Aim Primary forests have high conservation value but are rare in Europe due to historic land use. Yet many primary forest patches remain unmapped, and it is unclear to what extent they are effectively protected. Our aim was to (1) compile the most comprehensive European‐scale map of currently known primary forests, (2) analyse the spatial determinants characterizing their location and (3) locate areas where so far unmapped primary forests likely occur. Location Europe. Methods We aggregated data from a literature review, online questionnaires and 32 datasets of primary forests. We used boosted regression trees to explore which biophysical, socio‐economic and forest‐related variables explain the current distribution of primary forests. Finally, we predicted and mapped the relative likelihood of primary forest occurrence at a 1‐km resolution across Europe. Results Data on primary forests were frequently incomplete or inconsistent among countries. Known primary forests covered 1.4 Mha in 32 countries (0.7% of Europe’s forest area). Most of these forests were protected (89%), but only 46% of them strictly. Primary forests mostly occurred in mountain and boreal areas and were unevenly distributed across countries, biogeographical regions and forest types. Unmapped primary forests likely occur in the least accessible and populated areas, where forests cover a greater share of land, but wood demand historically has been low. Main conclusions Despite their outstanding conservation value, primary forests are rare and their current distribution is the result of centuries of land use and forest management. The conservation outlook for primary forests is uncertain as many are not strictly protected and most are small and fragmented, making them prone to extinction debt and human disturbance. Predicting where unmapped primary forests likely occur could guide conservation efforts, especially in Eastern Europe where large areas of primary forest still exist but are being lost at an alarming pace.

Mixing of complementary tree species may increase stand productivity, mitigate the effects of drought and other risks, and pave the way to forest production systems which may be more resource-use efficient and stable in the face of climate change. However, systematic empirical studies on mixing effects are still missing for many commercially important and widespread species combinations. Here we studied the growth of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) in mixed versus pure stands on 32 triplets located along a productivity gradient through Europe, reaching from Sweden to Bulgaria and from Spain to the Ukraine. Stand inventory and taking increment cores on the mainly 60-80 year-old trees and 0.02-1.55 ha sized, fully stocked plots provided insight how species mixing modifies the structure, dynamics and productivity compared with neighbouring pure stands. In mixture standing volume (?12 %), stand density (?20 %), basal area growth (?12 %), and stand volume growth (?8 %) were higher Communicated by Peter Biber. than the weighted mean of the neighbouring pure stands. Scots pine and European beech contributed rather equally to the overyielding and overdensity. In mixed stands mean diameter (?20 %) and height (?6 %) of Scots pine was ahead, while both diameter and height growth of European beech were behind (-8 %). The overyielding and overdensity were independent of the site index, the stand growth and yield, and climatic variables despite the wide variation in precipitation (520-1175 mm year -1 ), mean annual temperature (6-10.5°C), and the drought index by de Martonne (28-61 mm°C -1 ) on the sites. Therefore, this species combination is potentially useful for increasing productivity across a wide range of site and climatic conditions. Given the significant overyielding of stand basal area growth but the absence of any relationship with site index and climatic variables, we hypothesize that the overyielding and overdensity results from several different types of interactions (light-, water-, and nutrient-related) that are all important in different circumstances. We discuss the relevance of the results for ecological theory and for the ongoing silvicultural transition from pure to mixed stands and their adaptation to climate change. Electronic supplementary material

Biomass and leaf area equations are often required to assess or model forest productivity, carbon stocks and other ecosystem services. These factors are influenced by climate, age and stand structural attributes including stand density and tree species diversity or species composition. However, such covariates are rarely included in biomass and leaf area equations. We reviewed the literature and built a database of biomass and leaf area equations for 24 European tree species and 3 introduced species. The final dataset contained 973 equations. Most of the equations were site-specific and therefore restricted to the edaphic, climatic and stand structural conditions of the given site. To overcome this limitation, the database was used to develop regional species-specific equations that can be used in a wide range of stands and to quantify the effects of climate, age and stand structure on biomass or leaf area. The analysis showed considerable inter-and intra-specific variability in biomass relationships. The intra-specific variability was related to climate, age or stand characteristics, while the inter-specific variability was correlated with traits such as wood density, specific leaf area and shade tolerance. The analysis also showed that foliage mass is more variable than stem or total aboveground biomass, both within and between species, and these biomass components have contrasting responses to age and changes in stand structure. Despite the large number of published equations, many species are still not well represented. Therefore, generic equations were developed that include species-specific wood density instead of species identity. Further improvements may be possible if future studies quantify the stand structure of individual tree neighbourhoods instead of using the stand means for all trees sampled with the given stand.

611. There is increasing evidence that species diversity enhances the temporal stability of 62 community productivity in different ecosystems, although its effect at population and tree 63 levels seems to be negative or neutral. Asynchrony between species was found to be one of 64 the main drivers of this stabilizing process. However, scarce research in this area has been 65 undertaken in forest communities, so determining the effect of species mixing on the stability 66 of forest productivity as well as the identity of the main drivers involved still poses a 67 challenging task. 3. Mixed stands showed a higher temporal stability of basal area growth than monospecific 76 stands at community level, but not at population or individual tree levels. Asynchrony 77 between species growth in mixtures was related to temporal stability, but neither overyielding 78 nor asynchrony between species growth in monospecific stands were linked to temporal 79 stability. Therefore, species interactions modify between-species asynchrony in mixed stands. 80Accordingly, temporal shifts in species interactions were related to asynchrony and to the 81 mixing effect on temporal stability. 4. Synthesis. Our findings confirm that species mixing can stabilize productivity at 83 community level whereas there is a neutral or negative effect on stability at population and 84 individual tree level. The contrasting findings as regards the relationships between temporal 85 stability and species asynchrony in mixed and monospecific stands suggest that the main 86 driver in the stabilizing process is the temporal niche complementarity between species rather 87 than differences in species specific responses to environmental conditions. 89 Keywords 91Temporal variability; mixed-species forests; plant-plant interactions; overyielding; 92 asynchrony; niche complementarity; organizational levels; 93 94