Nostoc microscopicum and Schizothrix arenaria; bryophytes Desmatodon cernuus, Didymodon tophaceus; pioneer terrestrial lichen Thelidium zwackhii) and finally into habitat with no vegetation. This is the first report on early successional stages with halophilous procoenoses in the Western Carpathians. We also recorded significant differences in species richness and the species pools in all organism groups along the gradient. Overall species diversity decreased. The degradation stages are characterized by low representation of symbiotic macromycetes and by a high proportion of saprotrophic macromycetes. The highest species richness of vascular plants was recorded in degradation stages B and C, the highest herb-layer cover in stage B. The highest species richness of terrestrial bryophytes is also found in dense grassland vegetation in stage B. Occurrence of nitrophilous epiphytic lichens differentiates unaffected oak-hornbeam woodlands from the plots close to the emission source.