• Key message Parametric indirect models derived from stem analysis of dominant trees were more robust than rule-based machine learning techniques for predicting Site Index of Scots pine stands as a function of climate. • Context The uncertainties derived from climate change make it necessary to develop new methods for representing the relationships between site conditions and forest growth. • Aims

• Key message Pronounced additive genetic variation and high narrow-sense heritability for lesion length caused by Neonectria neomacrospora were found in a Nordmann fir progeny test. Significant inbreeding depression was detected in traits important for Christmas tree production. Recurrent selection for multiple traits would be successful for Christmas tree quality traits. • Context The fungal pathogen

• Key message The browsing level of oak (Quercus petraea and Quercus robur) and fir (Abies alba) provided only a rough estimate of the expected regeneration success. Thus, it cannot be recommended as a standard measurement to predict forest development, unless the number of saplings and the height of those saplings are considered. • Context Browsing by large herbivores may affect regeneration success

• Key message Canopy closure and stand age significantly affected the litter decomposition. Therefore, stand-specific decomposition constants (k) should be calculated in forest carbon models for more accurate carbon budget estimation. Furthermore, to reduce the carbon release from decomposing litter, regeneration cutting should be carried out at later ages, and heavy thinning should not be implemented

• Key message Invasive tree species alter taxonomic diversity and functioning of forest shrub layers: Prunus serotina increases shrub layer biomass two to three times but decreases its biodiversity, Robinia pseudoacacia slightly increases shrub layer biomass and has no effect on its biodiversity, while Quercus rubra both biomass and biodiversity of the shrub layer. • Context Although the impact of

• Key message Errors in forest stand attributes can lead to sub-optimal management prescriptions concerning the set management objectives. When the objective is net present value, errors in mean diameter result in greater losses than similar errors in basal area, and underestimation greater losses than overestimation. • Context Errors in forest inventory data can cause inoptimality losses in the objectives

The original article was published with an erroneous affiliation details for co-author, David J. Lee. The correct affiliation for the author is Forest Industries Research Centre, University of the Sunshine Coast, Locked Bag 4, Maroochydore DC, QLD, 4558, Australia. The original article has been corrected

• Key message Sampling needs differ by forest type for timber inventory and structural complexity metrics. We demonstrate in a typical mixed Eastern Hardwoods forest that optimal sampling of timber inventory metrics and spatially explicit structure indices may be achieved in one large plot plus a cruise for large diameter trees, but accurately capturing inventory metrics may not be possible with sparse

• Key message Wavy grain, a rare figure type of wood, leads to highly priced timber in Acer pseudoplatanus L. The influence of this trait on growth performance and its causes are not known. Analyzed wavy and straight grain sycamore maple progenies show comparable growth performance in a field trial. Stability of wavy grain after vegetative propagation is confirmed and genetic inheritance indicated

• Key message Ash dieback decreases individual reproductive success of ash trees leaving healthy ash overrepresented as seed and pollen parents for next-generation seedlings. Substantial gene flow over hundreds of meters combined with superior fertility of healthy trees creates optimism for the species’ future in European forests. • Context Hymenoscyphus fraxineus is causing high mortality in European

• Key message Total fidelity value index can be used for the assignment of new relevés to existing vegetation units and it can be used to refine classifications derived from unsupervised clustering. • Context Diagnostic species is an important concept in vegetation classification. Apart from its usefulness to characterize species niche preferences, the diagnostic species concept is used in vegetation

• Key message We successfully transformed Pinus sylvestris yield tables into diameter distribution models. The best results were obtained with the parameter recovery method based on both mean and quadratic mean diameter, which explained 70% of the variability of frequencies by diameter classes and provided better results in the analysis of errors. On the other hand, the method based on stand density

• Key message Litter trap is considered the most effective method to quantify seed production, but it is expensive and time-consuming. Counting fallen seeds using a quadrat placed on the ground yields comparable estimates to the litter traps. Ground quadrat  estimates derived from either visual counting in the field or image counting from quadrat photographs are  comparable, with the latter being also

• Key message Mechanisms controlling germination of > 2600 Arecaceae species adapted to the tropical forests are not clearly understood. This contribution underpins the notion that the coexistence of dormancy and desiccation sensitivity in some Arecaceae species could significantly affect the germination ecology. Although the evolutionary and ecological significance behind this occurrence is unknown

• Key message A recent paper by Ceccherini et al.( 2020a ) reported an abrupt increase of 30% in the French harvested forest area in 2016–2018 compared to 2004–2015. A re-analysis of their data rather led us to conclude that, when accounting for the singular effect of storm Klaus, the rate of change in harvested area depended on the change year used to separate the two periods to compare. Moreover

• Key message A novel non-destructive method has been developed to predict modulus of elasticity (MOE) of logs using measurements taken from cores extracted from discs. The trees were felled and cut into logs to allow validation of our method; however, similar results would be obtained if the cores were extracted from standing trees. The method shows that a single core from breast height is sufficient

• Key message A multi-criteria analysis can be an interesting tool to assess the effects of silvicultural treatments on ecosystem services supply. In the degraded forests, thinning has a positive effect on the provision of ecosystem services such as timber and bioenergy production, climate change mitigation, and recreational attractiveness. • Context The Millennium Ecosystem Assessment highlights the

• Key message Decomposition of forest herb species litter was not always completed in less than a year and was not always faster than decomposition of tree leaf litter in an oak-hornbeam forest in Western Poland. Litter decomposition of herbaceous plants is connected with their life strategy and functional traits of their leaves. • Context Forest understories are frequently ignored in ecological research

•Key message An ensemble modelling approach was performed to predict the distributions of seven sympatric sclerophyllous oak species in the Hengduan Mountains of Southwest China. Spatial eigenvector filters revealed missing factors in addition to commonly used environmental variables, thus effectively improved predictive accuracy for the montane oak species. This study identified a richness center

Abstract Key message We modeled 10-year net stand volume growth with four machine learning (ML) methods, i.e., artificial neural networks (ANN), support vector machines (SVM), random forests (RF), and nearest neighbor analysis (NN), and with linear regression analysis. Incorporating interactions of multiple variables, the ML methods ANN and SVM predicted nonlinear system behavior and unraveled complex

Key message A piecewise polynomial function already used to represent the size-density trajectories of pure even-aged stands of beech, oak, and Douglas-fir proved its ability to represent the size-density trajectories of a new species, ash. The widespread ash dieback caused departures from the expected size-density trajectories. These abnormalities can be used to detect an extra level of mortality

Key message A novel multi-environment competition individual-tree mixed model resulted in better fit, and greater individual narrow- and broad-sense heritabilities than the model without competition, notably for traits showing competition. In multi-environment tests, the proposed model would allow tree breeders to select genotypes with the best performance in both additive direct and competition breeding

• Key message Non-selective thinning of a hybrid aspen coppice stands via corridor or cross-corridor cutting impacts residual trees differently depending on their competitive status. Suppressed residual trees’ metabolic profile indicates increased stress level, especially after cross-corridor thinning. • Context Early thinning with regular corridor harvests is proposed for the management of post-harvest

The original article was published with a small but significant mistake.

This correction stands to correct the listed errors in the original article:

Key message Climate change will induce a change in fire frequency in Mediterranean region and that could impact fire-adapted plant species. We showed that fire-related traits of some pine species are strongly related to other factors than fire but the recent fire history has nonetheless an impact on the variation of key traits for different fire adaptive strategies. Context In fire-prone Mediterranean

Key message Patterns of stem radial variations showed that Cedrus libani A. Rich. was less limited by summer drought than co-occurring Juniperus excelsa M. Bieb. Cedrus libani recovered faster from tree water deficit and showed significantly higher radial growth rates and annual stem increments than J. excelsa . However, the ability of J. excelsa to grow more hours per year may indicate a potential

Key message Unprecedented forest declines and diebacks are expected worldwide in response to global change. Insects can trigger or contribute to these disturbances, which can in turn have either beneficial or detrimental retroactive cascading effects on insect communities. However, we are still unsure of the effects that pests will have on these disturbances in the future, and new biodiversity and

• Key message Strong density differences were observed between stem wood at 1.30 m and other tree components (stem wood, stem bark, knots, branch stumps and branches). The difference, up to 40% depending on the component, should be taken into account when estimating the biomass available for industrial uses, mainly fuelwood and wood for chemistry. • Context Basic density is a major variable in the

This correction stands to correct the listed errors in the original article:

Key message This literature review identified the main factors for the success of different silvicultural approaches to regenerate sessile oak naturally and unveiled at the same time important knowledge gaps. Most previous studies were only short-term and restricted to a few factors and single locations. Hence, the findings of these studies are of limited explanatory power and do not allow to develop

Key message Dormancy in Arecaceae diaspores is due to underdeveloped embryos, therefore, morphological dormancy or morphophysiological dormancy. Consequently, claims such as external seed structures inhibit germination, embryos are fully developed at maturity, and underdeveloped embryo is not a form of dormancy are rejected, because embryo size of the diaspore at the time of dispersal was not taken

Key message Late-season extreme climatic events induced variations in wood density and extended growth for more than a month in 2016 in Juniperus przewalskii Kom. growing on the Northeastern Tibetan Plateau, suggesting extraordinary growth resilience of the species in response to short extreme events over the cold and arid region. Context Monitoring xylem formation (xylogenesis) during extreme meteorological

Key message French forests exhibit the fastest relative changes across Europe. Growing stock increases faster than area, and is greatest in low-stocked private broadleaved forests. Past areal increases and current GS levels show positive effects on GS expansion, with GS increases hence expected to persist. Context Strong increases in growing stocks (GS) of European forests for decades remain poorly

Key message The precise demarcation and cross-dating of tree rings in Aspidosperma tomentosum Mart., a valuable timber species in the tropical dry forests of South America, were used to develop the first well-replicated chronology covering the period 1843–2015. A. tomentosum Mart. tree growth is strongly regulated by soil water availability prior to and during the current growing season. In the context

Key message The potential of airborne laser scanning (ALS) and multispectral remote sensing data to aid in generating improved wind damage risk maps over large forested areas is demonstrated. This article outlines a framework to generate such maps, primarily utilizing the horizontal structural information contained in the ALS data. Validation was done over an area in Eastern Finland that had experienced

Key message To be useful for silvicultural and forest management practices, the models of Site Index (SI) should be based on accessible predictor variables. In this study, we used spatially explicit data obtained from digital elevation models and climate data to develop SI prediction models with high local precision. Context Predicting tree growth and yield is a key component to sustainable forest

Key message In recent decades, there has been a decline in growth in a rear-edge broadleaf forest of Fagus sylvatica , Quercus petraea , and Q uercus pyrenaica . Although temperatures have been rising due to climate change, the observed decline in growth was mainly attributed to increased density and competition between trees since the cessation of traditional uses such as logging in the 1960s. Context

Key message Different tree species have dissimilar capacities to sequester soil organic carbon (SOC). Deciduous broadleaved trees show the most stable increase in SOC stock after afforestation than other tree species, while sempervirent conifer trees show the lowest rate of SOC stock change. Sempervirent broadleaved trees show the greatest increase in SOC stock 20 years after afforestation. Context

Key message Discovery of the first case of allotriploid juniper in a wild population in the French Alps where the parental species occurs in sympatry. Context Interspecific hybridization and polyploidy are important evolutionary phenomena in vascular plants. Natural hybridization between species living in sympatry can sometimes occur. Less frequent are successful hybridizations between species having

Key message On the selected sites in the investigated Oriental beech ( Fagus orientalis L.) dominated forests in Iran with an extensive individual tree selection system, tree microhabitats (MH) are more influenced by tree level factors such as tree species and DBH than by plot level factors such as plot basal area or size and species diversity. Context Despite the ecological importance of tree microhabitats

Key messageTree structure equations derived from pipe model theory (PMT) are well-suited to estimate biomass allocation in Scots pine ( Pinus sylvestris L.) and Norway spruce ( Picea abies [L.] Karst.). However, age dependence of parameters should be accounted for when applying the equations. ContextPipe model theory-based (PMT-based) structure equations have been incorporated in many process-based

Key message The important anatomical changes in tension wood, e.g., the high fiber ratio and rich mesopores, did not significantly increase the air and nitrogen flow; thus the gas permeability in the longitudinal direction of poplar ( Populus deltoides CL.’55/65′) tension wood is actually affected by the cell tissue macroporous porosity. ContextGas permeability is one of the most important physical

Key message This synthesis of the literature on incorporation of genetic gain into growth and yield models reveals a fundamental challenge associated with the rapid progress in genetics and breeding and limited empirical data on improved stands. Model improvements depend on a better understanding of both the biological basis for gain and of interactions between genetic and non-genetic factors on gain

• Key message This special issue gathers articles arising from the ERA-NET BiodivERsA3 research project “Unraveling the Potential of Spontaneous Forest Establishment for Improving Ecosystem Functions and Services in Dynamic Landscapes (SPONFOREST)”. Using a broad spectrum of research approaches, they provide detailed insights into how new forest stands establish and which consequences the establishment

Key message Radial growth in a group of Pinus radiata D. Don. trees varies in magnitude around the circumference and follows synchronous but arrhythmic dynamics. ContextEccentric and irregular girth growth is typically associated to specific growth responses, but it is generally assumed to be small or absent during normal development. The dynamics by which excess growth is formed are unclear. AimsThe

Key message Decline can affect the structure, resources, and microclimates of the forest canopy, and potentially have cascading effects on canopy-dwelling species. Our survey shows that an oak decline can promote saproxylic beetles, especially xylophagous ones, and generalist phyllophagous weevils. However, it negatively affects specialist leaf-eating species and has no effect on seed-eating weevils

Key message We examined the accuracy of the stand attribute data based on airborne laser scanning (ALS) provided by the Finnish Forest Centre. The precision of forest inventory data was compared for the first time with operative logging data measured by the harvester. ContextAirborne laser scanning (ALS) is increasingly used together with models to predict the stand attributes of boreal forests. The

Key messageStructural and ultrastructural traits of leaf xylem vary among European beech ( Fagus sylvatica L.) provenances in relation to climate. High tracheary element lumen area was observed in central Europe and decreased towards the range margins, while tracheary element density displayed opposite trend. Leaf anatomy and xylem cell-wall deformation were associated with climate continentality at

Key messageAnalyses of dendrochronological data from 15 recently established tablished stands of pedunculate oak (Quercus robur L.) revealed that functions describing potential tree growth in the absence of neighbours varied more between stands than functions describing competitive effects of conspecific neighbours. This suggests that competition functions can more easily be transferred among stands

Key message Faced with wicked problems such as climate change, managers of complex forest social-ecological systems require more than experimental sciences alone. Yet, mitigation and adaptation studies underuse social sciences in forest research, as shown here with the French case study. Therefore, we stress the value of social sciences for forest researchers, and extend this reflection to research

Key message NAC transcription factors may play important roles in the biological processes in Persian walnut. A total of 102 JrNAC s were identified in Persian walnut. The conserved domains, transcriptome profile, expression analysis, and interaction network suggest that JrNAC1-4 plays potential roles in Persian walnut flowering development. Context NACs are plant-specific transcription factors that

Key message In older, unlogged rainforest of Hainan Island, China, leaves of saplings were larger, and fine root systems of saplings were thicker with fewer root tips than in historically logged areas. These results were consistent among 15 Angiosperm lineages, even though families differed widely in their leaf and root traits. ContextHow plant organ morphologies vary with environment is key for inferring

Key messageFew studies have linked the origin of dispersed tree seeds with their post-dispersal fate. We show that habitat-dependent mortality in a pedunculate oak ( Quercus robur L.) seedling cohort reshapes the effective fecundity of individual mother trees but has little effect on the cohort’s genetic diversity. ContextInitial tree recruitment plays a key role in forest regeneration, yet little

Key message Centenary forest statistics informing major attributes of French forests were digitized, checked for consistency, and used to infer forest dynamics. Comparison to forest inventory data highlights increases in forest area and tree diversity, and substantial maturation of forests. Dataset access at https://doi.org/10.5281/zenodo.3739458 ContextThe history of European forest dynamic remains

Key message National Forest Inventories (NFIs) hold promise for monitoring and valuing of non-productive forest functions, including social and recreational services. European countries use a range of methods to collect social and recreational information within their NFI methodologies. Data collected frequently included general and recreation-specific infrastructure, but innovative approaches are

Key message A moderate genetic diversity, the absence of a significant genetic differentiation between wild and cultivated stands and a highly admixed genetic structure of sweet chestnut with two main clusters were observed in France using two different data sets with 10 and 18 microsatellites. ContextRenewed interest in European chestnut in France is focused on finding locally adapted populations

Key messageThis study presents an easy-to-apply variable probability sample design that is an efficient and cost-effective method to correct for local bias in regional LiDAR-assisted forest inventory estimates. This design is especially useful for small woodlot owners. ContextLight detection and ranging (LiDAR)-derived forest inventory estimates are generally unbiased at landscape levels but may be

Key messageThe wood of Pinus nigra populations planted in Portugal, comparatively to Pinus pinaster , has higher total extractive content, lower Klason lignin and H/G ratio, and similar mechanical properties, presenting advantages for industrial purposes. ContextP. nigra was used in the reforestation of mountainous areas in Portugal, but its wood chemical and mechanical properties were never studied

Key messageAn increase in the stiffness of lumber with a decrease in initial tree spacing was confirmed for Pinus patula Schiede ex Schltdl. & Cham. The underlying properties of microfibril angle, wood density and knot frequency explained 71% of the variation in lumber stiffness. Tree spacing also influenced wood properties independent of radial growth rate. ContextRapid growth rates and reduced harvesting