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European ash (Fraxinus excelsior L.) dieback caused by the fungus Hymenoscyphus fraxineus (T. Kowalski) Baral, Queloz, and Hosoya has been affecting European forests since 1992. The disease drives severe crown defoliation, branch loss, and finally tree mortality in European ash. The environmental factors affecting the disease process are still not fully recognized. We hypothesized that the level of crown defoliation in ash, as well as its impact on understory vegetation, will differ along the pH gradient in soil. We examined 27 ash stands in western Poland. We assessed the crown defoliation of 15 dominant and co-dominant trees, soil parameters (pH and soil organic matter contents; SOM), and also recorded the understory vegetation species composition. Most moderately and severely damaged trees occurred within the plots with a high SOM content (>7.5%) and neutral to slightly alkaline soil pH (>7.0) in the A horizon. We noted significantly lower crown defoliation in mesic sites with acidic soils and lower SOM contents. The results also showed the influence of ash crown defoliation on the species functional composition. Ash dieback led to the creation of gaps, and their colonization by other species frequently found in forest sites, especially forest-edge tall herbs. [ABSTRACT FROM AUTHOR]

No in‐depth studies covering litter decomposition were previously conducted on afforested postmining sites despite the importance of litter decomposition on soil formation, especially in degraded areas. We aimed to compare leaf litter decomposition rates of 14 tree species growing in mixed stands on a postmining spoil heap, and to compare their decay rates with those obtained in pure stands of tree species that are very often planted in postmining areas. The study was conducted on the Bełchatów Lignite Mine spoil heap, central Poland. We studied litter decomposition rates over 5 years using the litterbag method. Leaf litter decomposition rates (k constants; yr−1) after 5 years of the experiment were arranged from highest to lowest as follows: Prunus serotina (1.04), Alnus glutinosa (0.86), Fraxinus excelsior (0.81), Ulmus laevis (0.73), Acer pseudoplatanus (0.68), Populus tremula (0.63), Populus × canadensis (0.59), Betula pendula (0.54), Populus nigra 'Italica' (0.38), Quercus rubra (0.36), Pinus sylvestris (0.34), Robinia pseudoacacia (0.34), Fagus sylvatica (0.25), and Quercus robur (0.22). Decomposition rates increased with Mg, Ca, and summed Mg + Ca + P + K contents in freshly fallen leaves (%). All species‐specific decomposition rates were higher in mixed than in Scots pine stands. Half of them were also higher than in pure stands of other tree species. Our results indicate that tree species composition could significantly affect the physiochemical properties of upper soil horizons on reclaimed areas. Based on these findings, we recommend planting high share of not only A. pseudoplatanus, A. glutinosa, and U. laevis but also F. sylvatica and Q. robur in stands on postmining spoil heaps, because mixed stands can accelerate soil development more than pure stands. [ABSTRACT FROM AUTHOR]