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Aim: Dead wood‐inhabiting bryophyte communities are formed by several important factors. Besides the amount, quality and continuity of the substrate, there are also external factors indirectly influencing their structure. One of the most important is local microclimate. This fact has been recognized by many previous authors, yet studies exploring the direct effect of the microclimate on epixylic bryophytes are still sparse. Based on directly measured values of local temperature, air humidity and canopy openness (CO), we explored the associations between microclimate and epixylic bryophyte communities. Location: Old‐growth mixed Fagus sylvatica‐Abies alba montane forest in the Czech Republic (West Carpathians). Methods: The associations between microclimate and bryophyte communities were studied on 61 large logs of Abies alba in advanced decay stage. Air temperature and humidity were measured in three periods of the year 2017, CO was measured in leafless and leaf‐on periods. Water potential (Ψ) values were calculated from the data. The importance of the seasons was compared, the effect of microclimate variables on the species composition of logs was explored by canonical correspondence analysis. The effect on total cover and species richness was analyzed by linear models. Results: Our analysis revealed a clear relationship between the communities and the microclimatic gradient. The most important factors for bryophyte composition were the spring and summer water potential and CO in the leaf‐on period. Total species richness and cover increased with increasing water potential (relatively cool and humid conditions). Also, the appearance of sensitive epixylic specialists (mainly liverworts) was positively correlated with these microclimatic conditions. On the other hand, species more tolerant to desiccation preferred logs with a drier and warmer microclimate. Conclusions: Comparing logs with similar physical properties but different microclimates, we confirmed that epixylic bryophyte communities are significantly associated to microclimatic conditions in natural temperate forest. [ABSTRACT FROM AUTHOR]

Questions: How have tree growth and growth trends varied in structurally complex old‐growth forests? What determines this variation and how this differs among species? Location: Natural boreal old‐growth forests, northern Finland. Methods: We sampled trees over 10‐cm diameter on 48 randomly located 0.1‐ha plots in three landscapes and compiled a data set of 1,565 trees including all three main species, and a full range of sizes and competitive states in northern boreal old‐growth forests. We extracted tree ring samples from every tree and used ring widths to reconstruct tree sizes and their neighbourhood for the past 50 years for Pinus sylvestris and Picea abies, and 30 years for Betula pubescens. We used mixed‐effects models to study variation in tree growth. In the models, we used annually varying environmental variables, forest and tree structural variables and site variables as predictors. We also measured soil hydraulic properties for a water balance model to specifically include soil moisture deficits as predictors. Results: Tree growth rates had increased during the analysis period for all three species, with the highest increases for P. sylvestris and B. pubescens. All three species grew well during warm summers, but P. sylvestris and P. abies growth was also negatively influenced by soil moisture deficits. Competition in these sparse forests had a small influence on growth. However, its influence increased over time. Conclusions: The trees showed positive growth trends, but the increasing competition means that such strong positive trends are unlikely to continue over the long term. For year‐to‐year variability, negative influence of droughts implied that increasing temperatures are not only beneficial to tree growth even in these high‐latitude forests. Overall, the findings demonstrate the site‐ and species‐dependent complexity in tree responses to environmental and structural changes we may expect in the future. Tree growth rates in the northern boreal old‐growth forests in Finland showed increasing trends in the recent decades. However, at annual resolution, droughts negatively influenced the growth of Norway spruce and Scots pine, implying that even in these high latitude (67°N) forests the benefits of increasing temperatures to tree growth are limited. [ABSTRACT FROM AUTHOR]

Brzeziecki et al. 2016 ( Journal of Vegetation Science 27: 460-467.) describe a decrease in population densities and proportion of younger individuals for several tree species in permanent research plots in the core zone of the Białowieża National Park. They attribute insufficient tree recruitment inter alia to the strict protection. Although the authors performed a thorough analysis of tree population dynamics, the scales of the study mean that their far-reaching conclusions on the causes and consequences of the lack of demographic equilibrium cannot be supported by the data. The inadequate spatial and temporal scales of the study did not allow for the observation of representative population dynamics. Furthermore, they did not compare the results obtained in the strictly protected area with known demographic dynamics of trees in surrounding managed forests or under other forms of nature conservation. Looking from the wider ecosystem perspective, it is clear that strict protection is not a cause for concern and, instead, that such a near-natural forest manifests population dynamics at rather larger scales. [ABSTRACT FROM AUTHOR]

Questions What are the stand development patterns and successional processes occurring in a Quercus petraea-Fagus sylvatica old-growth forest? Do these two sympatric species have different recruitment and canopy accession strategies? How do they respond to disturbance? Location Old-growth Q. petraea- F. sylvatica forest in Runcu Grosi Natural Reserve, Romania. Methods Increment cores were taken from 110 similarly sized pairs of standing dead and living sessile oak trees, and additionally from the 110 most competitive neighbouring living beech trees, growing in the best-preserved part of the reserve. Release events were detected using the boundary line method. Recruitment and canopy accession strategies were defined using tree juvenile growth rate, overall growth patterns and the presence or absence of a major crown release. Results Sessile oak establishment occurred between 1800 and 1859, while beech have regenerated continuously, with greater in-growth after 1860. Tree recruitment followed species-specific requirements, with most sessile oak having a gap origin (82%) and many beech regenerating in the understorey (41%). Release events occurred continuously during the period analysed (1820-2003), but the percentage of trees per decade that showed releases was <15%. A larger number of releases were recorded in beech compared to sessile oak. Living and dead sessile oak originated under similar conditions, but after the 1900s they experienced different canopy disturbances regimes. Conclusions The investigated stand appears to originate after a large-scale disturbance that promoted sessile oak recruitment. Thereafter, regular small-scale disturbances favoured beech, which became a competitor to sessile oak and achieved faster growth despite a less favourable initial canopy position. Mortality started to occur in oak. Stand maturation and increasing competition could favour the occurrence of large-scale windthrow, which would again promote sessile oak. [ABSTRACT FROM AUTHOR]

Currently, Brzeziecki et al. 2016 ( Journal of Vegetation Science 27: 460-467.) are using data from permanent study plots established in 1936 in Białowieża National Park ( NE Poland) to develop theoretical equilibrium tree size distributions and to then compare modelled and actual distributions with a view to assessing the population dynamics of the species involved. As part of their discussion, the authors address the question of possible consequences for the overall diversity of forest ecosystems under strict protection if long-term trends relating to tree population densities and size structures are maintained. In the overall context of the above, the goal of the present paper is to respond to Jaroszewicz et al. ( Journal of Vegetation Science 28: 218-222.) who suggest that the paper of Brzeziecki et al. (2016) is not representative for the whole Białowieża National Park, and that - in this connection - strict protection should not be seen as a cause for concern. In this paper, we show that the data analysed by Brzeziecki et al. (2016) adequately characterize conditions in the wider Park. We also point out that the thorough scientific understanding of the long-term dynamics of woodland communities under strict protection should indeed be taken into account as efforts are made to arrive at an effective conservation strategy capable of ensuring that the uniquely valuable features of the Białowieża Forest are retained. [ABSTRACT FROM AUTHOR]

Questions: Does the size structure characterizing particular tree species in natural forest stands converge towards a steady state? What is the main reason for departures of observed tree size distributions from equilibrium models? What is the consequence of long-term strict protection for the demography of tree species and the conservation of associated biota? Location: Stands of natural forest in Białowież a National Park (NE Poland) that have been under strict protection for about 90 yr. Methods: Data on recruitment, growth and mortality of approximately 10 000 trees representing 11 species (aspen, birch, alder, pine, oak, maple, ash, elm, spruce, lime and hornbeam), from seven replicated surveys of five permanent monitoring plots (total size = 15.44 ha), established in 1936, were used to derive theoretical, species-specific equilibrium distributions as a basis for evaluating the demographic changes of the species involved. Results: Over a monitoring period of 76 yr, there were strong downward trends in the population densities of several tree species of different successional status and light requirements. A vast majority of the conspecific equilibrium curves, modelled on the basis of growth and mortality data, revealed a 'rotated sigmoid' shape when plotted in semi-log plots. In contrast to these equilibrium curves, the observed tree size distributions of most species were unimodal, at both the beginning and the end of the study period. Departures between theoretical and observed distributions increased over time, particularly for shadeintolerant and intermediate species. Conclusions: The populations of several tree species occurring in the Białowież a National Park are demographically unstable - a fact reflected in large and steadily increasing differences between theoretical and actual tree size distributions. The main reason for this are the insufficient recruitment rates typical of most species. Some tree species may very soon disappear almost entirely, and this will certainly lead to far-reaching changes in the functioning of local forest communities. Among other consequences, the current demographic trends, as observed for Białowieża tree species, are very likely to have a strong effect on the long-term survival of numerous forest organisms (such as insects, fungi, lichens, etc.), which depend, directly or indirectly, on the presence and balanced demography of particular tree species. [ABSTRACT FROM AUTHOR]

Questions What are the differences between the tree spatial patterns ( TSP) of various recruit and mortality waves in alluvial hardwood forests and mountain fir-beech forests? Are there any statistically significant differences between the mean TSP of these forest types? Are these differences stable over time? Location Alluvial floodplain forests at the confluence of the Morava and Dyje rivers, and mountain fir-beech forests in the Outer Western Carpathians, Czech Republic. Methods In both forest types, seven 2-ha rectangular plots were analysed. The pair correlation function g( r) was used to describe tree density variability of trees with DBH ≥ 10 cm. The analyses were carried out for data sets from the 1970s, 1990s and 2000s. A bootstrap method was used to test for significant differences between the mean values of g( r) from alluvial forests and from fir-beech forests. Results Recruits in mountain fir-beech forests revealed consistent clustering to at least 5 m. In alluvial hardwood forests, recruits also showed random distribution as well as occasional regular distribution at distances over 20 m. Bootstrap significance tests revealed significant differences between the mean values of g( r) for alluvial forests and fir-beech forests. Alluvial floodplain forests showed statistically significant stronger clustering up to a distance of 4 m in all study periods. At distances over 20 m, mountain fir-beech forests demonstrated stronger clustering. In the 1970s, this was statistically significant only at a distance of 32 m, but in the 2000s, it was at intervals of 22-30 and 34-38 m. Conclusions The methods of data analysis in this study enabled us to find significant features of TSP at finer resolution than the common resulting trichotomy of univariate analysis: clustering, randomness and regularity. We believe that, on the basis of detailed spatial analyses, it is possible to create a TSP model that reflects the typical features of particular forest types. [ABSTRACT FROM AUTHOR]