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Abstract Key message We found a significant increase in the latewood density of European beech, and a decrease in the latewood and mean wood density of silver fir and Norway spruce in European mountain forests over the period 1901–2016. In the past century, drought did not directly influence the wood density trend of the three studied species. However, for both fir and spruce, drought indirectly affected the mean wood density via changes in the latewood to earlywood ratio, i.e., in the case of extreme drought, trees with high values of latewood to earlywood ratio experienced a slight attenuation in the declining trend of their mean wood density. Context Century-long wood density measurements can provide novel information on tree response to climate change and the carbon sequestration potential of forest ecosystems. Still, the knowledge about long-term changes in wood density of European beech (Fagus sylvatica L.), silver fir (Abies alba Mill.), and Norway spruce (Picea abies (L.) H.Karst.) in European mountain forests needs to be further explored. Aims We assessed long-term changes in tree-ring mean wood density, earlywood density, and latewood density in trees of the three species between 1901 and 2016. We investigated the influence of endogenous factors (i.e., tree-ring width, current tree diameter, and latewood to earlywood ratio) and drought events on wood density. Methods In total, 150 tree cores were sampled from mountain forests in Bulgaria, Bosnia and Herzegovina, Slovenia, Switzerland, and Germany. The mean, early, and latewood density of these samples were measured with the LIGNOSTATION™ system. To address our research aims, we applied a linear mixed-effect modelling approach using the data from 101 correctly cross-dated cores that spanned the entire period of analysis. Results In the absence of drought, the latewood density of European beech increased by 7.1%, the late and mean wood density of silver fir decreased by 16.8% and 11.0%, respectively, and the late and mean wood density of Norway spruce decreased by 16.1% and 7.2%, respectively, between 1901–2016. In the past century, drought influenced the trends of wood density through an effect mediated by changes in the latewood to earlywood ratio. Specifically, in cases of extreme drought, silver fir and Norway spruce trees with a latewood to earlywood ratio value 50% higher than the median experience a slight attenuation in the declining trend of their mean wood density, making the negative impact of drought marginally less severe. Conclusions Our findings have significant implications for the accuracy of carbon stock assessments, national greenhouse gas inventories, and the utilization of wood from the three species. Given the fact that changes in wood density follow species-specific patterns and the expectation of more frequent drought events in Europe, in the future, it is essential to build further tree-ring density time series for other species and sites to improve our understanding of how climate change alters wood density and carbon sequestration of forest ecosystems.

Climate change significantly alters species distributions. Numerous studies project the future distribution of species using Species Distribution models (SDMs), most often using coarse resolutions. Working at coarse resolutions in forest ecosystems fails to capture landscape-level dynamics, spatially explicit processes, and temporally defined events that act at finer resolutions and that can disproportionately affect future outcomes. Dynamic Forest Landscape Models (FLMs) can simulate the survival, growth, and mortality of (stands of) trees over long time periods at small resolutions. However, as they are able to simulate at fine resolutions, study landscapes remain relatively small due to computational constraints. The large amount of feedbacks between biodiversity, forest, and ecosystem processes cannot completely be captured by FLMs or SDMs alone. Integrating SDMs with FLMs enables a more detailed understanding of the impact of perturbations on forest landscapes and their biodiversity. Several studies have used this approach at landscape scales, using fine resolutions. Yet, many scientific questions in the fields of biogeography, macroecology, conservation management, among others, require a focus on both large scales and fine resolutions. Here, drawn from literature and experience, we provide our perspective on the most important challenges that need to be overcome to use integrated frameworks at spatial scales larger than the landscape and at fine resolutions. Future research should prioritize these challenges to better understand drivers of species distributions in forest ecosystems and effectively design conservation strategies under the influence of changing climates on spatially and temporally explicit processes. We further discuss possibilities to address these challenges.

Ecology and forestry sciences are using an increasing amount of data to address a wide variety of technical and research questions at the local, continental and global scales. However, one type of data remains rare: fine-grain descriptions of large landscapes. Yet, this type of data could help address the scaling issues in ecology and could prove useful for testing forest management strategies and accurately predicting the dynamics of ecosystem services. Here we present three datasets describing three large European landscapes in France, Poland and Slovenia down to the tree level. Tree diameter, height and species data were generated combining field data, vegetation maps and airborne laser scanning (ALS) data following an area-based approach. Together, these landscapes cover more than 100 000 ha and consist of more than 42 million trees of 51 different species. Alongside the data, we provide here a simple method to produce high-resolution descriptions of large landscapes using increasingly available data: inventory and ALS data. We carried out an in-depth evaluation of our workflow including, among other analyses, a leave-one-out cross validation. Overall, the landscapes we generated are in good agreement with the landscapes they aim to reproduce. In the most favourable conditions, the root mean square error (RMSE) of stand basal area (BA) and mean quadratic diameter (Dg) predictions were respectively 5.4 m2.ha-1 and 3.9 cm, and the generated main species corresponded to the observed main species in 76.2% of cases.

We studied the distribution, growth and regeneration of black locust in Bela krajina. We used Slovenia Forest Service data and additionally recorded data on regeneration. Data from the forest stand level were used to calculate the share of black locust in the stand volume and to develop distribution and regeneration maps. The radial and volume increment of black locust trees were calculated using individual tree data from permanent sample plots and compared to those of other frequent tree species. Regeneration was analyzed in detail using regeneration data obtained on randomly selected permanent sample plots. Black locust occurs on 6.6 % of the forest area in Bela krajina and is more abundant along forest edges outside of larger contiguous forest areas. The stand volume of black locust represents 3.5 % of the total stand volume. The radial and volume increment of black locust is higher than those of most other tree species commonly occurring with black locust in the stands. Black locust is expected to continue to expand in the future and should therefore be taken into account in forest management.