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Our study focuses on the ground vegetation dynamics and its dependence on microsite conditions in declined climax mountain Norway spruce forests during the recovery period (1995–2006) following upon the considerable decrease of SO2 pollution. We showed that ground vegetation development shifted from prevailing mosses and vegetation-free sites covered with spruce litter to dominance by Avenella flexuosa during the earlier period of massive decline of the observed ecosystems. The expansion of Vaccinium myrtillus seems to occur mainly under the gradually defoliating tree crowns whereas larger canopy gaps and quickly deforested areas are more successfully colonized by grasses, especially Calamagrostis villosa. The gradual spruce stand decline, as well as the corresponding ground vegetation dynamics, proceeded until the end of the twentieth century. Afterwards, the ground vegetation responded to the interruption of trees dying and stopped its expansion on spruce litter microsites. Retreat of both dominant grasses accompanied by the remarkable increase in cover of mosses occurred. [ABSTRACT FROM AUTHOR]

There is a concern that soil acidification by acidic deposition, along with the resulting depletion of the labile pool of nutrient cations (e.g. Ca, Mg) and enhanced leaching of Al from soil may contribute to forest dieback. The molar ratios of Ca/Al or (Ca+Mg+K)/Al in the soil solution have been widely used as a criterion for risk of tree damage due to acidification. Intensity and quality of the crown and branch structure transformation due to formation of secondary shoots in successive series is a very sensitive indicator of long-term tree damage, and the subsequent regenerative processes. Soil water chemistry and crown structure transformation of Norway spruce were observed at 16 forest plots within the Czech Republic with the following results: parameters, expressing degradation processes in the crown (defoliation of primary structure), regeneration processes (percentage of secondary shoots) or synthetic stages of crown structure transformation showed high correlation with soil water (Ca+Mg+K)/Al ratio in organic horizons. No relationships were found for mineral horizons. The correlations between soil water and crown status parameters were considerably stronger when using the (Ca+Mg+K)/Al ratio rather than the Ca/Al ratio. [ABSTRACT FROM AUTHOR]