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Key message. Elevation markedly modified the species-specific phenotypic responses of trees to light. The effects from elevation mostly occurred at organ level (SLA) for the montane species, but at whole-plant level (allocation traits) for the subalpine ones. The subalpine species allocate more carbon to roots under closed canopies at low elevation. Contrary to expectations, most species displayed smaller specific leaf area at high elevation. The most drought-intolerant species was more severely affected by drought under shade than in open microsites. Context. Understanding the phenotypic responses of mountain tree species to different levels of local irradiance can be of critical importance for elucidating their capacity to relocate above their current distributional limit in response to environmental changes. Aims. To evaluate whether the response of different co-occurring forest tree species to local irradiance varies when they are growing at various elevations or beyond their current distributional limit. Methods. Seedlings of four tree species (Betula pendula Roth., Pinus sylvestris L., Abies alba Mill., and Pinus uncinata Ram. ex DC.) were planted under different irradiance levels (forest understory vs natural gaps) and at various elevation (montane–subalpine ecotone and subalpine belt). After four growing seasons, 48 plants per species were excavated to assess allocational (biomass distribution) and morphological (specific leaf area) traits. Midday leaf water potential was recorded during a period of intense drought. Results. The subalpine species (A. alba and P. uncinata) increased their allocation to the root system at low elevation and under dense canopy. We observed constant or higher SLA in all species when they develop in the subalpine belt. B. pendula was affected more severely by drought at low elevations and under shade than in open microsites. Conclusion. We found marked species-specific phenotypic variability of tree seedlings to increasing irradiance, with these responses modulated by the elevation at which the trees were growing. ; This study was funded by the Spanish Ministry of Economy and Competitiveness (MINECO) via the projects AGL2012-40039-C02-01 and AGL2015-70425-R. AA was supported by Spanish Government through the "Juan de la Cierva" fellowship program (IJCI-2016-30049). This research is a contribution to the CERCA Programme of the Generalitat de Catalunya.

Herbicide use in forestry is analysed from an historical and environmental perspective. First chemical herbicides were developed during the Second World War. Organochloride herbicides were widely used in the past but they are now classified as very harmful for human and the environment. However, recently developed herbicides like glyphosate present the same efficiency and a much lower toxicity. In general, the public opinion about herbicides is strongly negative. In Québec, all herbicides were banned from use in public forest after some environmental assessments. This decision seems to be more politically than scientifically based. In the case of intensive managed forest, mechanical treatments with forest tractors can present similar or even lower environmental impacts than glyphosate, but few studies exist to make an objective comparison. Furthermore, in terms of tree growth, low toxicity herbicides seem to present higher effectiveness than mechanical treatments. This possible growth gain can then be used to reduce pressure on natural forest by increasing protected areas and the use of ecosystem forest management. Nevertheless, the use of herbicides must be strictly monitored to reduce environmental risks. ; La problématique de l'utilisation des herbicides en foresterie est analysée selon une perspective historique et environnementale. Le développement des herbicides chimiques remonte à la fin de la deuxième guerre mondiale. Les premiers herbicides organochlorés étaient très efficaces, mais ils sont aussi très toxiques pour l'humain et l'environnement. Les herbicides développés plus récemment, comme le glyphosate, sont tout aussi efficace et beaucoup moins toxiques, mais ils sont mal perçus par la population. Au Québec, l'utilisation de tous les herbicides en forêt publique fut prohibée suite à une évaluation environnementale rigoureuse. Il semble que la décision d'abolir son utilisation était plus politique que scientifique. En effet, une comparaison sommaire des impacts environnementaux possibles du glyphosate comparativement aux dégagements mécaniques manuels et mécanisés ne permet pas de dégager lequel des traitements est préférable au niveau strictement environnemental. Puisque certains herbicides permettent une meilleure croissance des plantations, il est possible d'imaginer que ce gain de croissance pourrait être utilisé pour augmenter les aires protégées et le niveau d'aménagement écosystémique sur une proportion plus grande du territoire. Néanmoins l'utilisation d'herbicides devrait être largement surveillée tant au niveau de l'application qu'au niveau du suivi environnemental.

Aim To assess the spatial patterns of forest expansion (encroachment and densification) for mountain pine (Pinus uncinata Ram.) during the last 50 years at a whole mountain range scale by the study of different topographic and socio-economic potential drivers in the current context of global change. Location The study area includes the whole distributional area of mountain pine in the Catalan Pyrenees (north-east Spain). This represents more than 80 municipalities, covering a total area of 6018 km2. Methods Forest cover was obtained by image reclassification of more than 200 pairs of aerial photographs taken in 1956 and 2006. Encroachment and densification were determined according to changes in forest cover, and were expressed as binary variables on a 150 × 150 m cell-size grid. We then used logistic regression to analyse the effects of several topographic and socio-economic variables on forest expansion. Results In the period analysed, mountain pine increased its surface coverage by 8898 ha (an increase of more than 16%). Mean canopy cover rose from 31.0% in 1956 to 55.6% in 2006. Most of the expansion was found on north-facing slopes and at low altitudes. Socio-economic factors arose as major factors in mountain pine expansion, as encroachment rates were higher in municipalities with greater population losses or weaker primary sector development. Main conclusions The spatial patterns of mountain pine expansion showed a good match with the main patterns of land-use change in the Pyrenees, suggesting that land-use changes have played a more important role than climate in driving forest dynamics at a landscape scale over the period studied. Further studies on forest expansion at a regional scale should incorporate patterns of land-use changes to correctly interpret drivers of forest encroachment and densification. ; This research was primarily supported by the Spanish Ministry of Science and Innovation via the Consolider-Ingenio Montes project (CSD2008-00040) and the DINAMIX project (AGL2009-13270-C02). It was also supported by a Ramon y Cajal contract to L. Coll and L. Brotons, and a doctoral grant to the first author (AP2007-01663). Additional funding came from the Departament de Medi Ambient of the Regional Catalan Government. The authors thank the Department of Geography of the Universitat Autònoma de Barcelona for kindly providing access to aerial photographs, and Dr Gonzalez-Olabarria for valuable input on drafting the manuscript.

Questions How do thermal migration distance and extreme cold events affect seedling emergence and survival in assisted migration schemes in the sub-Mediterranean context? What role does plant provenance play? Can biotic interactions such as nurse effect of the overstorey and shrub layer buffer the negative responses to plant translocation? Are any of these effects species-specific? Location Three pinewoods in the Catalan Pre-Pyrenees, northeast Iberian Peninsula. Methods We used a replicated field trial to test the early years establishment of two contrasted provenances of four Quercus species (Q. coccifera, Q. ilex, Q. faginea and Q. pubescens) that were sown and planted along gradients of elevation and understorey microsite conditions in sub-Mediterranean pinewoods. Seedling responses to translocation were evaluated through seedling emergence, seedling survival and re-sprouting after dieback events according to seedling provenance, thermal migration distance, extreme cold events and microenvironment. Results The study reports high success of both the planting (with an overall 76.3% of initial 3-yr survival) and sowing (with an overall 50% of seedling emergence) experiments. The results show that: (1) the thermal migration distance and the occurrence of extreme cold events have strong effects on the responses of the translocated species (particularly the evergreen oaks); (2) the forest overstorey plays an important role in attenuating the negative effects of thermal migration distance on seedling survival; and (3) these responses are species-specific. The evergreen Quercus species showed more evidence of high ecotypic differentiation in terms of cold tolerance, enabling local provenances to respond better to translocation. In contrast, marcescent species, showed high phenotypic plasticity that led to a better overall establishment success. Conclusion The implementation of assisted migration is a feasible option to increase the diversity and resilience of the sub-Mediterranean pinewoods. Assisted migration programmes should manage risks by thoroughly considering thermal migration distances and the occurrence of extreme cold events when selecting species and seed sources, since Mediterranean tree species show different strategies regarding adaptation to cold. Programme managers should also consider the advantage of planting/sowing under relatively closed canopy to buffer some of the negative responses associated with translocation. ; This research was primarily supported by the European MED project 'ForClimadapt' (Adaptation of Mediterranean woodlands to climate change) and the Spanish Ministry of Science and Innovation via the RESILFOR project (AGL2012‐40039‐C02‐01). The Catalan Agency for Management of University and Research Grants provided S.M.A. with support through a 'pre‐doctoral' grant (FI‐DGR) and the Spanish Ministry of Science and Innovation provided L.C. with support through a post‐doctoral 'Ramon y Cajal' contract. This work benefited from a short‐term scientific exchange grant provided to S.M.A. by the Marie Curie IRSES project NEWFORESTS exchange programme (financed under EU FP7). The authors thank the Catalan Government, Catalunya Caixa's Social Work, Manuel Garrabou and the residents of Cabó valley for providing access to the sites in which the experiment was set up, and to Marc Cortina, Aida Sala, Roberto Solsona, Vicent Vidal and Sergio Martínez for invaluable help in setting up and monitoring the experiment.

The present study analyzes the effects of different socioeconomic factors on the frequency of fire ignition occurrence, according to different original causes. The data include a set of documented ignition points in the region of Catalonia for the period 1995–2008. The analysis focused on the spatial aggregation patterns of the ignitions for each specific ignition cause. The point‐based data on ignitions were interpolated into municipality‐level information using kernel methods as the basis for defining five ignition density levels. Afterwards, the combination of socioeconomic factors influencing the ignition density levels of the municipalities was analyzed for each documented cause of ignition using a principal component analysis. The obtained results confirmed the idea that both the spatial aggregation patterns of fire ignitions and the factors defining their occurrence were specific for each of the causes of ignition. Intentional fires and those of unknown origin were found to have similar spatial aggregation patterns, and the presence of high ignition density areas was related to high population and high unemployment rates. Additionally, it was found that fires originated from forest work, agricultural activities, pasture burning, and lightning had a very specific behavior on their own, differing from the similarities found on the spatial aggregation of ignitions originated from smokers, electric lines, machinery, campfires, and those of intentional or unknown origin. ; The present study was the result of a request from the Fire Prevention Service of the Catalan Government. The authors thank the Ramon y Cajal program from the Spanish Ministry of Science and Education for supporting the work of Dr. González‐Olabarria and Dr. Coll.

Ecological processes within forests provide vital ecosystem services to society, most of which depend on the persistence of tree cover that can be altered after the impact of a disturbance. The aim of the present study was to examine the role of seed dispersal and resprouting that mediate resilience to large fires and evaluate the economic costs that these ecological functions provide. We used field data from 412 plots of the Spanish National Forest Inventory providing information on pre- and post-fire conditions of Mediterranean Pinus spp. and Quercus spp.-dominated forests. Then, we determined the need for restoration (N Rest) and estimated the minimum pre-fire densities needed to ensure adequate post-fire cover. Economic valuations were assessed through three different scenarios (Sc) of possible human-management actions aimed at ensuring proper post-fire tree cover: Sc. 1) a pre-fire management scenario evaluating the costs of planting Quercus spp. seedlings in the understory, mimicking the whole dispersal function; Sc. 2) a pre-fire scenario in which enrichment plantations increased the densities of natural oaks; and Sc. 3) a post-fire scenario where the restoration is done through planting pines within the burned area. Approximately 90% of the burned area (371 out of 412 plots) was able to recover after fire supporting the view that Mediterranean forests are resilient to fire. This resilience was primarily mediated by biotic seed dispersal and posterior resprouting of tree species. These ecological functions saved between 626 and 1,326 €/ha compared to the human-management actions. Ensuring key ecological processes within forests increases forest resilience and recovery after fire leading to a generally significant saving of economic resources. In a perspective of increased future impact of disturbances and decrease availability of economic resources for forest management, the implications of the present study can be far reaching and extended to other forest planning exercises. ; This research was primarily supported by the Spanish Ministry of Science and Innovation via CGL2008-05506-C02-01/BOS project and the Consolider-Ingenio Montes project (CSD2008-00040); a Ramon y Cajal contract to LB and LC; and a Juan de la Cierva contract to JRG. CPP was partially supported by a Fundacion Caja Madrid grant. Partial funding was also provided by the Catalan Government grant SGR2009-531.

We investigate how the foliage mass to wood area ratios depend on tree and stand characteristics of previously collected data from Scots pine (Pinus sylvestris L.). Our analysis allowed a separation of the relationship between stem and branch cross-sectional areas and the relationship between the branch cross-sectional area and foliage mass. We studied how these relationships varied within and between stands. The lowest site fertility class had a higher foliage mass to stem area ratio than better sites. The relative height of a tree in the stand (Φ) was the major factor that determined the variation in the relationship between the branch cross-sectional area and the stem cross-sectional area. Models based on absolute height or tree diameter were usually weaker. Models based on Φ were simpler, since no other variables were able to explain between-stand variation in the presence of Φ. We were able to predict changes in the branchiness of the tree but not in the foliage mass supported per unit of branch area. ; Les auteurs examinent de quelle façon les rapports entre la biomasse foliaire et la surface de bois sont affectés par les caractéristiques des arbres et des peuplements à partir de données précédemment récoltées sur le pin sylvestre (Pinus sylvestrisL.). Leurs analyses ont permis de séparer la relation entre la surface radiale de la tige et desbranches de la relation entre la surface radiale des branches et la biomasse foliaire. Ils ont étudié de quelle façon ces relations varient à l'intérieur des peuplements et entre les peuplements. La plus faible classe de station était associée à un rapport de la biomasse foliaire sur la surface de la tige plus élevé que celui des stations plus riches. La hauteur relative d'un arbre dans le peuplement (Φ) constituait le principal facteur pour déterminer la variation de la relation entrela surface radiale des branches et celle de la tige. Les modèles basés sur la hauteur absolue ou sur le diamètre des arbres étaient généralement moins performants. Les modèles basés sur Φ étaient plus simples puisqu'une fois cette variable introduite dans le modèle, aucune autre variable ne pouvait expliquer la variation entre les peuplements. Ils ont pu prédire les changements dans la branchaison d'un arbre, mais pas dans la biomasse foliaire par unité de surface radiale des branches. ; Field data were collected with the support of the Academy of Finland, the Finnish Foundation for Research on Natural resources, the European Union (during the LTEEF project), and the Ministry of Agriculture and Forestry.

Evidence of tree regeneration failure of some species in the Iberian Peninsula forests warns us about the impact that the global change may exert on the preservation of Mediterranean forests, such as we know them. Predictions agree about an exacerbation of the summer drought there, acknowledged as the main limiting factor for the recruits' survival. On the other hand, many studies have also proved the relevant role that local heterogeneity has over the spatial distribution of forest species recruitment by providing safe sites. Therefore, to unravel how climate interacts with local factors over juveniles' performance seems crucial for the design of successful management strategies that allow facing the global warming. Here, we surveyed the natural recruitment of four dominant tree species in seven mountainous regions in the Iberian Peninsula, along entire elevational ranges as surrogates of their climatic ranges. Two of them have alpine and temperate distributions with populations at their rear edge in the Spanish mountains: Fagus sylvatica and Pinus uncinata; and the other two have a genuine Mediterranean distribution: Quercus ilex and Pinus nigra. Our main goal was to analyze for each species the effect of climate, local factors (i.e. light availability, stand structure and ground cover) and the interactions among them to identify the main drivers leading the regeneration process, assessed in terms of presence, abundance and mean annual growth of juveniles. The results showed different environmental factors determining the recruitment patterns of each species. Nevertheless, they highlighted the pervasive role exerted by both climate and fine scale factors, particularly the co-occurring vegetation on recruits' abundance, and the light availability on their growth. Moreover, we found some interactions among annual mean temperature and local factors, suggesting that climate and local heterogeneity act hierarchically, i.e. the local conditions may mitigate or exacerbate the impact of climate on juveniles. These results advocate for further research to increase our knowledge on the complex net of interactions among factors involved in recruitment at different scales, which in turn should be taken into account and incorporated in forthcoming management strategies. ; RB was funded by a Marie Curie IEF fellowship (FP7-PEOPLE-2011-IEF). Funding was also provided by the Spanish Ministry for Innovation and Science with the Grant Consolider-Montes (CSD2008_00040), and the European Union with the projects BACCARA (CE: FP7-226299, 7FP), FunDivEUROPE (CE: FP7-ENV-2010. 265171), and IMBALANCE-P (ERC Synergy project SyG-2013-610028).

The increase in frequency and intensity of droughts due to climate change might threaten forests under stress levels causing dieback and mortality episodes. Thus, deciphering how tree species from within a region respond to drought along environmental gradients should help us to understand forest vulnerability to climate change. To enlighten contrasting drought responses of dominant tree species, we reconstructed vegetation activity using Normalized Difference Vegetation Index (NDVI) and radial growth using tree-ring width series. We studied six tree species, three angiosperms (Fagus sylvatica, Quercus humilis, and Quercus ilex) and three gymnosperms (Pinus sylvestris, Pinus nigra, and Pinus halepensis), inhabiting a Mediterranean region in north-eastern Spain. We investigated if reduced growth resilience and increased growth synchrony after successive droughts (1986, 1989, 2005, and 2012): (i) were related to cumulative drought stress and (ii) preceded forest dieback in dry sites as compared to wet sites. In 2016, dieback affected Q. ilex and P. sylvestris stands in dry sites showing lower growth rates and NDVI. No dieback symptoms were observed in other species from dry (P. nigra, P. halepensis) or wet (F. sylvatica, Q. humilis, P. sylvestris) sites. Hot and dry summer conditions constrained growth and reduced NDVI. During 2005, a severe drought affected all species, but growth drops were more marked in dry places. All species were able to recover after extreme droughts, albeit angiosperms displayed lower than expected values of growth after the 2012 drought. Growth synchrony was higher in dry sites than in wet sites, and the differences were higher after the 2005 drought. This study reveals that the sensitivity of tree species to drought in species inhabiting the same region is species dependent, and it is contingent on local conditions with higher effects in dry sites than in wet sites. We describe how a cumulative impact of successive droughts increases growth synchrony and triggers the occurrence of dieback events in Mediterranean forests. ; JC, AG, and RS-S acknowledge the support of the FORMAL (RTI2018-096884-B-C31) and LESENS (RTI2018-096884-B-C33) projects from the Spanish Ministry of Science, Innovation and Universities; and VULBOS project (UPO-1263216) from the ERDF funds Andalusia regional government 2014-2020. GS-B was supported by Spanish Ministry of Economy, Industry and Competitiveness Postdoctoral grant (FJCI 2016-30121; FEDER funds) and from the European Union through the CANOPEE Interreg POCTEFA project.

Key message. No temporal change was recorded during summer in fuel availability in Pinus pinaster stands, contrary to predictions from the Forest Fire Weather Index. Also, thinning had no mid-term effect on fuel moisture or canopy structure. Context. Forest fires are a major problem in Mediterranean countries. Management actions, such as fuel reductions, are one of the main tools to diminish fire risk, but the midterm efficacy of such tools remains largely untested with empirical data. Aims. Here, we test for midterm effects of thinning on fuel moisture and crown bulk density in P. pinaster stands and whether temporal variations in fuel moisture correlated with predictions from the Fire Weather Index, a commonly used index on fire risk, and its components. Methods. We compared fuel moisture over a fire season and crown bulk density in nine pairs of thinned/unthinned plots 7 years after treatments were applied. Results. We observed that fuel moisture remained stable during a fire season, as a likely result of drought-induced physiological adjustments, including stomatal regulation and others, which allow leaves to maintain a large humidity even during drought, and that thinning had no midterm effect on fuel moisture or crown bulk density. Moreover, the Fire Weather Index and its components displayed different temporal dynamics than those observed in fuel moisture. Conclusion. These results are important as they indicate that thinning may only have a limited, short-term impact towards diminishing the potential for crown fire spread in these stands and that current indices to evaluate fire risk may require a re-evaluation. ; This study is funded by the Spanish Government (RYC-2012-10970, AGL2015-69151-R, AGL2015-68274-C3-3-R).

Science and society are increasingly interested in predicting the effects of global change and socio-economic development on natural systems, to ensure maintenance of both ecosystems and human well-being. The Intergovernmental Platform on Biodiversity and Ecosystem Services has identified the combination of ecological modelling and scenario forecasting as key to improving our understanding of those effects, by evaluating the relationships and feedbacks between direct and indirect drivers of change, biodiversity, and ecosystem services. Using as case study the forests of the Mediterranean basin (complex socio-ecological systems of high social and conservation value), we reviewed the literature to assess (1) what are the modelling approaches most commonly used to predict the condition and trends of biodiversity and ecosystem services under future scenarios of global change, (2) what are the drivers of change considered in future scenarios and at what scales, and (3) what are the nature and ecosystem service indicators most commonly evaluated. Our review shows that forecasting studies make relatively little use of modelling approaches accounting for actual ecological processes and feedbacks between different socio-ecological sectors; predictions are generally made on the basis of a single (mainly climate) or a few drivers of change. In general, there is a bias in the set of nature and ecosystem service indicators assessed. In particular, cultural services and human well-being are greatly underrepresented in the literature. We argue that these shortfalls hamper our capacity to make the best use of predictive tools to inform decision-making in the context of global change. ; This work was supported by the Spanish Government through the INMODES project (grant number CGL2017-89999-C2-2-R), the ERA-NET FORESTERRA project INFORMED (grant number 29183), and the project Boscos Sans per a una Societat Saludable funded by Obra Social la Caixa (https://obrasociallacaixa.org/). AMO and AA were supported by Spanish Government through the "Juan de la Cierva" fellowship program (IJCI-2016-30349 and IJCI-2016-30049, respectively). JVRD was supported by the Government of Asturias and the FP7-Marie Curie-COFUND program of the European Commission (Grant "Clarín" ACA17-02).

Climate change is expected to alter the geographic distribution of many plant species worldwide. However, there is still no clear evidence showing a generalised direction and magnitude of these distribution shifts. Here, we have surveyed, in nine mountainous regions in Spain, an array of tree species along entire elevational ranges, as surrogates of their global climatic ranges, to test for elevational shifts towards cooler locations. We analysed the distribution recruitment patterns of five dominant tree species, recording the abundance and measuring the primary growth of juveniles in 306 plots. Three of the species have a temperate-boreal distribution with populations at their southern edge in the Mediterranean mountain ranges: Pinus sylvestris, Pinus uncinata and Fagus sylvatica; and the other two species have a Mediterranean distribution: Quercus ilex and Pinus nigra. Despite the contrasting phylogenies and biogeographies, we identified a similar pattern in recruitment abundance across species, with an asymmetric distribution of juveniles (more recruits in the middle-upper elevation of their range), but higher annual growths at lower elevations. This survival-growth trade-off at the early recruitment stage may potentially counterbalance at population level the negative effect of global warming on recruit survival at the lower edge of species ranges. These findings suggest a demographic stabilisation process at the early recruitment stage of these tree species, and highlight the importance of considering the different demographic stages across the whole climatic range to understand the effects that climate change may exert on species distributions and population dynamics. ; RB was funded by a Marie Curie IEF fellowship (FP7-PEOPLE-2011-IEF). Funding also was provided by the Spanish Ministry for Innovation and Science with the grant Consolider-Montes (CSD2008_00040), VULGLO (CGL2010 22180 C03 03), MOUNTAINS (CGL-2012-38427), the Community of Madrid grant REMEDINAL 2 (CM S2009 AMB 1783) and the European Union with the projects BACCARA (CE: FP7-226299, 7FP) and FunDivEUROPE (CE: FP7-ENV-2010. 265171).

Tree species mixing has been widely promoted as a promising silvicultural tool for reducing drought stress. However, so far only a limited number of species combinations have been studied in detail, revealing inconsistent results. In this study, we analysed the effect of mixing Scots pine and oak (pedunculate oak and sessile oak) trees on their drought response along a comprehensive ecological gradient across Europe. The objective was to improve our knowledge of general drought response patterns of two fundamental European tree species in mixed versus monospecific stands. We focused on three null hypotheses: () tree drought response does not differ between Scots pine and oak, () tree drought response of Scots pine and oak is not affected by stand composition (mixture versus monoculture) and () tree drought response of Scots pine and oak in mixtures and monocultures is not modified by tree size or site conditions. To test the hypotheses, we analysed increment cores of Scots pine and oak, sampled in mixed and monospecific stands, covering a wide range of site conditions. We investigated resistance (the ability to maintain growth levels during drought), recovery (the ability to restore a level of growth after drought) and resilience (the capacity to recover to pre-drought growth levels), involving site-specific drought events that occurred between 1976 and 2015. In monocultures, oak showed a higher resistance and resilience than Scots pine, while recovery was lower. Scots pine in mixed stands exhibited a higher resistance, but also a lower recovery compared with Scots pine in monocultures. Mixing increased the resistance and resilience of oak. Ecological factors such as tree size, site water supply and site fertility were found to have significant effects on the drought response. In the case of Scots pine, resistance was increased by tree size, while recovery was lowered. Resistance of oak increased with site water supply. The observed mixing effect on the tree drought response of Scots pine and oak was in some cases modified by the site conditions studied. Positive mixing effects in terms of resistance and resilience of oak increased with site water supply, while the opposite was found regarding recovery. In contrast, site fertility lessened the positive mixing effect on the resistance of Scots pine. We hypothesise that the observed positive mixing effects under drought mainly result from water- and/or light-related species interactions that improve resource availability and uptake according to temporal and spatial variations in environmental conditions. ; This work was supported by the European Union as part of the ERA-Net SUMFOREST project REFORM – Mixed species forest management. Lowering risk, increasing resilience (2816ERA02S, PCIN2017-026) and the Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 778322. All contributors thank their national funding institutions for supporting the establishment, mensuration and analysis of the studied triplets. The first author wants to thank the German Federal Ministry of Food and Agriculture (BMEL) for financial support through the Federal Office for Agriculture and Food (BLE) (grant number 2816ERA02S), as well as the Bayerische Staatsforsten (BaySF) and Landesbetrieb Forst Brandenburg for providing suitable research sites. Research on the Lithuanian triplets (LT 1, LT 2) was made possible by the national funding institution Research Council of Lithuania (LMTLT) (agreement number S-SUMFOREST-17-1). The French site FR 1 belongs to the OPTMix experimental site (https://optmix.irstea.fr), which is supported annually by Ecofor, Allenvi, and the French national research infrastructure ANAEE-F. A special thank is due to Peter Biber for supporting the statistical analysis.