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Plant diversity is an important driver of diversity at other trophic levels, suggesting that cascading extinctions could reduce overall biodiversity. Most evidence for positive effects of plant diversity comes from grasslands. Despite the fact that forests are hotspots of biodiversity, the importance of tree diversity, in particular its relative importance compared to other management related factors, in affecting forest‐associated taxa is not well known. To address this, we used data from 183 plots, located in different forest types, from Mediterranean to Boreal, and established along a climatic gradient across six European countries (FunDivEUROPE project). We tested the influence of tree diversity, tree functional composition (i.e. functional trait values), forest structure, climate and soil on the diversity and abundance/activity of nine taxa (bats, birds, spiders, microorganisms, earthworms, ungulates, foliar fungal pathogens, defoliating insects and understorey plants) and on their overall diversity and abundance/activity (multidiversity,multiabundance/activity). Tree diversity was a key driver of taxon‐level and overall forest‐associated biodiversity, along with tree functional composition, forest structure, climate and soil. Both tree species richness and functional diversity (variation in functional trait values) were important. The effects of tree diversity on the abundance/activity of forest‐associated taxa were less consistent. Nonetheless, spiders, ungulates and foliar fungal pathogens were all more abundant/active in diverse forests. Tree functional composition and structure were also important drivers of abundance/activity: conifer stands had lower overall multidiversity (although the effect was driven by defoliating insects), while stands with potentially tall trees had lower overall multiabundance/activity. We found more synergies than trade‐offs between diversity and abundance/activity of different taxa, suggesting that forest management can promote high diversity across taxa. Our results clearly show the high value of mixed forest stands for multiple forest‐associated taxa and indicate that multiple dimensions of tree diversity (taxonomic and functional) are important.

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Fons van der Plas [et al.].- Received 8 September 2015, Accepted 19 February 2016, Published 24 March 2016, There is considerable evidence that biodiversity promotes multiple ecosystem functions (multifunctionality), thus ensuring the delivery of ecosystem services important for human well-being. However, the mechanisms underlying this relationship are poorly understood, especially in natural ecosystems. We develop a novel approach to partition biodiversity effects on multifunctionality into three mechanisms and apply this to European forest data. We show that throughout Europe, tree diversity is positively related with multifunctionality when moderate levels of functioning are required, but negatively when very high function levels are desired. For two well-known mechanisms, ‘complementarity’ and ‘selection’, we detect only minor effects on multifunctionality. Instead a third, so far overlooked mechanism, the ‘jack-of-all-trades’ effect, caused by the averaging of individual species effects on function, drives observed patterns. Simulations demonstrate that jack-of-all-trades effects occur whenever species effects on different functions are not perfectly correlated, meaning they may contribute to diversity–multifunctionality relationships in many of the world’s ecosystems.

Insectivorous bats are increasingly recognized as potential regulators of pest insect populations.They also represent the group of European mammals with the most unfavorable conservation status. Forests are key habitats for many bat species but are currently under threat from climate change and fragmentation. It is therefore urgent to better understand the relationships between the bats, their prey and their habitats in forests. Our main objective was to quantify the effects, at multiple spatial scales, of the main attributes of forest habitats on the activity, species richness, functional diversity and composition of European bat communities. They were studied using manipulative experiments in Aquitaine plantation forests and automatic recordings in the network of exploratory plots set up in six European countries by the FunDivEurope project. From the plot to the continent scale, increasing tree diversity, amount of broad leaved trees and dead wood, had positive effects on bat communities through an increase in prey and roost resources. However these effects were not stationary, being stronger at higher latitudes, probably due to lower habitat carrying capacity in relation to harsher climatic conditions. In addition we experimentally demonstrated that the numerical and functional responses of bats to prey density could result in effective regulation of pine processionary moth populations. Forest management strategies aim at enhancing key habitat structures, are eventually proposed in order to improve the conservation of bats and to increase the service of pest regulation they can provide.; Les chiroptères sont reconnus comme de potentiels régulateurs des populations d’insectes. Ce sont aussi les mammifères européens pour lesquels les enjeux de conservation sont les plus importants. Ils trouvent dans les forêts des habitats favorables qui sont cependant menacés par les changements climatiques et la fragmentation. Il convient donc de mieux comprendre lesrelations entre les communautés de chiroptères, leurs habitats et leurs proies en forêt. L'objectif de cette thèse est de quantifier les effets, à différentes échelles spatiales, desprincipales composantes de l’habitat forestier sur l’activité, la richesse spécifique, la diversité fonctionnelle et la composition des communautés de chiroptères européens. Les résultats reposent sur des données collectées grâce à des protocoles expérimentaux en Aquitaine et dans les six pays du réseau de placettes forestières organisé par le projet FunDivEurope. De la parcelle au continent, l'accroissement de la diversité des essences forestières, de la proportion de feuillus et du bois mort, en augmentant les ressources en proies et en gîtes, ont des effets positifs sur les communautés de chiroptères. Ces effets, non stationnaires, se renforcent vers le nord avec la rigueur du climat. Nous confirmons également que les chiroptères forestiers, par leur réponse numérique et fonctionnelle aux densités de proie, peuvent limiter la démographie d’un insecte défoliateur. Des mesures de gestion, visant le renforcement des structures-clés des habitats forestiers, sont proposées pour favoriser la conservation des communautés de chiroptères et leur capacité de régulation des insectes ravageurs.

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International audience; 1- Little is known about the relative effect of different mortality factors triggering the population dynamics of outbreaking Lepidoptera (e.g. climate, natural enemies, habitat diversity), especially at the egg stage. 2- The presence of broadleaved hedgerows bordering pine stands has been shown to reduce infestation by Thaumetopoea pityocampa (Denis & Schiffermüller, Lepidoptera). This effect of habitat diversity has been proposed to result from the disruption of visual and chemical cues that the female moth uses to locate its host. In the present study, we further hypothesized that egg mortality was higher behind broadleaved hedgerows because of higher predation or parasitism, or as a result of harsher microclimatic conditions. 3- A total of 120 egg masses obtained from laboratory rearing were exposed under three exclusion treatments (large predators, predators and parasitoids, no exclusion). Overall egg mortality was 35%. Predation was the main cause of mortality (22%). Mortality as a result of abiotic factors (abortion) was only 12%. Almost no parasitoids were observed. 4- Overall mortality did not differ between pines bordered (or not) by deciduous hedgerows, nor did mortality differ as a result of predation or abortion. 5- Despite an important contribution of predation to mortality in T. pityocampa eggs, the effect of deciduous hedgerows on tree infestation by this pest is more likely to result from disruption of female moth behaviour than from differential mortality.

Les chiroptères sont reconnus comme de potentiels régulateurs des populations d’insectes. Ce sont aussi les mammifères européens pour lesquels les enjeux de conservation sont les plus importants. Ils trouvent dans les forêts des habitats favorables qui sont cependant menacés par les changements climatiques et la fragmentation. Il convient donc de mieux comprendre lesrelations entre les communautés de chiroptères, leurs habitats et leurs proies en forêt. L'objectif de cette thèse est de quantifier les effets, à différentes échelles spatiales, desprincipales composantes de l’habitat forestier sur l’activité, la richesse spécifique, la diversité fonctionnelle et la composition des communautés de chiroptères européens. Les résultats reposent sur des données collectées grâce à des protocoles expérimentaux en Aquitaine et dans les six pays du réseau de placettes forestières organisé par le projet FunDivEurope. De la parcelle au continent, l'accroissement de la diversité des essences forestières, de la proportion de feuillus et du bois mort, en augmentant les ressources en proies et en gîtes, ont des effets positifs sur les communautés de chiroptères. Ces effets, non stationnaires, se renforcent vers le nord avec la rigueur du climat. Nous confirmons également que les chiroptères forestiers, par leur réponse numérique et fonctionnelle aux densités de proie, peuvent limiter la démographie d’un insecte défoliateur. Des mesures de gestion, visant le renforcement des structures-clés des habitats forestiers, sont proposées pour favoriser la conservation des communautés de chiroptères et leur capacité de régulation des insectes ravageurs., Insectivorous bats are increasingly recognized as potential regulators of pest insect populations.They also represent the group of European mammals with the most unfavorable conservation status. Forests are key habitats for many bat species but are currently under threat from climate change and fragmentation. It is therefore urgent to better understand the relationships between the bats, their prey and their habitats in forests. Our main objective was to quantify the effects, at multiple spatial scales, of the main attributes of forest habitats on the activity, species richness, functional diversity and composition of European bat communities. They were studied using manipulative experiments in Aquitaine plantation forests and automatic recordings in the network of exploratory plots set up in six European countries by the FunDivEurope project. From the plot to the continent scale, increasing tree diversity, amount of broad leaved trees and dead wood, had positive effects on bat communities through an increase in prey and roost resources. However these effects were not stationary, being stronger at higher latitudes, probably due to lower habitat carrying capacity in relation to harsher climatic conditions. In addition we experimentally demonstrated that the numerical and functional responses of bats to prey density could result in effective regulation of pine processionary moth populations. Forest management strategies aim at enhancing key habitat structures, are eventually proposed in order to improve the conservation of bats and to increase the service of pest regulation they can provide.

Bats and birds are key providers of ecosystem services in forests. How climate and habitat jointly shape their communities is well studied, but whether biotic predictors from other trophic levels may improve bird and bat diversity models is less known, especially across large bioclimatic gradients. Here, we achieved multi-taxa surveys in 209 mature forests replicated in six European countries from Spain to Finland, to investigate the importance of biotic predictors (i.e. the abundance or activity of defoliating insects, spiders, earthworms and wild ungulates) for bat and bird taxonomic and functional diversity. We found that nine out of 12 bird and bat diversity metrics were best explained when biotic factors were added to models including climate and habitat variables, with a mean gain in explained variance of 38% for birds and 15% for bats. Tree functional diversity was the most important habitat predictor for birds, while bats responded more to understorey structure. The best biotic predictors for birds were spider abundance and defoliating insect activity, while only bat functional evenness responded positively to insect herbivory. Accounting for potential biotic interactions between bats, birds and other taxa of lower trophic levels will help to understand how environmental changes along large biogeographical gradients affect higher-level predator diversity in forest ecosystems.

Plant diversity is an important driver of diversity at other trophic levels, suggesting that cascading extinctions could reduce overall biodiversity. Most evidence for positive effects of plant diversity comes from grasslands. Despite the fact that forests are hotspots of biodiversity, the importance of tree diversity, in particular its relative importance compared to other management related factors, in affecting forest‐associated taxa is not well known. To address this, we used data from 183 plots, located in different forest types, from Mediterranean to Boreal, and established along a climatic gradient across six European countries (FunDivEUROPE project). We tested the influence of tree diversity, tree functional composition (i.e. functional trait values), forest structure, climate and soil on the diversity and abundance/activity of nine taxa (bats, birds, spiders, microorganisms, earthworms, ungulates, foliar fungal pathogens, defoliating insects and understorey plants) and on their overall diversity and abundance/activity (multidiversity, multiabundance/activity). Tree diversity was a key driver of taxon‐level and overall forest‐associated biodiversity, along with tree functional composition, forest structure, climate and soil. Both tree species richness and functional diversity (variation in functional trait values) were important. The effects of tree diversity on the abundance/activity of forest‐associated taxa were less consistent. Nonetheless, spiders, ungulates and foliar fungal pathogens were all more abundant/active in diverse forests. Tree functional composition and structure were also important drivers of abundance/activity: conifer stands had lower overall multidiversity (although the effect was driven by defoliating insects), while stands with potentially tall trees had lower overall multiabundance/activity. We found more synergies than tradeoffs between diversity and abundance/activity of different taxa, suggesting that forest management can promote high diversity across taxa. Our results clearly show the high value of mixed forest stands for multiple forest‐associated taxa and indicate that multiple dimensions of tree diversity (taxonomic and functional) are important.

One of the current advances in functional biodiversity research is the move away from short-lived test systems towards the exploration of diversity-ecosystem functioning relationships in structurally more complex ecosystems. In forests, assumptions about the functional significance of tree species diversity have only recently produced a new generation of research on ecosystem processes and services. Novel experimental designs have now replaced traditional forestry trials, but these comparatively young experimental plots suffer from specific difficulties that are mainly related to the tree size and longevity. Tree species diversity experiments therefore need to be complemented with comparative observational studies in existing forests. Here we present the design and implementation of a new network of forest plots along tree species diversity gradients in six major European forest types: the FunDivEUROPE Exploratory Platform. Based on a review of the deficiencies of existing observational approaches and of unresolved research questions and hypotheses, we discuss the fundamental criteria that shaped the design of our platform. Key features include the extent of the species diversity gradient with mixtures up to five species, strict avoidance of a dilution gradient, special attention to community evenness and minimal covariation with other environmental factors. The new European research platform permits the most comprehensive assessment of tree species diversity effects on forest ecosystem functioning to date since it offers a common set of research plots to groups of researchers from very different disciplines and uses the same methodological approach in contrasting forest types along an extensive environmental gradient. (C) 2013 Elsevier GmbH. All rights reserved.

Many experiments have shown that local biodiversity loss impairs the ability of ecosystems to maintain multiple ecosystem functions at high levels (multifunctionality). In contrast, the role of biodiversity in driving ecosystem multifunctionality at landscape scales remains unresolved. We used a comprehensive pan-European dataset, including 16 ecosystem functions measured in 209 forest plots across six European countries, and performed simulations to investigate how local plot-scale richness of tree species (α-diversity) and their turnover between plots (β-diversity) are related to landscape-scale multifunctionality. After accounting for variation in environmental conditions, we found that relationships between α-diversity and landscape-scale multifunctionality varied from positive to negative depending on the multifunctionality metric used. In contrast, when significant, relationships between β-diversity and landscape-scale multifunctionality were always positive, because a high spatial turnover in species composition was closely related to a high spatial turnover in functions that were supported at high levels. Our findings have major implications for forest management and indicate that biotic homogenization can have previously unrecognized and negative consequences for large-scale ecosystem multifunctionality.

There is considerable evidence that biodiversity promotes multiple ecosystem functions (multifunctionality), thus ensuring the delivery of ecosystem services important for human well-being. However, the mechanisms underlying this relationship are poorly understood, especially in natural ecosystems. We develop a novel approach to partition biodiversity effects on multifunctionality into three mechanisms and apply this to European forest data. We show that throughout Europe, tree diversity is positively related with multifunctionality when moderate levels of functioning are required, but negatively when very high function levels are desired. For two well-known mechanisms, ‘complementarity’ and ‘selection’, we detect only minor effects on multifunctionality. Instead a third, so far overlooked mechanism, the ‘jack-of-all-trades’ effect, caused by the averaging of individual species effects on function, drives observed patterns. Simulations demonstrate that jack-of-all-trades effects occur whenever species effects on different functions are not perfectly correlated, meaning they may contribute to diversity–multifunctionality relationships in many of the world’s ecosystems.

1. Forest ecosystem functioning generally benefits from higher tree species richness, but variation within richness levels is typically large. This is mostly due to the contrasting performances of communities with different compositions. Evidence‐based understanding of composition effects on forest productivity, as well as on multiple other functions will enable forest managers to focus on the selection of species that maximize functioning, rather than with diversity per se. 2. We used a dataset of thirty ecosystem functions measured in stands with different species richness and composition in six European forest types. First, we quantified whether the compositions that maximize annual aboveground wood production (productivity) generally also fulfill the multiple other ecosystem functions (multifunctionality). Then, we quantified the species identity effects and strength of interspecific interactions to identify the ‘best’ and ‘worst’ species composition for multifunctionality. Finally, we evaluated the real‐world frequency of occurrence of best and worst mixtures, using harmonized data from multiple national forest inventories. 3. The most productive tree species combinations also tended to express relatively high multifunctionality, although we found a relatively wide range of compositions with high or low average multifunctionality for the same level of productivity. Monocultures were distributed among the highest as well as the lowest performing compositions. The variation in functioning between compositions was generally driven by differences in the performance of the component species and, to a lesser extent, by particular interspecific interactions. Finally, we found that the most frequent species compositions in inventory data were monospecific stands and that the most common compositions showed below‐average multifunctionality and productivity. 4Synthesis and applications. Species identity and composition effects are essential to the development of high‐performing production systems, for instance in forestry and agriculture. They therefore deserve great attention in the analysis and design of functional biodiversity studies if the aim is to inform ecosystem management. A management focus on tree productivity does not necessarily trade‐off against other ecosystem functions; high productivity and multifunctionality can be combined with an informed selection of tree species and species combinations.

Many experiments have shown that local biodiversity loss impairs the ability of ecosystems to maintain multiple ecosystem functions at high levels (multifunctionality). In contrast, the role of biodiversity in driving ecosystem multifunctionality at landscape scales remains unresolved. We used a comprehensive pan-European dataset, including 16 ecosystem functions measured in 209 forest plots across six European countries, and performed simulations to investigate how local plot-scale richness of tree species (α-diversity) and their turnover between plots (β-diversity) are related to landscape-scale multifunctionality. After accounting for variation in environmental conditions, we found that relationships between α-diversity and landscape-scale multifunctionality varied from positive to negative depending on the multifunctionality metric used. In contrast, when significant, relationships between β-diversity and landscape-scale multifunctionality were always positive, because a high spatial turnover in species composition was closely related to a high spatial turnover in functions that were supported at high levels. Our findings have major implications for forest management and indicate that biotic homogenization can have previously unrecognized and negative consequences for large-scale ecosystem multifunctionality.

Humans require multiple services from ecosystems, but it is largely unknown whether trade-offs between ecosystem functions prevent the realisation of high ecosystem multifunctionality across spatial scales. Here, we combined a comprehensive dataset (28 ecosystem functions measured on 209 forest plots) with a forest inventory dataset (105,316 plots) to extrapolate and map relationships between various ecosystem multifunctionality measures across Europe. These multifunctionality measures reflected different management objectives, related to timber production, climate regulation and biodiversity conservation/recreation. We found that trade-offs among them were rare across Europe, at both local and continental scales. This suggests a high potential for ‘win-win’ forest management strategies, where overall multifunctionality is maximised. However, across sites, multifunctionality was on average 45.8-49.8 below maximum levels and not necessarily highest in protected areas. Therefore, using one of the most comprehensive assessments so far, our study suggests a high but largely unrealised potential for management to promote multifunctional forests.