Are the dynamics of natural subalpine spruce ( Picea abies (L.) Karst.) forests of central Europe governed by stand-replacing disturbances caused mostly by winds or by moderate disturbances resulting from bark beetle outbreaks? We analyzed tree-ring series from subalpine spruce forests in two mountain ranges of the Western Carpathians to determine the frequency and severity of disturbances and their effects on tree recruitment. The boundary-line method was employed to identify significant growth releases, interpreted as results of disturbances. In both study areas, major releases were not numerous but were regularly distributed over time. We found no evidence for stand-replacing disturbances. This result contrasts sharply with earlier findings from the Western Carpathians. The age structure of the forests studied indicates that the amount of tree recruitment was greater 150–200 years ago than in the subsequent 150 years. Our results suggest that stand dynamics in the forests analyzed are driven by numerous events of limited spatial extent and that stand-replacing disturbances are not necessary for the development of unimodal age structure.

Key message Based on the first dendroclimatological analyses of the thermo-Mediterranean tree Pyrus bourgaeana, the positive relationship between the growth and climate (i.e., precipitation) has strengthened in recent decades. Abstract The combined effect of climate change and habitat destruction and fragmentation threatens many plant populations and even entire communities in Mediterranean ecosystems. The Iberian pear, Pyrus bourgaeana Decne, a characteristic species of Mediterranean ecosystems, is threatened by both habitat and climate changes. We ask whether and how the growth of mature P. bourgaeana in the thermo-Mediterranean zone (i.e., altitude \700 m) has been affected by long-term climate changes during the last century in a fragmented landscape. Dendrochronological methods were used to find growth-climate relationships. We made the first dendroclimatological analyses and constructed a first 103-year tree-ring chronology of this species. The tree-ring series revealed large growth variability. We found a clear, strong relationship between tree growth and climate, with annual precipitation being the most important climate factor enhancing radial growth. Our results also showed that warm autumns and winters positively affect growth. There was no temporal stability in the relationship between tree growth and climate. The most general trend was in the relationship between annual precipitation and tree growth: the decrease of rainfall in the last decades of the twentieth century was associated with a constant increase of the correlation coefficient. Water accumulated in the soil in autumn and winter proved to be a key factor augmenting tree growth in the following vegetation period. The climate-growth relationship in P. bourgaeana has strengthened in recent decades apparently due to decreased precipitation levels.

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Metasequoia glyptostroboides is considered to be a species highly resistant to harmful environmental factors. For this reason it has been introduced to the cities. The climate of Krakow differs from that in its natural range in China. The research was focused on 40-year-old trees, planted in Kraków on fertile alluvial soils with a low level of ground water, in the vicinity of the steelworks. During the period of the highest level of air pollution in the 1970s and 1980s, the radial increment of investigated trees showed an increasing trend. At the end of the 1980s, when the emissions were reduced, a decreasing trend in radial growth was recorded. Throughout the entire period of their life the investigated trees have shown high homogeneity of short-term growth reactions. The sensitivity chronology of the trees was characterized by a high representativeness and a strong high-frequency signal. This may indicate that the investigated trees have shown a large sensitivity to climatic factors. The positive effect on the radial growth of Metasequoia had a cold September in the previous year, and also a cold January, April and May in the year of ring formation. Positive impact on the growth of trees had also the high precipitation occurring in April and August, as well as high air humidity in the spring of the year of ring formation. In the period 1974-2011 fifteen signature years were found. The analysis of the climatic conditions in these years confirms the results of the statistical analyses.

The relative importance of environmental factors and species pool in natural regeneration processes is still intensively disputed. Is environmental filtering especially important for species with higher requirements for temperature and soil fertility? Is the seed source limitation especially pronounced among tree species with lower dispersal abilities? Trees, seedlings and saplings measurements were conducted in 600 plots of 0.05 ha distributed in a regular grid in the Tatra Mountains (elevation range 817–1797 m a.s.l.). Boosted regression trees were used to analyse the relationships between the numbers of young trees, factors acting as environmental filters and the potential seed source availability. The most important factor affecting the distribution of young trees of most species was elevation; bedrock type was the second most important factor for Acer pseudoplatanus, while potential solar radiation was important for Sorbus aucuparia. The relationship between the presence of mature trees and abundance of young ones was strong in Fagus sylvatica, moderately strong in A. pseudoplatanus, and weak in Picea abies, Abies alba and S. aucuparia. The role of environmental factors in shaping the abundance of young trees varies strongly among species, while the seed source availability is very important for large-seeded trees.