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International audience; Scale dependency is one of the main factors causing the variability of correlations among species diversity parameters. Recent syntheses demonstrated how both extent (the geographical area comprised by the survey or total sample) and grain (the scale of each sampling unit) have a significant effect on cross-taxon congruency. These results, however, do not represent a definitive framework to understand this variation across spatial scales, since this was only indirectly analyzed, by comparing the results of different studies. Our goal is to assess if and how cross-taxon congruency vary across different spatial scales in European temperate forests. Our general hypothesis is that cross-taxon congruency in species richness and composition in European temperate forests increases together with the scale of analysis. We account separately for differences in spatial grain and extent, and evaluate the relationships between all the possible pairs of taxonomic groups. We use a comprehensive set of field data encompassing Italy, France and Hungary (Fig. 1), and including species diversity information for six taxonomic groups: vascular plants, bryophytes, birds, epiphytic lichens, saproxylic beetles, and wood-inhabiting fungi. We calculated effect sizes for species richness and community composition correlation at three different spatial scales of grain and extent: (i) plot grain - site extent, (ii) plot grain - continental extent, and (iii) site grain - continental extent. No pair of taxa had their species richness consistently correlated (either positively or negatively) in all three combinations of grain and extent analyzed (Fig. 2). However, birds and bryophytes, and fungi and lichens had the highest correlation of species richness when sampled at a plot-level grain and site extent. When analyzing congruent patterns of species composition, plants resulted as the best surrogates for other taxa, even across different spatial scales (Fig. 3). We demonstrate that diversity congruency relationships among taxa in European temperate forest are for the most part, scale-dependent. Our results support that increasing database extent and sampling grain masks local patterns of congruency and highlights those due to common response to broad environmental and biogeographic factors that covary across the European continent. We suggest the results presented in this study to be taken into serious consideration when developing indicators of sustainable forest management for the conservation of forest biodiversity.

International audience; Managing forests sustainably is important to preserve biodiversity and the services it underpins, above all climate change mitigation through the storage of carbon in woody biomass. Biodiversity conservation and carbon storage strictly depend on forest structure, and many scientists advocate for a higher degree of structural complexity in order to increase the provision of these ecosystem services. However, a thorough understanding of the trade-offs and synergies between forest biodiversity, structure and function is still lacking especially due to the scattered and inadequate information on the distribution of forest biodiversity, whose sampling and monitoring are particularly complex and costly. By establishing a network of scientists who collected data in European deciduous forests, we were able to create a dataset including information on forest structure and six taxonomic groups (vascular plants, lichens, bryophytes, fungi, beetles and birds) for more than 350 sampling units across France, Hungary and Italy. We used these data to test the following hypotheses: i) a higher degree of forest structural heterogeneity results in higher levels of multi-taxon biodiversity; ii) forest stands containing a high amount of carbon stored in tree aboveground biomass re also those hosting a high degree of multi-taxon biodiversity.

International audience; Reviewing of research has an important place in scientific progress: it enables us to assess whether the results can be generalised or not. Reviews provide useful summaries of sometimes very complex and controversial subjects. In this communication, we explained what a formal meta-analysis is and how to proceed and then briefly summarised related methodological problems. Then, we gave one example of a published meta-analysis that tested the relationship between tree species diversity and forest insect herbivory. Finally, we presented the meta-analysis we performed within the Alter-net network on the differences of species richness between unmanaged and managed forests throughout Europe. More specifically, we wanted to analyse whether the response to forest management could differ among taxonomic groups and whether the variability of their response could depend on the time since forest abandonment and the type of forest management. Time schedule and main results were presented.