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Many studies show that mixed species stands can have higher gross growth, or so-called overyielding, compared with monocultures. However, much less is known about mortality in mixed stands. Knowledge is lacking, for example, of how much of the gross growth is retained in the standing stock and how much is lost due to mortality. Here, we addressed this knowledge gap of mixed stand dynamics by evaluating 23 middle-aged, unthinned triplets of monospecific and mixed plots of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) repeatedly surveyed over 6–8 years throughout Europe. For explanation of technical terms in this abstract see Box 1. First, mixed stands produced more gross growth (+10%) but less net growth (−28%) compared with the weighted mean growth of monospecific stands. In monospecific stands, 73% of the gross growth was accumulated in the standing stock, whereas only 48% was accumulated in mixed stands. The gross overyielding of pine (2%) was lower than that of beech (18%). However, the net overyielding of beech was still 10%, whereas low growth and dropout of pine caused a substantial reduction from gross to net growth. Second, the mortality rates, the self- and alien-thinning strength, and the stem volume dropout were higher in mixed stands than monospecific stands. The main reason was the lower survival of pine, whereas beech persisted more similarly in mixed compared with monospecific stands.Third, we found a 10% higher stand density in mixed stands compared with monospecific stands at the first survey. This superiority decreased to 5% in the second survey.Fourth, the mixing proportion of Scots pine decreased from 46% to 44% between the first and second survey. The more than doubling of the segregation index (S) calculated by Pielou index (S increased from 0.2 to 0.5), indicated a strong tendency towards demixing due to pine. Fifth, we showed that with increasing water supply the dropout fraction of the gross growth in the mixture slightly decreased for pine, strongly increased for beech, and also increased for the stand as a whole. We discuss how the reduction of inter-specific competition by thinning may enable a continuous benefit of diversity and overyielding of mixed compared with monospecific stands of Scots pine and European beech., The study received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No952314 and under the Marie Skłodowska-Curie grant agreement No 778322. The first author also wishes to thank the German ScienceFoundation (Deutsche Forschungsgemeinschaft) for funding the project “Structure and dynamics of mixed-species stands of Scots pine and European beech compared with monospecific stands; analysis along an ecological gradient through Europe” (# DFG PR 292/15-1). Felipe Bravo is grateful for Funds by the Junta de Castilla y León through the projects “CLU-2019-01 and CL-EI-2021-05 - iuFOR Institute Unit of Excellence” of the University of Valladolid and the co-financing by the European Regional Development Fund (ERDF “Europe drives our growth”). Miren del Río thanks for the support by the Spanish Ministerio de Ciencia e Innovación (# PID2021-126275OB-C21/C22). Dejan Stojanović thanks the Ministry of Education, Science and Technological Development of the Republic of Serbia for funding. Tzvetan Zlatanov thanks the Ministry of Education and Science of the Republic of Bulgaria (# DO1-405/18.12.2020 LTER-BG).

Low nutrient availability often limits productivity in northern forests. In a nutrient optimisation trial, we investigated the effects of fertilisation and irrigation on soil moisture, leaf area index (LAI) as well as height and radial growth in 25-year-old stands of pedunculate and sessile oak (Quercus robur L., Q. petraea (Matt.) Liebl.) growing on abandoned farmland in southwestern Sweden. Control (C), fertilisation (F), irrigation (I), and irrigation + fertilisation (IF) treatments were arranged in a randomized complete block design. End of growing season analysis of foliar nutrients guided the quantitative composition of next year's fertiliser mix. Volumetric soil moisture (VWC) was significantly higher in the I and IF treatments compared to the C and F treated stands of both oak species. We did not observe a fertiliser-related reduction in VWC (except for 2015, when VWC in F treated Q. robur stands was significantly lower than the control by about 18 %). This is in line with the unaffected LAI estimates (5.3-5.9) suggesting no stimulation of leaf production that could drive increases in transpiration with subsequent soil moisture depletion. There was no treatment x year interaction for any of the growth-related variables. Treatments had no significant effects on basal area growth, which increased annually by 1.72 and 1.54 m2 ha-1 on average for Q. petraea and Q. robur, respectively. Pre-treatment height differences in Q. petraea stands (7-12 % taller trees in the C and IF plots) persisted throughout the study resulting in significant effects, while no significant differences in height occurred in Q. robur. Periodic annual volume increment varied more strongly following drier periods but there were no significant differences among treatments.Our findings indicate that fertilisation causes no or only minor increases in oak water use, suggesting that nutrient addition in oak stands within this precipitation regime does not require simultaneous irrigation. Most importantly, our data implies that the soil nutrient legacies of past agricultural use suffice to maximise the productivity of oak stands on abandoned farmland typical of the main oak growing region in southwestern Sweden.

13 Pág., Forest stand and environmental factors influence soil organic carbon (SOC) storage, but little is known about their relative impacts in different soil layers. Moreover, how environmental factors modulate the impact of stand factors, particularly species mixing, on SOC storage, is largely unexplored. In this study, conducted in 21 forest triplets (two monocultures of different species and their mixture on the same site) distributed in Europe, we tested the hypothesis that stand factors (functional identity and diversity) have stronger effects on topsoil (FF + 0–10 cm) C storage than environmental factors (climatic water availability, clay + silt content, oxalate-extractable Al–Alox) but that the opposite occurs in the subsoil (10–40 cm). We also tested the hypothesis that functional diversity improves SOC storage under high climatic water availability, clay + silt contents, and Alox. We characterized functional identity as the basal area proportion of broadleaved species (beech and/or oak), and functional diversity as the product of broadleaved and conifer (pine) proportions. The results show that functional identity was the main driver of topsoil C storage, while climatic water availability had the largest control on subsoil C storage. Functional diversity decreased topsoil C storage under increasing climatic water availability, but the opposite was observed in the subsoil. Functional diversity effects on topsoil C increased with increasing clay + silt content, while its effects on subsoil C were negative at increasing Alox content. This suggests that functional diversity effect on SOC storage changes along gradients in environmental factors and the direction of effects depends on soil depth., The European Union and the National Fund for Scientific Research (Fonds de la recherche scientifique) of Belgium supported this research as part the ERA-Net SUMFOREST project REFORM–Mixed species forest management. Lowering risk, increasing resilience (www.reform-mixing.eu). The lead author was further supported by Université catholique de Louvain for covid-19-related delays of his PhD project. Some of the triplets were selected, established and measured with funding from the EuMIXFOR FP1206 Cost Action project. The Polish State Forests Enterprise also supported one of the Polish co-authors (Grant No: OR.271.3.15.2017). The Orléans site, OPTMix was installed thanks to ONF (National Forest Service, France), belongs to research infrastructure ANAEE-F; it is also included in the SOERE TEMPO, ZAL (LTSER Zone Atelier Loire) and the GIS Coop network.

Understanding structurally complex boreal stands is crucial for designing ecosystem management strategies that promote forest resilience under global change. However, current management practices lead to the homogenization and simplification of forest structures in the boreal biome. In this chapter, we illustrate two options for managing productive and resilient forests: (1) the managing of two-aged mixed-species forests; and (2) the managing of multi-aged, structurally complex stands. Results demonstrate that multi-aged and mixed stand management are powerful silvicultural tools to promote the resilience of boreal forests under global change.

Since the beginning of the twentieth century, forest regeneration management and policy in the Nordic–Baltic region (Denmark, Sweden, Norway, Finland, Estonia, Latvia and Lithuania) have gone throu...

Heterogeneity of structure can increase mechanical stability, stress resistance and resilience, biodiversity and many other functions and services of forest stands. That is why many silvicultural measures aim at enhancing structural diversity. However, the effectiveness and potential of structuring may depend on the site conditions. Here, we revealed how the stand structure is determined by site quality and results from site-dependent partitioning of growth and mortality among the trees. We based our study on 90 mature, even-aged, fully stocked monocultures of Scots pine (Pinus sylvestris L.) sampled in 21 countries along a productivity gradient across Europe. A mini-simulation study further analyzed the site-dependency of the interplay between growth and mortality and the resulting stand structure. The overarching hypothesis was that the stand structure changes with site quality and results from the site-dependent asymmetry of competition and mortality. First, we show that Scots pine stands structure across Europe become more homogeneous with increasing site quality. The coefficient of variation and Gini coefficient of stem diameter and tree height continuously decreased, whereas Stand Density Index and stand basal area increased with site index. Second, we reveal a site-dependency of the growth distribution among the trees and the mortality. With increasing site index, the asymmetry of both competition and growth distribution increased and suggested, at first glance, an increase in stand heterogeneity. However, with increasing site index, mortality eliminates mainly small instead of all-sized trees, cancels the size variation and reduces the structural heterogeneity.Third, we modelled the site-dependent interplay between growth partitioning and mortality. By scenario runs for different site conditions, we can show how the site-dependent structure at the stand level emerges from the asymmetric competition and mortality at the tree level and how the interplay changes with increasing site quality across Europe. Our most interesting finding was that the growth partitioning became more asymmetric and structuring with increasing site quality, but that the mortality eliminated predominantly small trees, reduced their size variation and thus reversed the impact of site quality on the structure. Finally, the reverse effects of mode of growth partitioning and mortality on the stand structure resulted in the highest size variation on poor sites and decreased structural heterogeneity with increasing site quality. Since our results indicate where heterogeneous structures need silviculture interventions and where they emerge naturally, we conclude that these findings may improve system understanding and modelling and guide forest management aiming at structurally rich forests., This study was supported by the ERA-Net COFUND programme SUMFOREST, with the national funding organization Federal Ministry of Nutrition and Agriculture (REFORM, grant #2816ERA02S). The project has also received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No952314 and under the Marie Skłodowska-Curie grant agreement No 778322, and the 2017 - 2018 Belmont Forum and BiodivERsA joint call for research proposals, under the BiodivScen ERA-Net COFUND programme, with the national funding organization Federal Ministry of Education and Research (grant #16LC1805B). The German Science Foundation funded the project “Structure and growth of mixed Scots pine/European beech stands compared with pure stands analyzed along an ecological gradient through Europe” (grant #PR 292/15-1). H.P. and E.U. were additionally supported by the Bavarian Ministry of Nutrition, Agriculture and Forestry through the projects “Pine-spruce mixed stands in Bavaria” (grant #7831-20339-2012) and “Maintenance of the long term experimental plots in Bavaria (W07, #7831-26625-2017). M.d.R. and R.R.-P. were supported by the projects CLU-2019-01 - iuFOR Institute Unit of Excellence” of the University of Valladolid and VA183P20–SMART, funded by the Junta de Castilla and Leon (Spain) and co-financed by the European Union (ERDF “Europe drives our growth”). J.C. was supported by the National Agency of Agricultural Research (Project No. QK21020307). K.B. was supported by the Polish Government MNiSW 2018–2021 Matching Fund No. 117/H2020/2018. M.M. was supported by the Estonian Research Council grant (PRG1586) and Estonian University of Life Sciences projects number P180024MIME and P200029MIME. R.S. was supported by the Slovak Research and Development Agency project No. APVV- 19-0035.

In temperate Europe, oak-dominated forests are widespread, supporting high biodiversity and providing important ecosystem services. Insufficient natural regeneration has, however, been a concern for over a century. The objective of this study was to gain insights into differences in regeneration success using artificial and natural regeneration techniques for reforestation of oak (Quercus robur L.) stands. We monitored seedlings following planting, direct seeding and natural regeneration over five years in a randomized block experiment in southern Sweden with fenced and non-fenced plots. Fencing had a strong positive effect on height growth, especially for planted seedlings that were taller than the other seedlings and more frequently browsed in non-fenced plots. In contrast, there was little effect of fencing on survival, establishment rate and recruitment rate of seedlings. Due to aboveground damage on seedlings from voles, protection of acorns did not improve establishment rate following direct seeding. Under current circumstances at the site with a sparse shelterwood of old oaks, we conclude that natural regeneration was the most cost-efficient regeneration method. It resulted in the most seedlings at the lowest cost. However, regeneration success was heavily influenced by interference from herbaceous vegetation. With a small additional investment in vegetation control, the results might have been improved for planting and direct seeding.

Failed oak regeneration is widely reported in temperate forests and has been linked in part to changed disturbance regimes and land‐use. We investigated if the North American fire–oak hypothesis could be applicable to temperate European oaks (Quercus robur, Quercus petraea) using a replicated field experiment with contrasting canopy openness, protection against ungulate browsing (fencing/no fencing), and low‐intensity surface fire (burn/no burn). Survival, relative height growth (RGRH), browsing damage on naturally regenerated oaks (≤300 cm tall), and changes in competing woody vegetation were monitored over three years. Greater light availability in canopy gaps increased oak RGRH (p = .034) and tended to increase survival (p = .092). There was also a trend that protection from browsing positively affected RGRH (p = .058) and survival (p = .059). Burning reduced survival (p, We investigated if the North American fire–oak hypothesis could be applicable to temperate European oaks. Although a low‐intensity fire reduced oak seedling survival, survival rates were relatively high across treatment combinations (54%–92%) and relative height growth was greater in burned plots after 2 years. Burning did not change relative density of oaks, but it had a clear effect on competing woody vegetation as it reduced the number of individuals and their heights, especially for conifers.

Increasing species diversity is considered a promising strategy to mitigate the negative impacts of global change on forests. However, the interactions between regional climate conditions and species-mixing effects on climate-growth relationships and drought resistance remain poorly documented. In this study, we investigated the patterns of species-mixing effects over a large gradient of environmental conditions throughout Europe for European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.), two species with contrasted ecological traits. We hypothesized that across large geographical scales, the difference of climate-growth relationships and drought resistance between pure and mixed stands would be dependent on regional climate. We used tree ring chronologies derived from 1143 beech and 1164 pine trees sampled in 30 study sites, each composed of one mixed stand of beech and pine and of the two corresponding pure stands located in similar site conditions. For each site and stand, we used Bootstrapped Correlation Coefficients (BCCs) on standardized chronologies and growth reduction during drought years on raw chronologies to analyze the difference in climate-tree growth relationships and resistance to drought between pure and mixed stands.We found consistent large-scale spatial patterns of climate-growth relationships. Those patterns were similar for both species. With the exception of the driest climates where pure and mixed beech stands tended to display differences in growth correlation with the main climatic drivers, the mixing effects on the BCCs were highly variable, resulting in the lack of a coherent response to mixing. No consistent species-mixing effect on drought resistance was found within and across climate zones. On average, mixing had no significant effect on drought resistance for neither species, yet it increased pine resistance in sites with higher climatic water balance in autumn. Also, beech and pine most often differed in the timing of their drought response within similar sites, irrespective of the regional climate, which might increase the temporal stability of growth in mixed compared to pure stands. Our results showed that the impact of species mixing on tree response to climate did not strongly differ between groups of sites with distinct climate characteristics and climate-growth relationships, indicating the interacting influences of species identity, stand characteristics, drought events characteristics as well as local site conditions., The networking in this study has been supported by the COST Action FP1206 EUMIXFOR. All authors thank the numerous persons who contributed to the fieldwork in the different sites across Europe. We acknowledge the E-OBS dataset from the EU-FP6 project ENSEMBLES (http://ensembles-eu.metoffice.com) and the data providers in the ECA&D project (http://www.ecad.eu).

14 Pág., While the impacts of forest management options on carbon (C) storage are well documented, the way they affect C distribution among ecosystem components remains poorly investigated. Yet, partitioning of total forest C stocks, particularly between aboveground woody biomass and the soil, greatly impacts the stability of C stocks against disturbances in forest ecosystems. This study assessed the impact of species composition and stand density on C storage in aboveground woody biomass (stem + branches), coarse roots, and soil, and their partitioning in pure and mixed forests in Europe. We used 21 triplets (5 beech-oak, 8 pine-beech, 8 pine-oak mixed stands, and their respective monocultures at the same sites) in seven European countries. We computed biomass C stocks from total stand inventories and species-specific allometric equations, and soil organic C data down to 40 cm depth. On average, the broadleaved species stored more C in aboveground woody biomass than soil, while C storage in pine was equally distributed between both components. Stand density had a strong effect on C storage in tree woody biomass but not in the soil. After controlling for stand basal area, the mixed stands had, on average, similar total C stocks (in aboveground woody biomass + coarse roots + soil) to the most performing monocultures. Although species composition and stand density affect total C stocks and its partitioning between aboveground woody biomass and soil, a large part of variability in soil C storage was unrelated to stand characteristics., The European Union and the National Fund for Scientific Research (Fonds de la recherche scientifique) of Belgium supported this research as part the ERA-Net SUMFOREST project REFORM–Mixed species forest management. Lowering risk, increasing resilience (www.reform-mixing.eu). The lead author was further supported by Université catholique de Louvain for covid-19 related delays of his PhD project. Some of the triplets were selected, established and measured with funding from the EuMIXFOR FP1206 Cost Action project. The Polish State Forests Enterprise also supported one of the Polish co-authors (Grant No: OR.271.3.15.2017). The Orléans site, OPTMix was installed thanks to ONF (National Forest Service, France), belongs to research infrastructure ANAEE-F; it is also included in the SOERE TEMPO, ZAL (LTSER Zone Atelier Loire) and the GIS Coop network.

Arvicolinae rodents are known pests causing damage to both agricultural and forest crops. Today, rodenticides for rodent control are widely discouraged owing to their negative effects on the environment. Rodents are the main prey for several predators, and their complex olfactory system allows them to identify risks of predation. Therefore, the potential use of predators' scents as repellents has gained interest as an ecologically based rodent control method. In a two-choice experiment, we investigated the potential repellent effects of five synthetic predator compounds: 2-phenylethylamine (2-PEA), 2-propylthietane (2-PT), indole, heptanal and 2,5-dihydro-2,4,5-trimethylthiazoline (TMT), at 1% and 5% doses, using the bank vole (Myodes glareolus) as a rodent model.The compound 2-PEA reduced both the food contacts and the time spent by voles in the treatment arm compared to the control arm. Likewise, 2-PT-treated arms reduced the food contacts, and the voles spent less time there, although this latter difference was not significant. Indole also showed a tendency to reduce the time spent at the treatment arm; however, this result was not significant. Unexpectedly, TMT had the reverse effect in showing attractive properties, possibly due to odor cues from differently sized predators and intraguild predation in nature. We found no dose-related effects for any compounds tested.Our results suggest that the 2-PEA and 2-PT are both effective odor stimuli for triggering reduced food contacts and area avoidance, and they may be good repellent candidates. We suggest further testing of 2-PEA and 2-PT in field experiments to further determine their dose-efficiency as repellents against rodents in more natural environments. © 2022 The Authors. Pest Management Science published by John WileySons Ltd on behalf of Society of Chemical Industry.

Sprouting by woody plants can increase species resilience to disturbance and foster regeneration during periods with little recruitment from seed. Though sprouting often plays a critical role in oak forest regeneration, there is little information available on sprouting capacity and sprout physiology at the seedling stage, particularly for new germinants. This study compared sprouting capacity and sprout photosynthesis of shoot-clipped germinants of two temperate oaks established in contrasting light environments. We studied the North American Quercus alba and the European Q. robur, both are in the section Quercus and appear to share similar biological and ecological requirements. Sprouting capacity for both species was enhanced under high light availability (29% more sprouts per plant), a response not previously noted for oak germinants. Seedling sprouts acclimated to high light with a 34% decrease in leaf area ratio, a 56% increase in leaf mass per area, and a 49% increase in the light-saturated maximum photosynthetic rate. Though both species appeared similarly adapted to shoot loss, a greater sprouting capacity (29% more sprouts per plant) and plant-level net photosynthesis (73% higher) was observed for Q. robur, regardless of light environment. As naturally regenerated oak seedlings in forest understories often experience disturbance or stress resulting in shoot loss or die-back, our results highlight the importance of the light environment during early plant development. Our comparison of temperate oaks from different continents should facilitate exchange of successful stand regeneration practices within the range of temperate oak forests.

Forest cover is increasing in many regions due to spontaneous reforestation on abandoned pastures and fields. The resulting recent forests may need management to improve ecosystem quality, and this could possibly be combined with timber production in specific cases. Temperate deciduous (TD) trees have declined steeply during the past millennium, but some now increase in the recent forests, often mixed with Norway spruce. Removing spruce may benefit these trees and for example oak regeneration, flowering plants and pollination. The total area of forest suitable for restoration in Norway and Sweden is >100,000 ha. We evaluate the cost of selective cutting based on 26 field trials, 13 in each country, and sales from the initial cutting on average just barely compensate for the costs. By resurveying plots from a parallel project in Sweden, we found that about half of the cut volume had regrown after 16 years, and a second thinning may be needed in the near future. Coarse woody debris (CWD) had increased by 78%, indicating increasingly natural conditions. We conclude that selective cutting in recent forests may be part of a strategy to reach restoration and sustainability goals, but that long-term incentives for landowners need to be developed.

The scale of opportunity to implement forest restoration exceeds billions of ha worldwide, and a part of this area in northern temperate regions includes formerly oak ( Quercus spp.)-dominated ecosystems. The cost of achieving restoration is often high, and tends to increase with severity of ecosystem degradation. Therefore, it is important to develop cost-efficient regeneration practices to support forest restoration. Direct seeding of acorns, one of the earliest artificial forest regeneration techniques developed, offers several benefits including costs that can be about a third of planting oak seedlings. However, direct seeding is presently a more uncertain practice for establishing oak forests and woodlands than is planting seedlings. Much of this uncertainty can be a result of acorn depredation by rodents even though other factors may also limit oak establishment. This review provides a synthesis of foundational knowledge, particularly from Europe and North America, pertaining to the biology and ecology of acorn production, acorn germination, early seedling growth, and acorn depredation by granivorous rodents. We build on this knowledge to review research on operational direct seeding practices and four basic strategies for acorn depredation control (chemical, ecological, physical and silvicultural). We suggest that environmentally sound approaches to minimize acorn depredation and increase seedling establishment currently exists. For example, seeding operations probably hold higher chances for success if scheduled during years of high masting, if applied on open sites (areas with little shrub and tree cover), and if acorn lots are sized and sown at an appropriate depth. Several gaps in our knowledge limit the development of improved operational practices for broader success. We lack information on basic acorn biology and proper handling and storage practices for many of the oaks around the world. And, we need research to support development of new techniques or combinations of strategies and techniques that minimize acorn depredation under a wide range of site conditions. Nevertheless, our synthesis suggests that direct seeding will remain a cost-effective and environmentally sound practice for oak forest and woodland establishment, and it will likely gain expanded use as future research informs innovation that increases seed availability, decreases acorn depredation, and raises predictability of oak seedling establishment.

Wind is a natural disturbance factor in boreal and temperate forests having large ecological and economic consequences. We investigated recovery processes in forests severely damaged by windthrow, by conducting a systematic quantitative literature review of 34 case studies. We addressed three questions on forest ecosystem recovery: (1) Which forest regeneration processes dominate forest recovery after windthrow? (2) Which structures and processes enhance or impede forest recovery after windthrow? (3) Does salvage logging after windthrow influence forest recovery? Our analyses showed that the main focus of the reviewed studies was on post storm seedling regeneration and survival. Advanced regeneration from suppressed seedlings or saplings also played an important role in the studies, especially for shade tolerant species and in the boreal biome. Pits and mounds and coarse woody debris played an important role for the establishment of Picea sp., especially in the studies from the boreal biome, whereas in the temperate biome game interference and competition from ground vegetation seemed to be the most important influencing processes. Salvage logging mostly acted as a subsequent disturbance after the windthrow, pushing the forest ecosystem towards an earlier successional stage, hereby impeding recovery. In none of the studies however, did the windthrow nor the consequent salvaging halt recovery completely, confirming the resilience of forests as the dominant vegetation type in these biomes. Based on our results forest management implications are discussed.

Many tree species worldwide are suffering from slow or failed natural regeneration with dramatic consequences for biodiversity and ecosystem services. However, it is difficult to disentangle the complex effects of factors influencing regeneration processes on long-lived tree species at large scales. In this study, we use long-term data from the Swedish National Forest Inventory (1953–2015) combined with deer hunting data (1960–2015) to reveal experimentally-intractable processes impeding oak (Quercus spp.) regeneration in southern Sweden. Oak-dominated ecosystems are widespread in northern temperate regions, where oaks are foundation species with disproportionate importance for biodiversity and ecosystem functions. Our study reveals that during the last six decades, oak tree numbers and standing volume have continuously increased, while natural regeneration of oak declined steeply after the early 1980s. We connect this decline to denser and darker forests, combined with increased abundance of deer. Land use changes during the six decades, such as abandonment of traditional practices and large-scale introduction of forest management oriented towards high volume production, led to continuously denser forests and thereby reduced the oak regeneration niche. In addition, the impact of changed game management was evident. This was particularly clear from a natural experiment on Gotland, a large island free of deer until roe deer were introduced in the late 20th century, at which point oak regeneration began a steep decline. At the stand level, natural oak regeneration could be expected to mainly occur in pulses after disturbance events, followed by a period of low regeneration success as the cohort ages. However, at a landscape scale one would expect a mix of successional stages that would even out such demographic patterns. A prolonged period of low regeneration at a landscape scale will eventually lead to a large gap in the oak size distribution as was observed in this study. This could eventually hurt the many species dependent on old and large oak trees. Active management to restore the oak regeneration niche, i.e. forest habitats with more light and less browsing pressure, therefore seems essential. The latter includes developing strategies that manage both deer populations and their available food across landscapes. Our study is the first to link oak regeneration failure to long-term changes in land use and increased deer populations at a landscape scale in this region. Furthermore, our study show how historical data can clarify confounded processes impacting long-lived forest species.

Conventions and policies for biodiversity conservation and climate change mitigation state the need for increased protection, restoration and climate change adaptation of forests. Much degraded land may be targeted for large-scale forest restoration, yet challenges include costs, a shortage of regeneration material and the need for restored forests to serve as a resource for communities. To ensure ecosystem function for the future, forest restoration programs must: (1) learn from the past; (2) integrate ecological knowledge; (3) advance regeneration techniques and systems; (4) overcome biotic and abiotic disturbances and (5) adapt for future forest landscapes. Historical forest conditions, while site-specific, may help to identify the processes that leave long-term legacies in current forests and to understand tree migration biology/population dynamics and their relationship with climate change. Ecological theory around plant–plant interactions has shown the importance of negative (competition) and positive (facilitation) interactions for restoration, which will become more relevant with increasing drought due to climate change. Selective animal browsing influences plant–plant interactions and challenges restoration efforts to establish species-rich forests; an integrated approach is needed to simultaneously manage ungulate populations, landscape carrying capacity and browse-tolerant regeneration. A deeper understanding of limiting factors that affect plant establishment will facilitate nursery and site preparation systems to overcome inherent restoration challenges. Severe anthropogenic disturbances connected to global change have created unprecedented pressure on forests, necessitating novel ecological engineering, genetic conservation of tree species and landscape-level approaches that focus on creating functional ecosystems in a cost-effective manner.

We thank S. Tabik, E. Guirado, and Garnata Drone SL for fruitful debates about the application of remote sensing and artificial intelligence in restoration. E. McKeown looked over the English version of the manuscript. Original drawings were made by J. D. Guerrero. This work was supported by projects RESISTE (P18-RT-1927) from the Consejeria de Economia, Conocimiento, y Universidad from the Junta de Andalucia, and AVA201601.19 (NUTERA-DE I), DETECTOR (A-RNM-256-UGR18), and AVA2019.004 (NUTERA-DE II), cofinanced (80%) by the FEDER Program. F.M.-R. acknowledges the support of the Agreement 4580 between OTRI-UGR and the city council of La Zubia. We thank an anonymous reviewer for helpful comments that improved the manuscript., Forest restoration is currently a primary objective in environmental management policies at a global scale, to the extent that impressive initiatives and commitments have been launched to plant billions of trees. However, resources are limited and the success of any restoration effort should be maximized. Thus, restoration programs should seek to guarantee that what is planted today will become an adult tree in the future, a simple fact that, however, usually receives little attention. Here, we advocate for the need to focus restoration efforts on an individual plant level to increase establishment success while reducing negative side effects by using an approach that we term “precision forest restoration” (PFR). The objective of PFR will be to ensure that planted seedlings or sowed seeds will become adult trees with the appropriate landscape configuration to create functional and self-regulating forest ecosystems while reducing the negative impacts of traditional massive reforestation actions. PFR can take advantage of ecological knowledge together with technologies and methodologies from the landscape scale to the individual- plant scale, and from the more traditional, low-tech approaches to the latest high-tech ones. PFR may be more expensive at the level of individual plants, but will be more cost-effective in the long term if it allows for the creation of resilient forests able to providemultiple ecosystemservices. PFR was not feasible a few years ago due to the high cost and low precision of the available technologies, but it is currently an alternative that might reformulate a wide spectrum of ecosystem restoration activities., Junta de Andalucia P18-RT-1927, European Commission AVA201601.19 A-RNM-256-UGR18 AVA2019.004, OTRI-UGR 4580, city council of La Zubia 4580

15 Pág. Ecological Modelling, Tree species mixing of oak (Quercus petraea (Matt.) Liebl./Quercus robur L.) and pine (Pinus sylvestris L.) has been shown to have positive effects on ecosystem service provision. From a management perspective, however, it is still uncertain which thinning regime provides the highest possible productivity of mixed oak–pine forests in the long term. Because of a lack of empirical studies dealing with thinning and species mixing effects on oak–pine forests, we simulated forest growth in order to test which thinning type and intensity may provide the highest productivity in the long-term. To achieve this, we simulated the growth of pure and mixed stands of oak and pine for 100 years in 23 triplets located on an ecological gradient across Europe. For this purpose, we applied four different growth simulators and compared their results: the distance-independent single-tree simulator PROGNAUS, the distance-dependent single-tree simulator SILVA, the gap model ForCEEPS, and the process-based simulator 3D-CMCC-FEM. We investigated the effects of species mixing and thinning from the upper (thinning from above) and lower tail (thinning from below) of the diameter distribution by reducing the stand basal area to 50 and 80% of the maximum basal area. We compared simulated results of the relative volume productivity of mixed versus pure stands and of thinned versus unthinned stands to empirical results previously obtained on the same set of triplets. Simulated relative volume productivity ranged between 61 and 156%, although extremes of 10% and of 300% could be observed. We found the relative volume productivity to be influenced by stand age, but not by stand density, except for PROGNAUS. Relative volume productivity did not increase with the site water supply of the triplet location. Highest long-term productivity for oak, pine and oak–pine stands can be expected in consequence of thinning from above, but the effect of thinning intensity differed between simulators. Thinning effects were positively affected by stand density, but not by stand age, except for thinning from above predicted by PROGNAUS. Predicted thinning effects showed good approximation of results from thinning experiments for oak, but not for pine stands. We hypothesize the results might be caused by the insufficient simulator representation of climate and its interaction with other site variables and stand structure. Further work is needed to reduce the revealed limitations of the existing growth models, as we currently see no alternative to such kind of studies and simulators., The authors thank the European Union for funding the project “Mixed species forest management. Lowering risk, increasing resilience (REFORM)” under the framework of Sumforest ERA-NET. The authors from Austria also thank the Austrian Federal Ministry for Sustainability and Tourism for supporting the establishment of the Austrian triplet plots and for covering the work expenses of Markus Engel within the project ”Forstwirtschaft mit Mischwäldern – geringes Risiko, hohe Widerstandskraft – REFORM” under the grant number 101199. All contributors thank their national funding institutions to establish, measure and analyze data from the triplets. Maude Toïgo and Xavier Morin thank François de Coligny and Nicolas Beudez for their help in the development of the ForCEEPS model. Antonio Tomao, Carlo Trotta and Anna Barbati thank Alessio Collalti for his support and suggestions about the simulations with the 3D-CMCC-FEM model.

Mixed forests are suggested as a strategic adaptation of forest management to climate change. Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) are tree species of high economic and ecological value for European forestry. Both species coexist naturally in a large part of their distributions but there is a lack of knowledge on the ecological functioning of mixtures of these species and how to manage such stands. This paper analyses these species’ intra- and inter-specific competition, including size-symmetric vs. size-asymmetric competition, and explore the effect of weather conditions on tree growth and competition. We studied basal area growth at tree level for Scots pine and Norway spruce in mixed versus pure stands in 22 triplets of fully-stocked plots along a broad range of ecological conditions across Europe. Stand inventory and increment cores provided insights into how species mixing modifies tree growth compared with neighbouring pure stands. Five different competition indices, weather variables and their interactions were included and checked in basal area growth models using a linear mixed model approach. Interspecific size-asymmetric competition strongly influenced growth for both tree species, and was modulated by weather conditions. However, species height stratification in mixed stands resulted in a greater tree basal area growth of Scots pine (10.5 cm2 year−1) than in pure stands (9.3 cm2 year−1), as this species occupies the upper canopy layer. Scots pine growth depended on temperature and drought, whereas Norway spruce growth was influenced only by drought. Interspecific site-asymmetric competition increased in cold winters for Scots pine, and decreased after a drought year for Norway spruce. Although mixtures of these species may reduce tree size for Norway spruce, our results suggest that this could be offset by faster growth in Scots pine. How inter-specific competition and weather conditions alter tree growth may have strong implications for the management of Scots pine-Norway spruce mixtures along the rotation period into the ongoing climate change scenario.

Centro de Investigación Forestal (CIFOR), Mixed-species stands have been found to be more productive than would be expected from the performance of their component species in monocultures due to facilitation and complementarity between species, although these interactions depend on the combination of species present. Our study focuses on monospecific and mixed-species stands of Scots pine and Norway spruce using 20 triplets established in nine countries along a climatic gradient across Europe. Differences in mean tree and stand characteristics, productivity and stand structure were assessed. Basal area increment in mixed stands was 8% higher than expected while volume increment was only 2% greater. Scots pine trees growing in mixed-species stands showed 11% larger quadratic mean diameter, 7% larger dominant diameter, 17% higher basal area and 25% higher stand volume than trees growing in monospecific stands. Norway spruce showed only a non-significant tendency to lower mean values of diameters, heights, basal area, as well standing volume in mixtures than monocultures. Stand structure indices differed between mixed stands and monocultures of Scots pine showing a greater stratification in mixed-species stands. Furthermore, the studied morphological traits showed little variability for trees growing in monospecific stands, except for diameter at breast height, crown length and crown length ratio. For trees growing in mixed stands, all the morphological traits of the trees were identified as different. Some of these morphological traits were associated with relative productivity. Nevertheless, relative productivity in mixed-species stands was not related to site conditions., We thank national funders of REFORM project (Spanish Ministry of Science and Innovation: PCIN2017-026; Research Council of Lithuania: S-SUMFOREST-17-1) and those funders for the support to non-participants in the REFORM project (Denmark: Contract between Danish Ministry of Environment and Food and Department of Geosciences and Natural Resource Management of UCPH; Estonia: Estonian University of Life Sciences projects number P180024MIME and P200029MIME; Poland: EU CARE4C project (GA 778322) supported by the Polish Government MNiSW2018-2021 matching fund (W117/H2020/2018); Slovakia: APVV-15-0265) that allowed the establishment and measurement of the triplets. A grant for a research stay was received by RR-P from the CARE4C project (Carbon smart forestry under climate change, H2020-MSCA-RISE-2017)., 13 Pág.

Seed consumption by rodents causes substantial economic losses in agriculture and forest restoration. Rodents rely on their sensitive sense of smell to gather information about their environment. However, comparably little is known about how rodents use olfaction to locate food. We used bank voles to measure attraction to acorn odors in a Y-maze. Preferences were measured using two behaviors: approaching (time spent in odor preference zones) and investigation (numbers of nose pokes in odor nozzle), which yielded similar results. Shorter time intervals (15 and 30 s) in the preference zones were at least as good as the longer time interval (60 s) for detecting differences in approaching behavior. In this way, it is possible to reduce the measurement time with approximately 50%. Investigation, which was evaluated using only one time interval (180 s), yielded longer measurement time. Acorns were as preferred as the familiar, standard food (rodent chow) while an acorn aeration extract did not produce any response. We conclude that short measurement times for the evaluation of attractive odors makes it possible to efficiently assay the wide range of volatile compounds from bank voles’ natural foods which may be important in studies wishing to develop new rodent control methods.

Establishing mixed-species stands is frequently proposed as a strategy to adapt forests to the increasing risk of water scarcity, yet contrasted results have been reported regarding mixing effects on tree drought exposure. To investigate the drivers behind the spatial and temporal variation in water-related mixing effects, we analysed the δ13C variation in 22-year tree ring chronologies for beech and pine trees sampled from 17 pure and mixed pine–beech stands across a large gradient of environmental conditions throughout Europe. In the pure stands, average δ13C values were lower for beech (−27.9‰ to −22.2‰) than for pine (−26.0‰ to −21.1‰), irrespective of site conditions. Decreasing SPEI values (calculated over June to September) were associated with an increase in δ13C for both species, but their effect was influenced by stand basal area for pine and site water availability for beech. Mixing did not change the temporal constancy of δ13C nor the tree reaction to a drought event, for any of the species. While the mixing effect (Δ δ13C = δ13C pure stands − δ13C mixed stands) was on average positive for beech and non-significant for pine across the whole gradient, this effect strongly differed between sites. For both species, mixing was not significant at extremely dry sites and positive at dry sites; on moderately wet sites, mixing was positive for beech and negative for pine; at sites with permanent water supply, no general patterns emerge for any of the species. The pattern of mixing effect along the gradient of water availability was not linear but showed threshold points, highlighting the need to investigate such relation for other combinations of tree species., The networking in this study has been supported by COST Action FP1206 EUMIXFOR.

International audience; Just as the aboveground tree organs represent the interface between trees and the atmosphere, roots act as the interface between trees and the soil. In this function, roots take-up water and nutrients, facilitate interactions with soil microflora, anchor trees, and also contribute to the gross primary production of forests. However, in comparison to aboveground plant organs, the biomass of roots is much more difficult to study. In this study, we analyzed 19 European datasets on above- and belowground biomass of juvenile trees of 14 species to identify generalizable estimators of root biomass based on tree sapling dimensions (e.g. height, diameter, aboveground biomass). Such estimations are essential growth and sequestration modelling. In addition, the intention was to study the effect of sapling dimension and light availability on biomass allocation to roots. All aboveground variables were significant predictors for root biomass. But, among aboveground predictors of root biomass plant height performed poorest. When comparing conifer and broadleaf species, the latter tended to have a higher root biomass at a given dimension. Also, with increasing size, the share of belowground biomass tended to increase for the sapling dimensions considered. In most species, there was a trend of increasing relative belowground biomass with increasing light availability. Finally, the height to diameter ratio (H/D) was negatively correlated to relative belowground biomass. This indicates that trees with a high H/D are not only more unstable owing to the unfavorable bending stress resistance, but also because they are comparatively less well anchored in the ground. Thus, single tree stability may be improved through increasing light availability to increase the share of belowground biomass.

There is increasing empirical support for the biodiversity and ecosystem service (ES) benefits of mixed-species production forests. However, few studies control for the spatial arrangement of the trees within mixtures to determine the influence that clustering the tree species (patch scale mixtures), versus evenly dispersing them (intimate scale mixtures), may have for biodiversity and ES outcomes. To highlight the potential implications of altering tree spatial arrangement in mixtures, and the need to fill related knowledge gaps, here we provide a qualitative multi-disciplinary overview of ecological and socio-economic drivers with the potential to alter biodiversity, ecosystem services, and management-related outcomes from patch versus intimate scale mixtures. We focused our overview on even-aged mixtures of Norway spruce (Picea abies) and birch (Betula pendula or B. pubescens) in Sweden, which enabled us to contrast findings within a biogeographical and silvicultural setting. Specifically, we targeted implications for biodiversity (understory vascular plants, epiphytic lichens, saproxylic beetles, birds), biomass production, harvesting costs, management ease, recreation and aesthetics, cervid game, as well as abiotic and biotic risks (wind, fire, pathogens, pests, browsing damage). In the absence of direct empirical evidence, we primarily relied on expert inference from theory and relevant empirical studies sourced from the Fennoscandian region, and further afield if needed. Collectively these efforts allowed us to develop a number of informed hypotheses indicating that for spruce-birch mixtures in this region, patch scale mixtures may have the potential to favour the diversity of several forest dependent taxonomic groups, cervid game and reduce harvesting costs, whereas intimate mixtures may have the potential to reduce pathogen and pest damage, and likewise, potentially benefit production outcomes. Current knowledge was too limited, inconsistent or context dependent to even tentatively infer outcomes for fire risk, wind damage, browsing damage, management ease, recreational and aesthetic outcomes. We emphasize that our hypotheses require testing, but are sufficient to i) highlight the likely importance of spatial-scale to biodiversity and ecosystem services outcomes in mixed-species production forests, ii) caution against generalization from mixture studies that lack scale considerations, and iii) motivate the targeted consideration of spatial grain in future mixture studies.

Consumption and removal of buried seeds by granivorous rodents is one of the major problems when direct seeding is applied for restoration of oak (Quercus robur) and European beech (Fagus sylvatica) forests. In this laboratory study, the use of four seed treatments to potentially reduce bank vole (Myodes glareolus) consumption of beech nuts and acorns and a control was evaluated using a no-choice feeding set-up. The five seed treatments were: Chili (Capsicum chinense)/coconut fat, citronella (Cymbopogon winterianus)/rapeseed oils, mink (Mustela vision) excrement, sand coating as a physical barrier and a control. Seed germination tests were carried out with all the treatments. A total of 40 bank voles were individually given access to beech nuts or acorns at a rate of one treatment per day during two sessions. Mink excrement and chili/coconut fat treatments greatly reduced the consumption of beech nuts, and also reduced touching of beech nuts and acorns. In contrast, the sand coating treatment increased the consumption of both types of seeds. Germination of both beech nuts and acorns was reduced by the chilli/coconut fat and citronella/rapeseed oils treatments. Our results suggest that mink excrement has a potential as an effective repellent against bank voles when direct seeding is applied. However, further studies to determine the best method of application, as well as the efficiency under field conditions, are needed before definitive recommendations can be given to restoration managers.

This study applied a structured expert elicitation technique, the Delphi method, to identify the impacts of five forest management alternatives and several forest characteristics on the preservation of biodiversity and habitats in the boreal zone of the Nordic countries. The panel of experts consisted of a number of scientists in the field. The data was collected using a semi-structured questionnaire distributed via e-mail in two rounds. Our findings demonstrated that an increase in management intensity for timber production is likely to have a negative effect on the biodiversity and habitats with intense management alternatives such as a “clear-cutting system” resulting in the strongest adverse impact. The presence of deadwood, mixture of trees of different sizes and increase in stand age were expected to promote preservation of biodiversity and habitats. However, there was little agreement between experts regarding the functional form that relationships between preservation of biodiversity and forest characteristics take. The Delphi method was found useful in investigating the existing knowledge base and capable of contributing to a more comprehensive assessment for decision support as a valuable addition to on-going empirical and modeling efforts. The findings could assist forest managers in developing forest management strategies that generate benefits from timber production while taking into account the trade-offs with biodiversity goals.

1. When tree‐species mixtures are more productive than monocultures, higher light absorption is often suggested as a cause. However, few studies have quantified this effect and even fewer have examined which light‐related interactions are most important, such as the effects of species interactions on tree allometric relationships and crown architecture, differences in vertical or horizontal canopy structure, phenology of deciduous species or the mixing effects on tree size and stand density. 2. In this study, measurements of tree sizes and stand structures were combined with a detailed tree‐level light model (Maestra) to examine the contribution of each light‐related interaction on tree‐ and stand‐level light absorption at 21 sites, each of which contained a triplet of plots including a mixture and monocultures of Fagus sylvatica and Pinus sylvestris (63 plots). These sites were distributed across the current distribution of these species within Europe. 3. Averaged across all sites, the light absorption of mixtures was 14% higher than the mean of the monocultures. At the whole community level, this positive effect of mixing on light absorption increased as canopy volume or site productivity increased, but was unrelated to climate. At the species population or individual tree levels, the mixing effect on light absorption resulted from light‐related interactions involving vertical canopy structure, stand density, the presence of a deciduous species (F. sylvatica), as well as the effects of mixing on tree size and allometric relationships between diameter and height, crown diameter and crown length. 4. The mixing effects on light absorption were only correlated with the mixing effects on growth for P. sylvestris, suggesting that the mixing effects on this species were driven by the light‐related interactions, whereas mixing effects on F. sylvatica or whole community growth were probably driven by non‐light‐related interactions. 5. Synthesis. The overall positive effect of mixing on light absorption was the result of a range of light‐related interactions. However, the relative importance of these interactions varied between sites and is likely to vary between other species combinations and as stands develop. Czech Republic Ministry of Education, Youth and Sports. Grant Number: COST CZ ‐ LD14063 and and LD14074; COST (European Cooperation in Science and Technology). Grant Number: COST Action EuMIXFOR; German Research Foundation. Grant Number: FO 791/4‐1

We are grateful to the participants of the PEN-CAFoRR COST action, who have so far warmly welcomed this experiment by signing up to establishing local sites, and we look forward to ful filling this collaboration. We thank A. Palma, J. Oliet and T. Mora´n for suggestions on improv ing this protocol., The choice of revegetating via direct seeding or planting nursery-grown seedlings influences the potential stresses suffered by seedlings such as herbivory and drought. The outcome of the balance between both revegetation methods may ultimately depend on how species identity and traits such as seed and seedling size interact with environmental conditions. To test this, we will conduct a continental-scale experiment consisting of one mini-experiment replicated by multiple participants across Europe. Each participant will establish a site with seeded and planted individuals of one or more native, locally growing oak (Quercus) species; the selection of this genus aims to favour continental-scale participation and to allow testing the response of a widely distributed genus of broad ecological and economic relevance. At each site, participants will follow the present protocol for seed collection, seeding in the field, nursery cultivation, outplanting, protection against herbivores, site maintenance, and measurement of seedling performance and environmental variables. Each measurement on each species at each site will produce one effect size; the data will be analysed through mixed-effects meta-analysis. With this approach we will assess the main effect of revegetation method, species, plant functional traits, and the potential effect of site-specific effect moderators. Overall, we will provide a continental-scale estimate on the seeding vs. planting dilemma and analyse to what extent the differences in environmental conditions across sites, seed size, functional traits, and the phylogenetic relatedness of species can account for the differences in the effect of revegetation method on seedling performance across study sites and species., This collaborative experiment lacks specific funding and was designed to be as small, low-cost, and easy-to-implement as possible for each participant. The resources necessary to establish and monitor each experimental site as described in this document will be made available by each participant. Funding for the coordination of this experiment is available from grant RTI2018- 096187-J-100 from FEDER/ Spanish Ministry of Science, Innovation and Universities. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

orests represent the largest terrestrial ecosystems. They provide a multitude of ecosystem services that contribute to human well-being, from the production of wood for fuel or industry, to the provision of food, habitats for biodiversity and public amenities. However, perhaps even more important nowadays is their capacity to capture a consider-able amount of carbon through the growth of trees, associated vegeta-tion, and sequestrate it in the long term in forest soils or wood products. This is a major contribution to the mitigation of ongoing climate change, which threatens the integrity of natural ecosystems and more generally life on the planet. However, forest ecosystems are themselves subject to an accelerated increase in damage caused by climatic hazards. The trend towards increasing temperatures and drought, but also extreme events such as heat waves, increase the risk of windstorms and forest fires and trigger the development of outbreaks of insect pests, which lead to large scale tree mortality.

Poplars (Populus spp.) are among the fastest growing trees raised in temperate regions of the world. Testing of newly developed cultivars informs assessment of potential planting stock for local environments. Initial rooting by nine poplar clones was tested in moist and saturated soil conditions during an 18-day greenhouse experiment. Clones responded differently to soil moisture, particularly in number of roots, root distribution, and root dry mass accumulation. About 73% of cuttings planted in moist soil produced roots from callus tissue, whereas only 1% of cuttings planted in saturated soil developed such roots. This drove root distribution towards the basal section of cuttings in moist soil, while in saturated soil roots were more evenly distributed among all three below-ground sections of cuttings. Roots originating from the basal section of cuttings planted in moist soil were longer than roots originating from apical and middle sections. Conversely, roots from the apical and middle sections ...

Facilitation by a neighboring woody understory has been suggested as a cost-effective and sustainable way to regenerate oaks. However, concerns about reduced plant growth and quality due to competing neighboring vegetation have hindered implementation. Here we studied competitive effects from herbaceous and woody vegetation on survival, growth, canopy development and stem quality in pedunculate oak ( Quercus robur ) in an open-field experiment in southern Sweden. Oaks were grown for eight years in four different competition treatments: no competing vegetation, with herbaceous vegetation (mainly grasses), with woody vegetation, and with both herbaceous and woody vegetation. During the first four years, competition had little effect on oak survival. However, after eight growing seasons, survival rates decreased to about 20% for oaks surrounded by woody vegetation, in contrast to oaks grown with only herbaceous vegetation that had a survival rate of near 100%. Competition from herbaceous and woody vegetation both reduced oak stem diameter and height growth, but they affected height growth differently. During the first growing seasons, oaks in the treatment with woody vegetation were able to keep up with the height growth of the surrounding vegetation. Thereafter, height growth stagnated, and after eight growing seasons heights of oaks in the treatment with woody competitors were only 30–39% that of oaks in the treatment without competing vegetation. In contrast, competition from herbaceous vegetation only restricted oak height development marginally. Interspecific competition not only restricted growth and survival but also shifted shoot architecture, resulting in a greater frequency of oaks with straight monopodial stems. Although competition from both herbaceous- and woody vegetation positively affected stem straightness, plots with woody vegetation had a greater proportion (0.42) of oaks with a single straight monopodial stem. Our results demonstrate that the facilitative competitive effects from herbaceous and woody vegetation could be used to control allocation patterns in young oaks, promoting development of tall straight monopodial stems. Considering the observed trade-off between high stem quality and survival, we recommend long-term assessment of this trade-off prior to application in practical forestry.

Revisión e identificación de oportunidades de investigación en modelización de la dinámica de masas mixtas, Aim of study: Modelling of forest growth and dynamics has focused mainly on pure stands. Mixed-forest management lacks systematic procedures to forecast the impact of silvicultural actions. The main objective of the present work is to review current knowledge and forest model developments that can be applied to mixed forests. Material and methods: Primary research literature was reviewed to determine the state of the art for modelling tree species mixtures, focusing mainly on temperate forests. Main results: The essential principles for predicting stand growth in mixed forests were identified. Forest model applicability in mixtures was analysed. Input data, main model components, output and viewers were presented. Finally, model evaluation procedures and some of the main model platforms were described. Research highlights: Responses to environmental changes and management activities in mixed forests can differ from pure stands. For greater insight into mixed-forest dynamics and ecology, forest scientists and practitioners need new theoretical frameworks, different approaches and innovative solutions for sustainable forest management in the context of environmental and social changes., COST Action FP1206 EuMIXFOR (COST Association, European Comission), APVV-0480-12 and APVV-15-0265 (Slovak Research and Development Agency) and AGL-2014-51964-C2-1-R (Spanish Ministry of Economy and Competitiveness).

Past failures of monocultures, caused by wind-throw or insect damages, and ongoing climate change currently strongly stimulate research into mixed-species stands. So far, the focus has mainly been on combinations of species with obvious complementary functional traits. However, for any generalization, a broad overview of the mixing reactions of functionally different tree species in different mixing proportions, patterns and under different site conditions is needed, including assemblages of species with rather similar demands on resources such as light. Here, we studied the growth of Scots pine and oak in mixed versus monospecific stands on 36 triplets located along a productivity gradient across Europe, reaching from Sweden to Spain and from France to Georgia. The set-up represents a wide variation in precipitation (456–1250 mm year−1), mean annual temperature (6.7–11.5 °C) and drought index by de Martonne (21–63 mm °C−1). Stand inventories and increment cores of trees stemming from 40- to 132-year-old, fully stocked stands on 0.04–0.94-ha-sized plots provided insight into how species mixing modifies stand growth and structure compared with neighbouring monospecific stands. On average, the standing stem volume was 436 and 360 m3 ha−1 in the monocultures of Scots pine and oak, respectively, and 418 m3 ha−1 in the mixed stands. The corresponding periodical annual volume increment amounted to 10.5 and 9.1 m3 ha−1 year−1 in the monocultures and 10.5 m3 ha−1 year−1 in the mixed stands. Scots pine showed a 10% larger quadratic mean diameter (p p p p p p p

The recruitment of forest trees is driven by both bottom-up processes (the acquisition of resources) and top-down processes (herbivory). To initiate stand regeneration, foresters commonly reduce tree density to increase light levels for seedlings and enhance primary productivity. These changes in vegetation dynamics, however, could also influence effects of ungulate browsing, resulting in unintended consequences for forest management. Here, we assessed how effects of ungulate exclusion and canopy opening interacted to affect the regeneration of two oak species: Quercus robur and Quercus petraea. We monitored the growth and survival of oak seedlings for two to three growth seasons in paired fenced and unfenced plots under contrasting conditions of canopy openness (8% to 52%) at five sites in southern Sweden and three sites in northeastern France. We scored browsing in the unfenced plots by the four cervids occurring in these areas (Alces alces, Capreolus capreolus, Cervus elaphus and Dama dama). Fencing increased the growth of (mostly taller) seedlings occurring in Sweden and the survival of (mostly smaller) seedlings in France. Both effects increased as canopies became more open. Browsing reduced oak seedling growth in both countries, independently of canopy openness. Canopy openness increased browsing levels in Sweden. Cervid densities did not appear to modify how fencing affected oak seedling growth and survival. In both contrasting forest environments, creating gaps tended to enhance ungulate damage on young forest stands as browsing frequency increased. We conclude that net forest regeneration reflects a subtle equilibrium between enhancing resource availability, boosting seedling growth, and limiting herbivory, which curtails seedling growth and survival.

13 Pág. Instituto de Ciencias Forestales (ICIFOR), Mixed forests are usually associated with higher aboveground carbon storage compared to the corresponding monocultures but information on the impact of tree species mixing on soil organic carbon (SOC) is still limited. Yet, maximizing SOC storage is crucial for ecosystem C sequestration and many other ecosystem services. This study used a triplet approach (ie. two-species mixed stand and respective pure stands at the same site) to assess the impact of tree species identity and mixing on SOC storage in eight pine-oak, eight pine-beech and five beech-oak triplets in Europe. We sampled the forest floor (FF) and 0–40 cm in the mineral soil per 10 cm interval. For each triplet type, we fitted basal area (BA) proportion of one component species (for species identity) and a BA-based plot-level True Shannon Diversity index (for species mixing) as explanatory variables for SOC stocks in linear mixed effects models, which included stone content and plot BA as covariates, and site as a random intercept. Considering the total soil depth (FF + 0–40 cm), species identity effect on SOC stocks was only significant for pine-beech and pine-oak triplets but explained more variability in SOC stocks than species mixing across triplet types. Species mixing effect was not significant for any triplet type in the total soil depth. While species identity consistently drove SOC storage in the topsoil layers across triplet types, species mixing explained more variability in SOC stocks in the deeper soil layers except for pine-oak triplets. The results showed that species identity is a stronger driver of SOC storage than species mixing. While tree species identity effect was strongly related to a conifers vs broadleaves signature, the drivers behind mixing effects remained elusive. The results suggest that targeted selection of tree species could better enhance SOC storage in European forests than a mere increase in species richness., The European Union and the National Fund for Scientific Research (Fonds de la recherche scientifique) of Belgium supported this research as part the ERA-Net SUMFOREST project REFORM – Mixed species forest management. Lowering risk, increasing resilience (www.reform-mixing.eu). Some triplets were selected, established and measured with funding from the EuMIXFOR FP1206 Cost Action project. The Polish State Forests Enterprise also supported one of the Polish co-authors (Grant No: OR.271.3.15.2017). We are grateful to Karine Henin for her key role in the laboratory analyses of the samples. We appreciate the technical assistance by Benjamin Willems for soil sampling across Europe. We would like to thank Thomas Pérot for the dendrometric measurements in the Orléans sites. Finally, we are debtful to the two anonymous reviewers who contributed to improving a previous version of this manuscript.

Restoration of mixed oak forest in northern temperate regions is important for biodiversity and for adaptation of forest management to climate change. Direct seeding has been considered as a cost-effective method for the assisted regeneration of oaks. However, removal of acorns by granivorous rodents hinders its application. Patterns of acorn removal can vary with habitat type, presence of predators, and acorn size. In this field study, we tested the effects of distance to forest edge, predator excrement as a repellent, and acorn size on the performance of direct-seeded oak in southern Sweden. The experiment was carried out at two different sites. Our hypotheses were: (i) in clear-cuts, acorn removal is higher closer to the forest edge compared to open areas, (ii) treatment with predator excrement reduces acorn removal without affecting germination, and (iii) larger acorns will be removed more readily than smaller acorns. Finally, we also investigated if seedlings from larger acorns survive better and grow taller compared to smaller acorns in relation to habitat structure and predator excrement as repellent. Acorn removal differed at the two sites. At Skrylle (older clear-cut), no forest edge effects were found. At Klaverod (new clear-cut site), our results suggest that removal of acorns was higher in the open clear-cut due to the presence of large slash piles. Less vegetation coverage correlated with lower rates of acorn removal, except near slash piles. Our results therefore suggest that forest managers should reduce understory vegetation and avoid slash piles during direct seeding of oak. Mink excrement failed to protect acorns against removal, but did not reduce acorn germination. Bigger acorns produced taller seedlings but did not enhance overall woodland establishment due to their higher removal rate. Our results further suggest a potential food satiation effect due to an extra supply of additional food. Satiation manipulation might potentially be a method of mitigating the impact of seed predation by granivorous rodents during the direct seeding of oak, but such an approach requires further research before it could be recommended.

The oak-dominated woodlands and forests of northern Europe have experienced dramatic declines due to agriculture, urbanization, and conifer-dominated production forestry. These losses have had a substantial negative impact on biodiversity due to the large number of forest species which depend on oak and the environments oak-dominated forests provide. Production oak stands may serve as a means of supplementing or complementing the habitat provided by the limited remaining natural oak remnants in this region. Here we evaluate the extent to which oak plantations in temperate southern Sweden provide habitat and resources for bird communities, by surveying and contrasting the bird species composition and diversity found in mature and young production oak stands (5 and 8 replicates respectively) and protected oak-dominated remnant forests (5 replicates). The mature production stands possessed a bird community partially overlapping in bird species composition, and comparable in species richness (34 species) to that found within protected oak forests (39 species). Furthermore, the production oak forests surveyed hosted threatened or near threatened bird species, including black woodpecker (Dryocopus martius), goldcrest (Regulus regulus), starling (Sturnus vulgaris), and yellowhammer (Emberiza citrinella). Though production oak forests cannot replace the habitat provided by protected oak forests, these stands do appear to provide conditions consistent with the habitat and resource requirements of a diverse cross-section of bird species in this region, including species of substantial conservation concern. Production oak forests thus have the capacity to make a positive contribution to biodiversity conservation, as well as providing a diverse range of goods and services to society.