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Delivering material selected for breeding purposes into the wild in the context of sustainable forest management might reduce the levels of genetic diversity of future forests in comparison to that of natural populations. Another consequence might be a reduction of their resilience under uncertain future climatic and socio-economic conditions if these new populations lack adaptability. Despite the long tradition of breeding activities in Europe, there is still a need to assess the impact of genetically enriched material on forests’ resilience. In this study, we address (1) the genetic diversity of selected material compared to its wild ancestors, and (2) how to enrich breeding material to support forests’ resilience under changing socio-environmental conditions. We analysed 16 study cases of selected material delivered from breeding activities in four European forest tree species (Pinus halepensis Mill., Pinus nigra J.F. Arnold, Pinus pinaster Ait. and Populus nigra L.) with different levels of breeding. To answer these two questions, we first assessed and compared the genetic diversity of selected material versus natural populations using both putatively neutral and adaptive (based on diverging selection) Single Nucleotide Polymorphisms (SNPs). We then suggest how to enrich these populations for resilience under future climatic conditions by defining a core collection for each species including material from populations that will likely disappear under future conditions. Thanks to the large SNP datasets available for our focal species, we were able to detect some trends in our data. Expected and observed heterozygosity values for selected populations were almost always identical. The selected material showed small but significant genetic differentiation from their original population and their inbreeding coefficient was generally lower. However, the level of genetic improvement (i.e. low vs high) was not correlated with the observed genetic differences between selected material and natural populations.The genetic characterization of natural populations distributed across the species range, and the future projection of their range stability, made it possible to identify core-collections that would significantly enrich breeding populations under uncertain future environmental conditions. This work was supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 676876-Gentree “Optimizing the management and sustainable use of forest genetic resources in Europe”; the Spanish Ministry of Science [Grant No RTI2018-094691-B-C32]. Peer reviewed 11 Pág.

Because forests provide a myriad of essential services to society, sustainable forest management that considers and promotes the multifunctional role of forests is of key importance. Understanding how forests have been and are being managed is essential to learn how current forest landscapes have been shaped and how management could be improved to better address all societal needs. Spain makes for an interesting case study due to its dramatic expansion in forest cover over the last 150 years following ambitious national reforestation and afforestation initiatives, as well as for its diversity of forest ecosystems and management approaches. However, a national-level assessment of such a development is currently missing. Therefore, our objective was to document and analyse the development of forest management practices in Spain since the mid-20th century. We developed narratives to describe the trends in 11 indicators of forest management decision-making and practices. Results show that while some decisions have evolved towards promoting multifunctionality (e.g., soil cultivation), others have intensified to maximize production at the expense of other ecosystem services (e.g., naturalness of tree species) and others have not changed much during the past 80 years (e.g., type of regeneration). The analysis also showed that some of the indicators have been conditioned by technological innovations (e.g., machine operation) and by the development of certain policies and legislation (e.g., the application of chemical agents). Based on these trends, we identified the main challenges that forest management in general, and in Spain in particular, may face as well as some decisions that may have to be reconsidered (cutting regime, tree maturity, naturalness of tree species) if the country wants to transition towards alternative silvicultural approaches that promote multifunctionality. In addition, a transition towards mixed-species, uneven-aged forests alongside with genetic improvement of tree species would also facilitate rising to one of the main challenges that forest management faces: to develop a climate-smart forestry that contributes to the mitigation of and adaptation to global change. SdM benfitted from a Serra-Húnter Fellowship provided by the Government of Catalonia. PJV contributed to this research as part of the GenTree project, which has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 676876. ME and SdM also contributed to this research as part of the SUPERB project, which has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 101036849.

Monospecific pine forests are widespread due to extensive afforestation efforts and natural colonization of abandoned croplands in the Mediterranean Basin. It was originally thought that pines would facilitate the natural colonization of native late-successional resprouter species (e.g., hardwoods), but these species can be compromised if competition with pines outweighs their facilitative effect on these hardwood species. Managing the density or canopy cover of these widespread pine forests can potentially provide some “optimum” balance between facilitation and competition to maximize success in the introduction of late successional species while maintaining a tree stratum. We tested the response (survival and growth across 10 years) of six resprouter species covering a wide range of plant functional strategies, from drought-tolerant sclerophyllous shrubs and trees to malacophyllous drought-sensitive trees, across an experimental gradient of Aleppo pine canopy cover. Seedling performance varied according to the functional strategy, pine cover and time. High pine cover generally enhanced seedling survival, whereas moderate pine cover generally enhanced seedling growth, although this response was modulated by the functional strategy of the seedling species. Interactions between pines and seedlings were only detectable 2–3 years after plantation, increasing in intensity with time. The latter highlights the need of medium to long-term studies to evaluate plant-plant interactions in these water-limited environments with slow successional trajectories. Our results could be attributed to the shade tolerance of most of the introduced trees, combined with their low tolerance to the combination of high sunlight radiation and drought. We found an optimal pine cover of ca. 50% (equivalent to 300–400 trees/ha) in which both survival and growth of late successional species can be maximized, which help to select best locations for more efficient reforestation programs and set a threshold value to decide whether or not to perform tree thinning to enhance ecosystem diversity and, subsequently, resilience. The study was funded by the FUME (EU FP7-Environment, GA. 243888), SURVIVE-2 (CGL2015-69773-C2-2-P MINECO/FEDER) and INERTIA (PID2019-111332RB-C22) projects, from the Spanish Government and IMAGINA project (PROMETEU/2019/110) from Generalitat Valenciana. L.M. was supported by the Spanish MICINN (PTA2019-018094). S.S. was supported by the Ramón y Cajal fellowship (RYC-2016-20604) and the FOBIASS project (RTI2018-098895-A-100), both from the Ministry of Science and Innovation. CEAM foundation is funded by Generalitat Valenciana.

Wood resources have been essential for human welfare throughout history. Also nowadays, the volume of growing stock (GS) is considered one of the most important forest attributes monitored by National Forest Inventories (NFIs) to inform policy decisions and forest management planning. The origins of forest inventories closely relate to times of early wood shortage in Europe causing the need to explore and plan the utilisation of GS in the catchment areas of mines, saltworks and settlements. Over time, forest surveys became more detailed and their scope turned to larger areas, although they were still conceived as stand-wise inventories. In the 1920s, the first sample-based NFIs were introduced in the northern European countries. Since the earliest beginnings, GS monitoring approaches have considerably evolved. Current NFI methods differ due to country-specific conditions, inventory traditions, and information needs. Consequently, GS estimates were lacking international comparability and were therefore subject to recent harmonisation efforts to meet the increasing demand for consistent forest resource information at European level. As primary large-area monitoring programmes in most European countries, NFIs assess a multitude of variables, describing various aspects of sustainable forest management, including for example wood supply, carbon sequestration, and biodiversity. Many of these contemporary subject matters involve considerations about GS and its changes, at different geographic levels and time frames from past to future developments according to scenario simulations. Due to its historical, continued and currently increasing importance, we provide an up-to-date review focussing on large-area GS monitoring where we i) describe the origins and historical development of European NFIs, ii) address the terminology and present GS definitions of NFIs, iii) summarise the current methods of 23 European NFIs including sampling methods, tree measurements, volume models, estimators, uncertainty components, and the use of air- and space-borne data sources, iv) present the recent progress in NFI harmonisation in Europe, and v) provide an outlook under changing climate and forest-based bioeconomy objectives.

Abstract Short rotation plantations of willows (Salix spp.) have high biomass production potential in many parts of the world, and may frequently support ecosystem services related to nutrient cycling. A plantation management enhancing favorable environmental impacts that are conducive to maintaining ecosystem services is a main challenge in establishing sustainable biomass production systems. There is evidence supporting the hypothesis that biomass production and nutrient cycling can be increased by supporting ecosystem niche differentiation (complementarity) through enhancing the number of plant species or varieties grown in the stand. However, the specific trait values of the individual components (e.g., varieties) in a mixed community could also be more important than the community diversity per se. We assessed, at community level, the plant trait profiles related to growth and nitrogen (N) use for four different Salix varieties that were taxonomically distinct at species or genotype level (‘Bjorn’, ‘Jorr’, ‘Loden’, ‘Tora’) and field-grown in unfertilized plots of pure and mixed communities during one cutting cycle in Central Sweden. The aims were to use elements of functional growth analysis for exploring the mechanistic relationships between various traits related to growth and N use at stand level in our pure and mixed willow communities; and to address two hypotheses related to (i) the effect of diversity level on above-ground traits linked to growth, N uptake efficiency, N productivity and N conservation; and (ii) the influence of individual variety identities on the growth and N use traits observed in a mixture. Diversity level had no significant effect on the traits assessed here, and we thus found no evidence in support of our hypothesis that traits linked to growth, N uptake and use are significantly affected by the diversity level per se. In most but not all cases, the admixing effects on trait values were explained by the effects of the individual variety characteristics assessed in monocultures in combination with their relative share in the respective mixtures. The absence or presence of individual varieties strongly affected community-averaged (stand level) trait values. Therefore, the design of desirable variety mixtures is suggested that combine, for example, the high nutrient conversion efficiency that certain varieties achieve in mixed stands with the specific nutrient acquisition characteristics of other varieties.

Increasing evidence supports that canopy richness favors multifunctionality in European forests. Given that recruitment represents one of the main demographic bottlenecks in plant communities, the provision of similar levels of forest functioning in the future will depend on successful natural regeneration in the present. Here, we evaluated whether canopy diversity enhances recruitment (abundance and richness) by providing a more diverse seed supply and a more heterogeneous environmental context; or, alternatively, if post-dispersal environmental filters outweigh these expected positive effects. For this purpose, we used a large-scale European platform comprising 173 forest plots that follow a canopy species richness gradient (from monoculture to mixed plots up to 5 tree species) in five forest types from Mediterranean to boreal forests. Despite that canopy diversity promoted a more diverse seed supply and a more heterogeneous light environment, this did not translate into a richer or more abundant community of recruits. In fact, we found an important uncoupling in species composition between recruitment and canopy layers. Our results suggest that strong post-dispersal filters, mediated by an interaction between seed size and latitude, drive this mismatch. Large-seeded species were over-represented in the recruitment at both extremes of the European gradient (Mediterranean and boreal forests), while the opposite trend occurred at intermediate latitudes. Altogether, our work shows that preserving a more diverse canopy may not ensure successful recruitment, and advocates future studies analyzing the role of post-dispersal filters on the assembly of European forests. We are grateful to the FunDivEUROPE site managers for establishing and maintaining of the permanent plots. C.C.B. is beneficiary of a FPU grant funded by the Spanish Government (AP2010-5600). R.B. was funded by a Marie Curie IEF fellowship (FP7-PEOPLE-2011-IEF). This research was supported by the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 265171, and also from Spanish-funded project REMEDINAL TE-CM S2018/EMT-4338.

Fine roots (diameter ≤ 2 mm) contribute significantly to the forest carbon cycle and are essential for resource acquisition from the soil. We conducted a study to assess the relationships between tree and ground vegetation fine root biomass and tree species diversity (monocultures compared to 2–5 species mixtures), conifer proportion and other site factors (stand basal area, soil carbon stocks and C:N ratio) in the six major European forest types, boreal forest in Finland, temperate forests in Poland, Germany and Romania, thermophilous deciduous forests in Italy, and Mediterranean forests in Spain. We sampled the fine roots of trees and ground vegetation to the depth of 20 cm in the mineral soil and allocated the fine root biomass to individual tree species using near-infrared reflectance spectroscopy (NIRS). We did not find any general positive effects of tree species diversity on the fine root biomass of trees or ground vegetation across the forest types and tree species combinations. However, our results suggest that tree fine root biomass increases with tree species diversity in pure broadleaf forests, but not in pure conifer forests. Species diversity explained 7% of the variation in tree fine root biomass in the broadleaf stands. The narrow tree species diversity gradient (1–2 species) in the conifer forests compared to the broadleaf forests (1−4) may have decreased the probability of conifer species combinations with below-ground functional traits conducive to over-yielding. Some evidence of diversity-mediated changes in the vertical rooting patterns of broadleaf trees and ground vegetation were found within the entire organic and 0–20 cm mineral soil layer although the weighted mean depth of fine root biomass was not affected. Negative diversity effects were found in the organic layer and positive diversity effects in the 0–10 cm mineral soil layer for broadleaf tree fine root biomass. Diversity effects were negative for ground vegetation fine root biomass in the 0–10 cm mineral soil layer. There was a general positive effect of conifer proportion on total fine root biomass in the organic layer, but not in the mineral soil layers. In general conifer proportion and site factors explained more of the variation in tree fine root biomass than tree species diversity. More research covering the annual variation in fine root biomass and deeper soil layers is needed before recommending managing species-rich forest for increasing below-ground biomass and carbon pools. The research received funding from the European Union Seventh Framework Program (FP7/2007–2013) under grant agreement n° 265171, FunDivEUROPE. Peer Reviewed