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Highlights • Basal area (BA) was correlated with macroclimatic gradients along the Carpathians. • Fine-scale variation of BA is linked to local disturbances. • Recent stationarity in stand BA implied despite disturbance related variability. • Instances of high recent mortality may indicate a departure from stationarity. Abstract Disentangling the importance of developmental vs. environmental drivers of variation in forest biomass is key to predicting the future of forest carbon sequestration. At coarse scales, forest biomass is likely to vary along major climatic and physiographic gradients. Natural disturbance occurs along these broad biophysical gradients, and depending on their extent, severity and frequency, could either amplify or dampen spatial heterogeneity in forest biomass. Here we evaluate spatial variation in the basal area of late-successional Picea abies (L./Karst.) forests across the Carpathian Mountain Range of central Europe and compare the roles of coarse-scale biophysical gradients and natural disturbances in driving that variation across a hierarchy of scales (landscapes, stands, and plots). We inventoried forest composition and structure, and reconstructed disturbance histories using tree cores collected from 472 plots nested within 30 late-successional stands, spanning the Carpathian Mountains (approximately 4.5 degrees of latitude). We used linear mixed-effects models to compare the effect of disturbance regimes and site conditions on stand basal area at three hierarchical scales. We found that the basal area of late-successional Picea abies forests varied across a range of spatial scales, with climatic drivers being most important at coarse scales and natural disturbances acting as the primary driver of forest heterogeneity at fine scales. For instance, the stand-level basal area varied among landscapes, with the highest values (48–68 m2 ha−1) in the warmer southern Carpathian Mountains, and lower values (37–52 m2 ha−1 on average) in cooler areas of the eastern and western Carpathians. Finer-scale variation was driven by local disturbances (mainly bark beetle and windstorms) and the legacies of disturbances that occurred more than a century ago. Our findings suggest that warming could increase the basal area of northern sites, but potential increasing disturbances could disrupt these environmental responses. [ABSTRACT FROM AUTHOR]

Highlights • We compared Tree-related microhabitats (TreMs) in the Dinarides and Carpathians. • Density and diversity of TreMs were very high in beech dominated primary forests. • Geographical region was not a primary driver of TreM profile. • Tree species richness, DBH, and snags were the main drivers of TreM profile. • These findings may provide a benchmark for forest management practices. Abstract Tree-related microhabitats (TreMs) are important features for the conservation of biodiversity in forest ecosystems. Although other structural indicators of forest biodiversity have been extensively studied in recent decades, TreMs have often been overlooked, either due to the absence of a consensual definition or a lack of knowledge. Despite the increased number of TreM studies in the last decade, the role of drivers of TreM profile in primary forests and across different geographical regions is still unknown. To evaluate the main drivers of TreM density and diversity, we conducted the first large-scale study of TreMs across European primary forests. We established 146 plots in eight primary forests dominated by European beech (Fagus sylvatica L.) in the Carpathian and Dinaric mountain ranges. Generalized linear mixed effect models were used to test the effect of local plot characteristics and spatial variability on the density and diversity (alpha, beta, and gamma) of TreMs. Total TreM density and diversity were significantly positively related with tree species richness and the proportion of snags. Root mean square tree diameters were significantly related to alpha and gamma diversity of TreMs. Both regions reached similarly high values of total TreM densities and total TreM densities and diversity were not significantly different between the two regions; however, we observed between the two regions significant differences in the densities of two TreM groups, conks of fungi and epiphytes. The density and diversity of TreMs were very high in beech-dominated mountain primary forests, but their occurrence and diversity was highly variable within the landscapes over relatively short spatial gradients (plot and stand levels). Understanding these profile provides a benchmark for further comparisons, such as with young forest reserves, or for improving forest management practices that promote biodiversity. [ABSTRACT FROM AUTHOR]

• First study in primary forest linking ≥250 yr. disturbance history to bird assemblage. • Bird assemblage composition was driven by disturbance related structure. • Disturbance induced forest change did not decrease bird diversity or abundance. Understanding the processes shaping the composition of assemblages in response to disturbance events is crucial for preventing ongoing biodiversity loss in forest ecosystems. However, studies of forest biodiversity responses to disturbance typically analyze immediate or short-term impacts only, while studies relating long-term disturbance history to biodiversity assemblage dynamics are rare. To address this important knowledge gap, we used a dendroecological approach to link natural disturbance history of 250 years (1750–2000) to structural habitat elements and, in turn, to breeding bird assemblages. We used data collected in 2017 and 2018 from 58 permanent study plots within 10 primary spruce forest stands distributed across the Western Carpathian Mountains of Europe. This dataset contained breeding bird counts and environmental variables describing forest density, tree diameter distribution, tree height, tree microhabitats, deadwood quantity and quality, and regeneration. Bird assemblages were significantly influenced by forest structure which was in turn shaped by disturbance dynamics (disturbance frequency, time since the last disturbance and its severity). Early successional species associated with more open habitats were positively influenced by disturbance-related structure (i.e. deadwood-related variables, canopy cover), while some species responded negatively. At the same time, overall abundance, species richness and Shannon diversity of the bird assemblage remained unchanged under variable disturbance histories. Our results support a view of primary spruce forests as a highly dynamic ecosystem, harbouring populations of bird species at all stages of succession despite significant structural changes and shifting patch mosaics over time due to natural disturbances. [ABSTRACT FROM AUTHOR]