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Many scolytine beetle species have been expanding in new territories, travelling with wood and plants for planting, sometimes with a high impact on plant health. Here, we attempt to quantify the mobility of these species and to identify the biological drivers of mobility and impact. Mobility was estimated by counting the numbers of landmasses (contiguous pieces of land, surrounded by ocean or sea) colonised by each species. A series of potential drivers (taxonomic tribes; feeding regimes; polyphagy; reproductive strategy; host taxa; aggregation pheromones and long-range primary attractants), as well as impact on host health were recorded. A total of 163 species were identified, out of 5546 counted in the whole subfamily. The cosmopolitan taxa amongst the subfamily showed significant disharmony with regards to invasion frequency. Four tribes (Xyleborini; Ipini; Crypturgini; Hylastini) were significantly over-represented and two others (Corthylini; Hexacolini) were under-represented. Some 53% of the 163 species are inbreeding, a very significant excess as compared to the whole subfamily (29%). The inbreeders colonised more landmasses than the outbreeders. There is a significant relationship between the number of host families attacked by a species and the number of colonised landmasses. Most of the invasive species are recorded to respond to long-range host primary attractants, only one quarter respond to pheromones. All very mobile species respond to long-range primary attractants and none is known to respond to pheromones. Very mobile species are all associated with a substantial or moderate impact. The most mobile species belong to a limited number of subtribes. They are often inbreeding, polyphagous and respond to long-range primary attractants, but do not produce pheromones. However, there are many counter-examples. The outbreeding Scolytus multistriatus attacks only three host families, producing aggregation pheromones and has established in thirteen landmasses, with a high impact. Due to these many exceptions, species-based risk prediction relying on the few traits routinely analysed in literature suffers from important uncertainties. [ABSTRACT FROM AUTHOR]

Several time‐series analyses have demonstrated that after extreme summer drought bark beetle damage increased. However, studies predicting stand susceptibility over large spatial extents are limited by technical constraints in obtaining detailed, spatially‐explicit data on infestation spot occurrence.Using a unique dataset of georeferenced bark beetle infestation data, we tested whether the spatial variation of local growing conditions of forest stands, topography, and landscape variables modified the local occurrence of Ips typographus infestations after a severe hot drought in Central Europe.Bark beetle infestation occurrence depended on soil‐related aridity intensity, elevation, slope, and soil conditions. We showed that elevation interacted with growing conditions and topography. At low elevations, spruce forests growing on flat areas and wetter soils were more sensitive to the infestations. On the contrary, forests on steep slopes and soils with low water availability were rarely attacked. At the landscape scale, bark beetle damage increased with host tree cover but decreased with compositional diversity.Our findings are generally consistent with the growth‐differentiation balance hypothesis that predicts that trees growing under chronic dry conditions tend to be more resistant against biotic disturbances.Spruce stands at low elevations located in homogeneous landscapes dominated by spruce were those more exposed to bark beetles in the initial phase of a drought‐induced outbreak. [ABSTRACT FROM AUTHOR]

Associational resistance theory predicts that insect herbivory decreases with increasing tree diversity in forest ecosystems. However, the generality of this effect and its underlying mechanisms are still debated, particularly since evidence has accumulated that climate may influence the direction and strength of the relationship between diversity and herbivory.We quantified insect leaf herbivory and leaf chemical defences (phenolic compounds) of silver birch Betula pendula in pure and mixed plots with different tree species composition across 12 tree diversity experiments in different climates. We investigated whether the effects of neighbouring tree species diversity on insect herbivory in birch, that is, associational effects, were dependent on the climatic context, and whether neighbour‐induced changes in birch chemical defences were involved in associational resistance to insect herbivory.We showed that herbivory on birch decreased with tree species richness (i.e. associational resistance) in colder environments but that this relationship faded as mean annual temperature increased.Birch leaf chemical defences increased with tree species richness but decreased with the phylogenetic distinctiveness of birch from its neighbours, particularly in warmer and more humid environments.Herbivory was negatively correlated with leaf chemical defences, particularly when birch was associated with closely related species. The interactive effect of tree diversity and climate on herbivory was partially mediated by changes in leaf chemical defences.Our findings confirm that tree species diversity can modify the leaf chemistry of a focal species, hence its quality for herbivores. They further stress that such neighbour‐induced changes are dependent on climate and that tree diversity effects on insect herbivory are partially mediated by these neighbour‐induced changes in chemical defences. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Ecological research conducted over the past five decades has shown that increasing tree species richness at forest stands can improve tree resistance to insect pest damage. However, the commonality of this finding is still under debate. In this review, we provide a quantitative assessment (i.e., a meta-analysis) of tree diversity effects on insect herbivory and discuss plausible mechanisms underlying the observed patterns. We provide recommendations and working hypotheses that can serve to lay the groundwork for research to come. Based on more than 600 study cases, our quantitative review indicates that insect herbivory was, on average, lower in mixed forest stands than in pure stands, but these diversity effects were contingent on herbivore diet breadth and tree species composition. In particular, tree species diversity mainly reduced damage of specialist insect herbivores in mixed stands with phylogenetically distant tree species. Overall, our findings provide essential guidance for forest pest management. [ABSTRACT FROM AUTHOR]

Insects appeared more than 400 million years ago and they represent the richest and most diverse taxonomic group with several million species. Yet, under the combined effect of the loss of natural habitats, the intensification of agriculture with massive use of pesticides, global warming and biological invasions, insects show alarming signs of decline. Although difficult to quantify, species extinction and population reductions are confirmed for many ecosystems. This results in a loss of services such as the pollination of plants, including food crops, the recycling of organic matter, the supply of goods such as honey and the stability of food webs. It is therefore urgent to halt the decline of Insects. We recommend implementing long-term monitoring of populations, tackling the causes of insect decline by reducing the use of synthetic insecticides, preserving natural habitats, and reinventing a positive relationship between humans and insects. [ABSTRACT FROM AUTHOR]

The world's forests have never been more threatened by invasions of exotic pests and pathogens, whose causes and impacts are reinforced by global change. However, forest entomologists and pathologists have, for too long, worked independently, used different concepts and proposed specific management methods without recognising parallels and synergies between their respective fields. Instead, we advocate increased collaboration between these two scientific communities to improve the long-term health of forests. Our arguments are that the pathways of entry of exotic pests and pathogens are often the same and that insects and fungi often coexist in the same affected trees. Innovative methods for preventing invasions, early detection and identification of non-native species, modelling of their impact and spread and prevention of damage by increasing the resistance of ecosystems can be shared for the management of both pests and diseases. We, therefore, make recommendations to foster this convergence, proposing in particular the development of interdisciplinary research programmes, the development of generic tools or methods for pest and pathogen management and capacity building for the education and training of students, managers, decision-makers and citizens concerned with forest health. [ABSTRACT FROM AUTHOR]

Pure forests are often seen as being more prone to damage by specialist pest insects than mixed forests, and particularly mixed forests associating host and nonhost species. We addressed the effect of tree diversity on oak colonization and defoliation by a major specialist pest, the oak processionary moth (OPM)We quantified the number of male OPM moths captured and larval defoliation in pure stands of two oak host species (Quercus robur and Quercus petraea) and in mixed stands associating the two oak species or each oak species with another nonhost broadleaved species. We conducted two complementary studies to test the effect of host species and stand composition: (i) we used pheromone trapping to compare the number of males OPM captured throughout the distribution of oak hosts in France and (ii) we noted the presence of OPM nests and estimated defoliation in mature forests of north‐eastern France.Oak species and stand composition significantly influenced the number of male OPM captured and defoliation by OPM larvae. Quercus petraea was consistently more attractive to and more defoliated by OPM than Q. robur. Both oak trees were attacked more in pure stands than in mixed stands, in particular mixed stands associating oaks with another (nonhost) broadleaved species.The results of the present study support the view that mixed forests are more resistant to specialist pest insects than pure stands, and also indicate that this trend depends on forest composition. Our study provides new insights into OPM ecology and has potential implications for forest management, including the management of urban forests where OPM causes serious human health issues. [ABSTRACT FROM AUTHOR]

Tree diversity is increasingly acknowledged as an important driver of insect herbivory. However, there is still a debate about the direction of associational effects that can range from associational resistance (i.e., less damage in mixed stands than in monocultures) to the opposite, associational susceptibility. Discrepancies among published studies may be due to the overlooked effect of spatially dependent processes such as tree location within forests. We addressed this issue by measuring crown defoliation and leaf damage made by different guilds of insect herbivores on oaks growing among conspecific versus heterospecific neighbors at forest edges versus interior, in two closed sites in SW France forests. Overall, oaks were significantly less defoliated among heterospecific neighbors (i.e., associational resistance), at both forest edge and interior. At the leaf level, guild diversity and leaf miner herbivory significantly increased with tree diversity regardless of oak location within stands. Other guilds showed no clear response to tree diversity or oak location. We showed that herbivore response to tree diversity varied among insect feeding guilds but not between forest edges and interior, with inconsistent patterns between sites. Importantly, we show that oaks were more defoliated in pure oak plots than in mixed plots at both edge and forest interior and that, on average, defoliation decreased with increasing tree diversity from one to seven species. We conclude that edge conditions could be interacting with tree diversity to regulate insect defoliation, but future investigations are needed to integrate them into the management of temperate forests, notably by better understanding the role of the landscape context. [ABSTRACT FROM AUTHOR]

The European Food Safety Authority concluded in February 2018 that " most uses of neonicotinoid insecticides represent a risk to wild bees and honeybees ". In 2016, the French government passed a law banning the use of the five neonicotinoids previously authorized: clothianidin, imidacloprid, thiamethoxam, acetamiprid and thiacloprid. In the framework of an expert assessment conducted by the French Agency for Food, Environmental and Occupational Health and Safety to identify possible derogations, we performed a thorough assessment of the available alternatives to the five banned neonicotinoids. For each pest targeted by neonicotinoids use, we identified the main alternative pest management methods, which we then ranked for (i) efficacy for controlling the target pest, (ii) applicability (whether directly useable by farmers or in need of further research and development), (iii) durability (risk of resistance in targeted pests), and (iv) practicability (ease of implementation by farmers). We identified 152 authorized uses of neonicotinoids in France, encompassing 120 crops and 279 pest insect species (or genera). An effective alternative to neonicotinoids use was available in 96% of the 2968 case studies analyzed from the literature (single combinations of one alternative pest control method or product × one target crop plant × one target pest insect). The most common alternative to neonicotinoids (89% of cases) was the use of another chemical insecticide (mostly pyrethroids). However, in 78% of cases, at least one non-chemical alternative method could replace neonicotinoids (e.g. microorganisms, semiochemicals or surface coating). The relevance of non-chemical alternatives to neonicotinoids depends on pest feeding habits. Leaf and flower feeders are easier to control with non-chemical methods, whereas wood and root feeders are more difficult to manage by such methods. We also found that further field studies were required for many promising non-chemical methods before their introduction into routine use by farmers. Our findings, transmitted to policymakers, indicate that non-chemical alternatives to neonicotinoids do exist. Furthermore, they highlight the need to promote these methods through regulation and funding, with a view to reducing pesticide use in agriculture. • Five neonicotinoids were banned in France, which were used to protect 120 crops from 279 pest insect species. • In 96% of cases, neonicotinoids can be replaced by effective and directly useable alternative pest control methods. • In 78% of cases, at least one non-chemical alternative method can replace neonicotinoids. • Leaf and flower feeders are easier to control with non-chemical methods than wood and root feeders. [ABSTRACT FROM AUTHOR]

Abstract: How much a plant is attacked by insect herbivores likely depends on its apparency and ability to produce defensive traits, which may be modified by neighbouring plants and abiotic conditions. Yet, how much the direct and trait‐mediated effects of neighbours on herbivory is modified by abiotic factors is still unknown. By using a tree diversity experiment in SW France, we measured leaf insect herbivory (chewers and miners), nutritional quality (water content, C/N ratio, sugar and starch content) and chemical defences (total polyphenolics and condensed tannins) on birch (Betula pendula) trees growing in monocultures and mixtures with oak, pine or both species. We alleviated water stress by irrigating trees in half of the plots while trees remained unwatered (i.e. drought‐stressed) in the other half. Overall, insect herbivory was higher among heterospecific neighbours, which corresponds to associational susceptibility. Consistent with this finding, leaves had lower amount of anti‐herbivore defences among heterospecific neighbours. In turn, insects caused more damage in drought‐stressed conditions, but such effect was independent of leaf chemistry. We also found that the effect of tree species diversity on herbivory was contingent of drought conditions as associational susceptibility only occurred in drought‐stressed trees. The independent and interactive effects of neighbour diversity and irrigation on leaf herbivory remained significant after accounting for birch apparency and leaf chemistry, suggesting that unmeasured plant traits or some other mechanisms not associated with plant trait variation and apparency might be involved in the observed herbivory patterns. Synthesis. By demonstrating that associational effects are contingent upon abiotic constraints, we bring new insights into our understanding of the mechanisms driving diversity—resistance relationships across climatic gradients. [ABSTRACT FROM AUTHOR]

Abstract: Although insect herbivores and fungal pathogens frequently share the same individual host plant, we lack general insights in how fungal infection affects insect preference and performance. We addressed this question in a meta‐analysis of 1,113 case studies gathered from 101 primary papers that compared preference or performance of insect herbivores on control vs. fungus challenged plants. Generally, insects preferred, and performed better on, not challenged plants, regardless of experimental conditions. Insect response to fungus infection significantly differed according to fungus lifestyle, insect feeding guild, and the spatial scale of the interaction (local/distant). Insect performance was reduced on plants challenged by biotrophic pathogens or endophytes but not by necrotrophic pathogens. For both chewing and piercing‐sucking insects, performance was reduced on challenged plants when interactions occurred locally but not distantly. In plants challenged by biotrophic pathogens, both preference and performance of herbivores were negatively impacted, whereas infection by necrotrophic pathogens reduced herbivore preference more than performance and endophyte infection reduced only herbivore performance. Our study demonstrates that fungi could be important but hitherto overlooked drivers of plant‐herbivore interactions, suggesting both direct and plant‐mediated effects of fungi on insect's behavior and development. [ABSTRACT FROM AUTHOR]

The realized host range of herbivores is expected to increase with herbivore population density. Theory also predicts that trait similarity and phylogenetic relatedness between native and exotic plants is expected to increase the susceptibility of introduced plants to feeding by native herbivores. Whether the ability of native herbivores to extend their host range to introduced species is density dependent is still unknown. We addressed this question by monitoring pine processionary moth (PPM, Thaumetopoea pityocampa) attacks during nine consecutive years on 41 pine species (8 native and 33 introduced) planted in an arboretum. The survey encompassed latent and outbreak periods. A total of 28 pine species were attacked by PPM. There was no difference in the probability of attack between native and introduced pine species. Host range increased and was more phylogenetically clustered during outbreak than latent periods. When population density increased, PPM expanded its diet breadth by attacking introduced pine species that were closely related to native hosts. This study demonstrates the density dependence of host range expansion in a common pine herbivore. Importantly, it supports the idea that the degree of phylogenetic proximity between host species can be a better predictor of attacks than the introduction status, which may help to predict the outcomes of new plant-herbivore interactions. [ABSTRACT FROM AUTHOR]

Theory suggests that the structure of evolutionary history represented in a species community may affect its functioning, but phylogenetic diversity metrics do not allow for the identification of major differences in this structure. Here we propose a new metric, ELDERness (for Evolutionary Legacy of DivERsity) to estimate evolutionary branching patterns within communities by fitting a polynomial function to lineage-through-time (LTT) plots. We illustrate how real and simulated community branching patterns can be more correctly described by ELDERness and can successfully predict ecosystem functioning. In particular, the evolutionary history of branching patterns can be encapsulated by the parameters of third-order polynomial functions and further measured through only two parameters, the “ELDERness surfaces.” These parameters captured variation in productivity of a grassland community better than existing phylogenetic diversity or diversification metrics and independent of species richness or presence of nitrogen fixers. Specifically, communities with small ELDERness surfaces (constant accumulation of lineages through time in LTT plots) were more productive, consistent with increased productivity resulting from complementary lineages combined with niche filling within lineages. Overall, while existing phylogenetic diversity metrics remain useful in many contexts, we suggest that our ELDERness approach better enables testing hypotheses that relate complex patterns of macroevolutionary history represented in local communities to ecosystem functioning. [ABSTRACT FROM AUTHOR]

New (a)biotic conditions, resulting from climate change, are expected to change disturbance dynamics, e.g., wind throw, forest fires and insect outbreaks, and their interactions. Unprecedented natural disturbance 30 dynamics might alter the capability of forest ecosystems to buffer atmospheric CO2 increases in the atmosphere, even leading to the risk that forests transform from sinks into sources of CO2. This study aims to enhance the capability of the ORCHIDEE land surface model to study the impacts of climate change on bark beetle dynamics and subsequent effects on forest functioning. The bark beetle outbreak model is based on previous work by Temperli et al. 2013 for the LandClim landscape model. The new implementation of this model in ORCHIDEE r7791 35 accounts for the following differences between ORCHIDEE and LandClim: (1) the coarser spatial resolution of ORCHIDEE, (2) the higher temporal resolution of ORCHIDEE, and (3) the pre-existing process representation of wind throw, drought, and forest structure in ORCHIDEE. Qualitative evaluation demonstrated the model's ability to simulate a wide range of observed post-disturbance forest dynamics: (1) resistance to bark beetle infestation even in the presence of windthrow events; (2) slow transition (3-7 years) from an endemic into an epidemic bark beetle population following medium intensity window events at cold locations; and (3) fast transition (1-3 years) from endemic to epidemic triggered by strong windthrow events. Although all simulated sites eventually recovered from disturbances, the time needed to recover varied from 5 to 10 years depending on the disturbance dynamics. In addition to enhancing the functionality of the ORCHIDEE model, the new bark beetle model represents a fundamental change in the way mortality is simulated as it replaces a framework in which mortality is conceived as a continuous process by one in which mortality is represented by abrupt events. Changing the mortality framework provided new insights into carbon balance estimates, showing the risk of overestimating the short-term sequestration potential under the commonly used continuous mortality framework. [ABSTRACT FROM AUTHOR]

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., 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., 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., Overall mortality did not differ between pines bordered (or not) by deciduous hedgerows, nor did mortality differ as a result of predation or abortion., 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. [ABSTRACT FROM AUTHOR]

Mixed-species plantation forests are of high interest both because of their potentially superior productivity and multi-functionality benefits over monocultures. However, how trees of different species interact at the canopy level in mixed forests remains unclear, even at young growth stages. We tested whether crown shape and size and stand-level canopy packing were affected by stand composition and how mixture effects varied with stand density and irrigation. We measured crown attributes in pure and mixed plots of two light-demanding species, silver birch (Betula pendula Roth) and maritime pine (Pinus pinaster Ait.), in a 10-year-old tree diversity experiment (ORPHEE). This allowed us to estimate tree-level crown volumes and stand-level canopy packing. We found that (i) at the tree level, stand composition influenced crown-stem allometric relationships in pine but not in birch, (ii) mixture led to greater crown and tree dimensions in pine, but to the opposite for birch, (iii) the changes in crown volume resulted in a higher canopy packing in mixed stands, only at high density and with no irrigation, i.e., under highest constraints for light availability but also soil water availability, contrary to initial expectations. This study sheds light on the effects of water constraints on the aboveground mechanistic processes that explain greater productivity in young mixed plantations, and improves our understanding of canopy packing in mixed stands. [ABSTRACT FROM AUTHOR]

Pest regulation is an important ecosystem service provided by biodiversity, as plants growing in species-rich communities often experience associational resistance to herbivores. However, little is known about the respective influence of the quantity and identity of associated species on herbivory in focal plants., Using a meta-analysis to compare insect herbivory in pure and mixed forests, we specifically tested the effects of the relative abundance of focal tree species and of phylogenetic distance between focal and associated tree species on the magnitude of associational resistance., Overall, insect herbivory was significantly lower in mixed forests, but the outcome varied greatly depending on the phylogenetic relatedness among tree species and the degree of herbivore feeding specialization., Specialist herbivore damage or abundance was positively related to relative abundance of their host trees, regardless of the phylogenetic distance between host and associated tree species., By contrast, tree diversity triggered associational resistance to generalist herbivores only when tree mixtures included tree species phylogenetically distant to the focal species., Synthesis and applications. Our study demonstrates that the establishment of mixed forests per se is not sufficient to convey associational resistance to herbivores if the identity of tree species associated in mixtures is not taken into account. As a general rule, mixing phylogenetically more distinct tree species, such as mixtures of conifers and broadleaved trees, results in more effective reduction in herbivore damage. [ABSTRACT FROM AUTHOR]

Due to climate change, forests are likely to face new hazards, which may require adaptation of our existing silvicultural practices. However, it is difficult to imagine a forest management approach that can simultaneously minimize all risks of damage. Multicriteria decision analysis (MCDA) has been developed to help decision makers choose between actions that require reaching a compromise among criteria of different weights. We adapted this method and produced a multicriteria risk analysis (MCRA) to compare the risk of damage associated with various forest management systems with a range of management intensity. The objective was to evaluate the effect of four forest management alternatives (FMAs) (i.e., close to nature, extensive management with combined objectives, intensive even-aged plantations, and short-rotation forestry for biomass production) on biotic and abiotic risks of damage in eight regional case studies combining three forest biomes (Boreal, Continental, Atlantic) and five tree species (Eucalyptus globulus, Pinus pinaster, Pinus sylvestris, Picea sitchensis, and Picea abies) relevant to wood production in Europe. Specific forest susceptibility to a series of abiotic (wind, fire, and snow) and biotic (insect pests, pathogenic fungi, and mammal herbivores) hazards were defined by expert panels and subsequently weighted by corresponding likelihood. The PROMETHEE ranking method was applied to rank the FMAs from the most to the least at risk. Overall, risk was lower in short-rotation forests designed to produce wood biomass, because of the reduced stand susceptibility to the most damaging hazards. At the opposite end of the management intensity gradient, close-to-nature systems also had low overall risk, due to lower stand value exposed to damage. Intensive even-aged forestry appeared to be subject to the greatest risk, irrespective of tree species and bioclimatic zone. These results seem to be robust as no significant differences in relative ranking of the four FMAs were detected between the combinations of forest biomes and tree species. [ABSTRACT FROM AUTHOR]

In the face of unprecedented loss of biodiversity, cross-taxon correlates have been proposed as a means of obtaining quantitative estimates of biodiversity for identifying habitats of important conservation value. Habitat type, animal trophic level, and the spatial extent of studies would be expected to influence the strength of such correlations. We investigated these effects by carrying out a meta-analysis of 320 case studies of correlations between plant and animal species richnesses. The diversity of arthropods, herps, birds, and mammals significantly increased with plant diversity regardless of species habitat. However, correlations were stronger when plant and animal species richnesses were compared between habitats (γ diversity) than within single habitats (α diversity). For arthropods, both the coefficient of correlation and the slope of the regression line were also greater for primary than for secondary consumers. These findings substantiate the use of plant species richness as an indicator of the diversity of animal taxa over space. [ABSTRACT FROM AUTHOR]

In the context of climate change, the effects of prolonged or more severe droughts on pest and pathogen damage are a major concern for forest ecosystems. To date, there is great uncertainty about the direction, magnitude and sources of variation in responses to drought by insects and fungi. We report the outcomes of a meta-analysis of 100 pairwise comparisons of insect pest or pathogen damage to water-stressed and control trees from 40 publications. The type of feeding substrate for insects and fungi and the water stress severity emerged as the main factors influencing the level of damage in water-stressed trees. Overall, primary damaging agents living in wood caused significantly lower damage to the water-stressed trees compared with the control, whereas primary pests and pathogens living on foliage caused more damage to water-stressed trees, in all cases irrespective of stress severity. In contrast, damage by secondary agents increased with stress severity, which was best estimated by the ratio between the predawn leaf water potential in stressed trees and the xylem pressure inducing 50% loss in hydraulic conductance due to cavitation, a species-specific index of drought tolerance. Insect and fungus feeding behaviour, affected tree part, and water stress severity are therefore proposed as three important predictors of forest damage in drought conditions. [ABSTRACT FROM AUTHOR]

Biodiversity loss from plant communities is often acknowledged to affect primary production but little is known about effects on herbivores. We conducted a meta-analysis of a worldwide data set of 119 studies to compare herbivory in single-species and mixed forests. This showed a significant reduction of herbivory in more diverse forests but this varied with the host specificity of insects. In diverse forests, herbivory by oligophagous species was virtually always reduced, whereas the response of polyphagous species was variable. Further analyses revealed that the composition of tree mixtures may be more important than species richness per se because diversity effects on herbivory were greater when mixed forests comprised taxonomically more distant tree species, and when the proportion of non-host trees was greater than that of host trees. These findings provide new support for the role of biodiversity in ecosystem functioning across trophic levels. [ABSTRACT FROM AUTHOR]

Abstract: We developed a model to predict the dose response pattern in insect captures with sex-pheromone traps. This simulation model enables the testing of three basic assumptions on the links between pheromone dosage and trap catches: (i) the attraction range increases with dose; (ii) for a given dose, the capture size decreases with distance as a logistic function; (iii) for a given distance, the probability that the insect is attracted by the lure increases with dosage. Field data accumulated in our previous studies on the effect of the pheromone dose on the attraction of males of three scale insects –Matsucoccus feytaudi, M. josephi (Hemiptera: Matsucoccidae) and Planococcus citri (Hemiptera: Pseudococcidae) – and on the kairomonal attraction of three predators of M. feytaudi –Elatophilus crassicornis, E. nigricornis (Hemiptera: Anthocoridae) and Hemerobius stigma Stephens (Neuroptera: Hemerobiidae) – was used to validate the model. Additionally, a field trial was conducted in a citrus grove infested by P. citri, in order to assess the parameters of the function that relates probability of capture to distance from the lure. The parameter estimates were subsequently used in the model simulation. The numbers of captures predicted by the model were similar to those observed in the field for all species and sites (r 2 ≥0.91). Model parameters differed according to species but not to site. Differences in population density accounted for the differences in captures observed in different areas. P. citri was an exception to this, in that differences in the male dose response parameters were observed between the tested Portuguese population and the Italian and Israeli populations. The model can be adapted to evaluate information regarding the effect of population size on the maximal attraction distance and trapping efficiency. [Copyright &y& Elsevier]

Summary Recent droughts have strongly impacted forest ecosystems and are projected to increase in frequency, intensity, and duration in the future together with continued warming. While evidence suggests that tree diversity can regulate drought impacts in natural forests, few studies examine whether mixed tree plantations are more resistant to the impacts of severe droughts. Using natural variations in leaf carbon (C) and nitrogen (N) isotopic ratios, that is δ13C and δ15N, as proxies for drought response, we analyzed the effects of tree species richness on the functional responses of tree plantations to the pan‐European 2018 summer drought in seven European tree diversity experiments. We found that leaf δ13C decreased with increasing tree species richness, indicating less drought stress. This effect was not related to drought intensity, nor desiccation tolerance of the tree species. Leaf δ15N increased with drought intensity, indicating a shift toward more open N cycling as water availability diminishes. Additionally, drought intensity was observed to alter the influence of tree species richness on leaf δ15N from weakly negative under low drought intensity to weakly positive under high drought intensity. Overall, our findings suggest that dual leaf isotope analysis helps understand the interaction between drought, nutrients, and species richness. [ABSTRACT FROM AUTHOR]

Enhancing tree diversity may be important to fostering resilience to drought‐related climate extremes. So far, little attention has been given to whether tree diversity can increase the survival of trees and reduce its variability in young forest plantations.We conducted an analysis of seedling and sapling survival from 34 globally distributed tree diversity experiments (363,167 trees, 168 species, 3744 plots, 7 biomes) to answer two questions: (1) Do drought and tree diversity alter the mean and variability in plot‐level tree survival, with higher and less variable survival as diversity increases? and (2) Do species that survive poorly in monocultures survive better in mixtures and do specific functional traits explain monoculture survival?Tree species richness reduced variability in plot‐level survival, while functional diversity (Rao's Q entropy) increased survival and also reduced its variability. Importantly, the reduction in survival variability became stronger as drought severity increased. We found that species with low survival in monocultures survived comparatively better in mixtures when under drought. Species survival in monoculture was positively associated with drought resistance (indicated by hydraulic traits such as turgor loss point), plant height and conservative resource‐acquisition traits (e.g. low leaf nitrogen concentration and small leaf size).Synthesis. The findings highlight: (1) The effectiveness of tree diversity for decreasing the variability in seedling and sapling survival under drought; and (2) the importance of drought resistance and associated traits to explain altered tree species survival in response to tree diversity and drought. From an ecological perspective, we recommend mixing be considered to stabilize tree survival, particularly when functionally diverse forests with drought‐resistant species also promote high survival of drought‐sensitive species. [ABSTRACT FROM AUTHOR]

Tree diversity can promote both predator abundance and diversity. However, whether this translates into increased predation and top‐down control of herbivores across predator taxonomic groups and contrasting environmental conditions remains unresolved. We used a global network of tree diversity experiments (TreeDivNet) spread across three continents and three biomes to test the effects of tree species richness on predation across varying climatic conditions of temperature and precipitation. We recorded bird and arthropod predation attempts on plasticine caterpillars in monocultures and tree species mixtures. Both tree species richness and temperature increased predation by birds but not by arthropods. Furthermore, the effects of tree species richness on predation were consistent across the studied climatic gradient. Our findings provide evidence that tree diversity strengthens top‐down control of insect herbivores by birds, underscoring the need to implement conservation strategies that safeguard tree diversity to sustain ecosystem services provided by natural enemies in forests. [ABSTRACT FROM AUTHOR]

The effects of tree mixture on stand productivity are usually examined using a substitutive approach whereby productivity in mixed stands is compared to productivity in monocultures, at comparable tree density. This approach has proved that mixed stands usually perform better than pure stands. The addition of a second tree species to an existing mono-specific stand has received less consideration. Yet, this approach may separate the facilitation effect from the complementarity effect. We compared the effect of tree species substitution vs. addition on the productivity of maritime pine and silver birch in a 7-year-old tree diversity experiment in south-western France. Given the very young age of the stands, the 2014 tree volumes were used as a proxy for tree productivity. Substituting pines with birches resulted in a significant increase in tree productivity at the stand level, beyond expectations from the weighted mean of monocultures (i.e. overyielding). In contrast, creating a mixture by adding birches to pine stands had no significant effect on the maritime pine productivity: the transgressive mixture effect was not significant. This absence of an effect was produced by two distinct density-dependence responses at the individual tree level. Our results suggest that the addition of a pioneer species with low demands in soil water and nutrients during young developmental stages can diversify stands and increase the provision of ecosystem services without altering the productivity of the target species. [ABSTRACT FROM AUTHOR]

One promising approach to mitigate the negative impacts of insect pests in forests is to adapt forestry practices to create ecosystems that are more resistant and resilient to biotic disturbances. At the stand scale, local stand management practices often cause idiosyncratic effects on forest pests depending on the environmental context and the focal pest species. However, increasing tree diversity appears to be a general strategy for reducing pest damage across several forest types. At the landscape scale, increasing forest heterogeneity (e.g., intermixing different forest types and/or age classes) represents a promising frontier for improving forest resistance and resilience and for avoiding large-scale outbreaks. In addition to their greater resilience, heterogeneous forest landscapes frequently support a wide range of ecosystem functions and services. A challenge will be to develop cooperation and coordination among multiple actors at spatial scales that transcend historical practices in forest management. [ABSTRACT FROM AUTHOR]

Summary: The functioning of present ecosystems reflects deep evolutionary history of locally cooccurring species if their functional traits show high phylogenetic signal (PS). However, we do not understand what drives local PS. We hypothesize that local PS is high in undisturbed and stressful habitats, either due to ongoing local assembly of species that maintained ancestral traits, or to past evolutionary maintenance of ancestral traits within habitat species‐pools, or to both.We quantified PS and diversity of 10 traits within 6704 local plant communities across 38 Dutch habitat types differing in disturbance or stress.Mean local PS varied 50‐fold among habitat types, often independently of phylogenetic or trait diversity. Mean local PS decreased with disturbance but showed no consistent relationship to stress. Mean local PS exceeded species‐pool PS, reflecting nonrandom subsampling from the pool. Disturbance or stress related more strongly to mean local than to species‐pool PS.Disturbed habitats harbour species with evolutionary divergent trait values, probably driven by ongoing, local assembly of species: environmental fluctuations might maintain different trait values within lineages through an evolutionary storage effect. If functional traits do not reflect phylogeny, ecosystem functioning might not be contingent on the presence of particular lineages, and lineages might establish evolutionarily novel interactions. [ABSTRACT FROM AUTHOR]

Many factors can affect the success and failure of classical biological control. However, these factors have mainly been studied independently of each other, which leaves their relative importance within the complexity of classical biological control (CBC) programmes unknown. Therefore, we set out to take a more holistic view on the factors that may impact the outcome of CBC of insect pests by insect predators and parasitoids. To this end, we filtered the BIOCAT catalogue to extract entries for the Greater Western Palearctic ecozone and added 15 new explanatory variables. These mainly concerned traits of released biological control agents, target pests, and host plants of the target, but also included the number of introductions for specific agent-target combinations as a management aspect. We then analysed the data regarding three levels of success: agent establishment, impact on the target population, and complete control of the target. Between 1890 and 2010 a total of 780 introductions of insects for biological control were undertaken in the analysed area, constituting 416 agent-target combinations. Overall success of agent establishment was 32%, successful impact of single agents on their target was 18%, and success of complete control was 11%. The number of factors significantly influencing the outcome of CBC decreased with increasing level of success. Remarkably few agent-related factors influenced the success: insect predators as agents decreased the probability of establishment and using oligophagous parasitoids significantly de- creased the chances of complete control. Other significant factors were related to traits of target pests or their host plants. For example, sap feeders and target pests attacking reproductive plant parts were more likely to be successfully controlled. The rate of success increased with the number of introductions of CBC agents, in particular against univoltine target pests. These findings suggest that a focus on agent-related traits to increase the chances of successful CBC is not fully justified and should be complemented with the consideration of lower trophic levels and other aspects of CBC, such as abiotic factors and management. [ABSTRACT FROM AUTHOR]

The presence of heterospecific neighbours can affect the amount of damage caused by insect pests to focal plants. However, how plant neighbours influence herbivore performance is poorly understood, in particular when they are closely related. We tested the independent and interactive effects of tree species identity and tree neighbour type (conspecific vs. heterospecific) on the performance of a major oak pest, the oak processionary moth larvae (OPM, Thaumetopoea processionea L.) fed on Quercus robur L. and Q. petraea Liebl. We performed a factorial greenhouse experiment in which we grew two oak saplings per pot, either from the same species or from both species. We quantified growth and mortality of OPM larvae, leaf phenolic compounds, C:N ratio and bud phenology. OPM larvae performed significantly better on Q. petraea than on Q. robur, regardless of plant neighbour type. Phenolic compounds and C:N, but not phenology, differed between oak species and neighbour species identity. Only bud phenology had a significant effect on OPM performance, which was better when young larvae had access to recently unfolded leaves, regardless of oak species and neighbour identity. Although oak neighbour identity altered the expression of leaf traits, this effect had no measurable consequences on OPM performance. Our results showed that OPM performed better when feeding on Q. petraea than on Q. robur. We also found that oak neighbours altered the expression of leaf traits associated with defence, but that this effect did not cascade onto OPM performance. These findings should be replicated in the field in order to improve forest management strategies against OPM attacks. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• An individual-based dispersal model was developed for flying pine sawyers. • This model was parameterized with flight mill and mark-release-recapture data. • According to simulations, beetles could fly on average 63 km in total. • Clear-cut zones of 500 m could not prevent the spread of the pine wood nematode. The number of invasive species is increasing throughout the world. One of the corner stones to successfully control them is to better estimate their dispersal capabilities. For flying insects, dispersal performance is commonly estimated through flight mill and mark-release-recapture experiments. However, each approach has its own bias, over- and under-estimating flying distances respectively. The objective of this study was to develop an individual-based dispersal model to circumvent these drawbacks. The shape of the dispersal kernel was calibrated on distances recorded in flight mill experiments (previously done) and then model parameters were fine-tuned based on mark-release-recapture experiments (presented in this study). The pine sawyer beetle, Monochamus galloprovincialis , was used as case study because it is the European vector of the invasive pine wood nematode, Bursaphelenchus xylophilus , recognized as one of the biggest threats to pine forests worldwide. The best fitted model to mark-release-recapture data was parameterized with a mean flying distance of 2000 m per day, which is consistent with flight mill data. It was used to further simulate the dispersal of 100 beetles in non-fragmented pine forests. The cumulative flight distance was 63 km on average at the end of their adult life stage, and the mean dispersal distance as the crow flies was of ca. 13 km. At the end of the maturation period, when most nematodes have been already transmitted to host pines via shoot feeding, about 80% of the insects were located at more than 500 m from the emergence point. These outcomes clearly question the relevance of clear-cut zones of 500 m radius required by the European regulation for the eradication of the invasive nematode. Such dispersal model could be used to support decision-making for eradication programs. [ABSTRACT FROM AUTHOR]

The number of non-native invasive pests and pathogens has increased dramatically in recent years, with disastrous consequences for the health of forests worldwide. Multiple studies have shown that mixed forests may suffer less damage from insect pests than single species forest. This "associational resistance" can be notably explained by the fact that heterospecific neighbours make it more difficult for herbivores to locate and then exploit their host tree. However, the validity of these findings in the case of nonnative, invasive pests and pathogens remains to be demonstrated. In this study, we monitored over two hundred Douglas firs in pure and mixed plots of a tree diversity experiment to assess the damage from the non-native gall midge Contarinia pseudotsugae and the non-native needle cast Nothophaeocryptopus gaeumannii. The probability of Swiss needle-cast infection was lower in Douglas fir trees surrounded by heterospecific neighbours. Gall midge damage was lower on Douglas firs surrounded by taller neighbours, consistent with the hypothesis of reduced host Apparency. Douglas fir trees that were more damaged by C. pseudotsugae were also more often infected by N. gaeumannii. Our study thus provides partial support of the associational resistance hypothesis of mixed forests against exotic pests and pathogens. Promoting forest species diversity at the stand level could, therefore, offer interesting prospects for reducing the impact of biological invasions, especially those involving both pests and pathogens. [ABSTRACT FROM AUTHOR]

When a non-native species succeeds in establishing in a new habitat, one of the possible responses is to attempt its eradication. In the present study, we analysed European eradication programmes against nonnative pests and pathogens of woody plants (PPWP) from 1945 to date. Our main goal was to identify which factors affect the success of an eradication programme, reinforcing guidelines for future eradication of PPWP. Data on eradication campaigns were obtained from online databases, scientific and grey literature, and Plant Protection Organizations' reports. Factors influencing eradication success for both arthropods and pathogens were analysed with LASSO regression and decision tree learning. A total of 848 cases officially declared as eradication attempts were documented in our database (8-fold higher than previous reports). Both the number of programmes and their rate of success increased sharply over the last two decades. Only less than 10% of the non-native organisms affecting woody plants were targeted for attempted eradication despite the high economic and ecological impacts caused by some species for which no efforts were undertaken. Almost one-third of the officially declared cases of eradication concerned organisms that were still restricted to the material with which they were introduced. For these cases the success rate was 100%. The success rate of established species was only 50% for arthropods and 61% for pathogens. The spatial extent of the outbreak was the factor that most affected the outcome of eradication campaigns. The eradication success decreased abruptly above 100 ha for arthropods and 10 ha for pathogens. Additionally, other variables were shown to influence the outcome of eradication programmes, in particular the type of environment, with the highest eradication success rate found in nurseries and glasshouses, with successful outcomes increasing if quarantine measures were applied and when monitoring included asymptomatic plants. Particular species traits may reduce eradication success: parthenogenetic arthropods, saprotrophic pathogens, wind dispersal, the possibility to remain asymptomatic indefinitely, and the existence of resting spores or stages. In conclusion, small affected areas, quick response, and efficient implementation of quarantine restrictions, together with particular species traits, may allow a high probability of eradication success. Preparedness at the country and European level would allow a larger number of target species to be included in future eradication programmes. [ABSTRACT FROM AUTHOR]

Early detection of insect infestation is a key to the adoption of control measures appropriated to each local condition. The use of remote sensing was recommended for a quick scanning of large areas, although it does not work well with signals bearing low intensity or items that are difficult to detect. Unmanned Aerial Vehicle (UAV, or drone) may help in getting closer to individual trees and detect atypical signals of small dimensions. The larvae of the pine processionary moth (PPM, Thaumetopoea pityocampa (Denis & Schiffermüller, 1775, Lepidoptera, Notodontidae) build conspicuous silk nests on the external parts of the host plants at the beginning of the winter and their early detection may prompt managers to adopt management techniques. This work aims at testing two deep learning methods (Region-based Convolutional Neural Network - R-CNN and You Only Look Once - YOLO) to detect the nests under three different conditions of host plant species and forest stands in southern Europe. YOLO algorithm provided better results and it allowed us to achieve F1-scores as high as 0.826 and 0.696 for the detection of presence / absence and the individual nests, respectively. The detection of all the nests that can be present on a tree is not achievable with either UAV scanning or traditional ground observation, therefore the integration of the methods may allow the complete efficiency of the surveillance. The use of UAV combined with Artificial Intelligence (AI) image analysis is recommended for further use in forest and urban settings for the detection of the PPM nests. The recommended methods can be extended to other pest systems, especially when specific symptoms can be associated with an insect pest species. [ABSTRACT FROM AUTHOR]

Emerging and invasive tree pests and pathogens in Europe are increasing in number and range, having impacts on biodiversity, forest services, ecosystems and human well-being. Stakeholders involved in tree and forest management contribute to the detection and management of new and emerging tree pests and pathogens (PnPs). We surveyed different groups of stakeholders in European countries. The stakeholders were mainly researchers, tree health surveyors and forest managers, as well as forest owners, nurseries, policy-makers, advisors, forestry authorities, NGOs and civil society. We investigated which tools they used to detect and manage PnPs, surveyed their current PnP awareness and knowledge and collated the new and emerging PnP species of concern to them. The 237 respondents were based in 15 European countries, with the majority from the United Kingdom, France and the Czech Republic. There was a strong participation of respondents with a work focus on research and surveying, whereas timber traders and plant importers were less represented. Respondents were surveyed on 18 new, emerging PnPs in Europe and listed an additional 37 pest species and 21 pathogen species as potential future threats. We found that species on EPPO's list of 'priority pests' were better known than those not listed. Stakeholders working in urban environments were more aware of PnPs compared to those working in rural areas. Stakeholders' awareness of PnPs was not related to the number of new, emerging PnP species present in a country. Stakeholders want access to more detection and management tools, including long-term citizen-science monitoring, maps showing spread and range of new PnPs, pest identification smartphone apps, handheld detection devices, drone monitoring and eDNA metabarcoding. To help facilitate better forest health across Europe, they called for mixed forest development, reduced nursery stock movement, biosecurity and data sharing amongst organisations. These results indicate that stakeholder knowledge of a few key PnP may be good, but given that the large diversity of threats is so large and future risks unknown, we conclude that multiple and varied methods for generic detection, mitigation and management methods, many in development, are needed in the hands of stakeholders surveying and managing trees and woodlands in Europe. [ABSTRACT FROM AUTHOR]

Current climate change aggravates human health hazards posed by heat stress. Forests can locally mitigate this by acting as strong thermal buffers, yet potential mediation by forest ecological characteristics remains underexplored. We report over 14 months of hourly microclimate data from 131 forest plots across four European countries and compare these to open‐field controls using physiologically equivalent temperature (PET) to reflect human thermal perception. Forests slightly tempered cold extremes, but the strongest buffering occurred under very hot conditions (PET >35°C), where forests reduced strong to extreme heat stress day occurrence by 84.1%. Mature forests cooled the microclimate by 12.1 to 14.5°C PET under, respectively, strong and extreme heat stress conditions. Even young plantations reduced those conditions by 10°C PET. Forest structure strongly modulated the buffering capacity, which was enhanced by increasing stand density, canopy height and canopy closure. Tree species composition had a more modest yet significant influence: that is, strongly shade‐casting, small‐leaved evergreen species amplified cooling. Tree diversity had little direct influences, though indirect effects through stand structure remain possible. Forests in general, both young and mature, are thus strong thermal stress reducers, but their cooling potential can be even further amplified, given targeted (urban) forest management that considers these new insights. [ABSTRACT FROM AUTHOR]

Habitat degradation and climate change are main drivers of insect species loss worldwide, raising concern about natural forest replacement by tree monocultures in a context of more frequent disturbances like drought. Carabid beetles are emblematic species in ecology because they are often used as indicators of biodiversity and they have important functional roles, particularly predation.We used a tree diversity experiment with half of the plots irrigated and the other half under summer water stress to test the combined effects of tree species mixing and drought on carabid species and functional diversity.We observed a qualitative effect of drought on carabid communities, with species turnover mainly due to predator species loss in the drier (non‐irrigated) plots.We also found that species richness and activity density were lowest in pure pine plots and highest in mixture of pine and birch at low tree density. The likely underlying mechanism is the better provision of food and shelter resources in mixed forests.The association of pine with birch species could compensate for the loss of carabid beetles observed between pine monocultures benefiting from the water regime of the last century and those subject to current droughts. This suggests that diversifying plantation forests is a promising way to increase their resilience to the adverse effects of climate change. [ABSTRACT FROM AUTHOR]

The increasing disturbances in monocultures around the world are testimony to their instability under global change. Many studies have claimed that temporal stability of productivity increases with species richness, although the ecological fundamentals have mainly been investigated through diversity experiments. To adequately manage forest ecosystems, it is necessary to have a comprehensive understanding of the effect of mixing species on the temporal stability of productivity and the way in which it is influenced by climate conditions across large geographical areas.Here, we used a unique dataset of 261 stands combining pure and two‐species mixtures of four relevant tree species over a wide range of climate conditions in Europe to examine the effect of species mixing on the level and temporal stability of productivity. Structural equation modelling was employed to further explore the direct and indirect influence of climate, overyielding, species asynchrony and additive effect (i.e. temporal stability expected from the species growth in monospecific stands) on temporal stability in mixed forests.We showed that by adding only one tree species to monocultures, the level (overyielding: +6%) and stability (temporal stability: +12%) of stand growth increased significantly. We identified the key effect of temperature on destabilizing stand growth, which may be mitigated by mixing species. We further confirmed asynchrony as the main driver of temporal stability in mixed stands, through both the additive effect and species interactions, which modify between‐species asynchrony in mixtures in comparison to monocultures.Synthesis and applications. This study highlights the emergent properties associated with mixing two species, which result in resource efficient and temporally stable production systems. We reveal the negative impact of mean temperature on temporal stability of forest productivity and how the stabilizing effect of mixing two species can counterbalance this impact. The overyielding and temporal stability of growth addressed in this paper are essential for ecosystem services closely linked with the level and rhythm of forest growth. Our results underline that mixing two species can be a realistic and effective nature‐based climate solution, which could contribute towards meeting EU climate target policies. [ABSTRACT FROM AUTHOR]

Neonicotinoid insecticides have made possible, for three decades, to protect sugar beet crops against aphids and the viruses they transmit. However, they have been accused of reducing biodiversity, leading the European Union to ban the use of neonicotinoid-coated seeds. The requests for exemptions of use, submitted annually by different member states, might soon no longer be granted. Here, we performed a comprehensive analysis of the available alternatives to neonicotinoids for aphid control in sugar beets, following the PICO framework. The abstracts of 3878 references were consulted to evaluate alternative control methods. Of these, we selected 301 scientific publications, keeping only those which provided indications of treatment efficacy against sugar beet aphids. We identified 75 control strategies (products or methods) as possible alternatives to neonicotinoids. Each control strategy was evaluated based on four criteria: efficacy, durability, applicability and practicability. Using these criteria, we highlight 20 methods or products that have both potential as alternative to neonicotinoids and whose short-term use is feasible. These alternative methods include five synthetic and three natural insecticides, two entomopathogenic fungi, two arthropod natural enemies, organic and mineral oils, two plant defense elicitors, three farming practices and the potential of resistant varieties. Most of them provide important, but arguably insufficient, control of aphids if used alone. However, most of them appear to be complementary and compatible with each other. Therefore, integrating strategies will be needed to maintain beet yields while limiting unintended effects on environment and biodiversity. [ABSTRACT FROM AUTHOR]

Aim: Soil microorganisms are essential for the functioning of terrestrial ecosystems. Although soil microbial communities and functions are linked to tree species composition and diversity, there has been no comprehensive study of the generality or context dependence of these relationships. Here, we examine tree diversity–soil microbial biomass and respiration relationships across environmental gradients using a global network of tree diversity experiments. Location: Boreal, temperate, subtropical and tropical forests. Time period: 2013. Major taxa studied: Soil microorganisms. Methods: Soil samples collected from 11 tree diversity experiments were used to measure microbial respiration, biomass and respiratory quotient using the substrate‐induced respiration method. All samples were measured using the same analytical device, method and procedure to reduce measurement bias. We used linear mixed‐effects models and principal components analysis (PCA) to examine the effects of tree diversity (taxonomic and phylogenetic), environmental conditions and interactions on soil microbial properties. Results: Abiotic drivers, mainly soil water content, but also soil carbon and soil pH, significantly increased soil microbial biomass and respiration. High soil water content reduced the importance of other abiotic drivers. Tree diversity had no effect on the soil microbial properties, but interactions with phylogenetic diversity indicated that the effects of diversity were context dependent and stronger in drier soils. Similar results were found for soil carbon and soil pH. Main conclusions: Our results indicate the importance of abiotic variables, especially soil water content, for maintaining high levels of soil microbial functions and modulating the effects of other environmental drivers. Planting tree species with diverse water‐use strategies and structurally complex canopies and high leaf area might be crucial for maintaining high soil microbial biomass and respiration. Given that greater phylogenetic distance alleviated unfavourable soil water conditions, reforestation efforts that account for traits improving soil water content or select more phylogenetically distant species might assist in increasing soil microbial functions. [ABSTRACT FROM AUTHOR]

Host-plants may rarely leave their ancestral niche and in which case they tend to be surrounded by phylogenetically distant neighbours. Phylogenetically isolated host-plants might share few mutualists with their neighbours and might suffer from a decrease in mutualist support. In addition host plants leaving their ancestral niche might face a deterioration of their abiotic and biotic environment and might hence need to invest more into mutualist partners. We tested whether phylogenetic isolation of hosts from neighbours decreases or increases abundance and activity of their mutualists and whether mutualist activity may help to compensate deterioration of the environment. We study oak-hosts and their ectomycorrhizal fungi mutualists established in the litter layer formed by the phylogenetically closely or distantly related neighbourhood. We find that oaks surrounded by phylogenetically distant neighbours show increased abundance and enzymatic activity of ectomycorrhizal fungi in the litter. Moreover, oaks surrounded by phylogenetically distant neighbours also show delayed budburst but ectomycorrhizal fungi activity partly compensates this negative effect of phylogenetic isolation. This suggests decreased nutrient availability in a phylogenetically distant litter partly compensated by increased litter-degradation by ectomycorrhizal fungi activity. Most observed effects of phylogenetic isolation cannot be explained by a change in baseline soil fertility (as reflected by nutritional status of fresh oak litter, or soil microbial biomass and activity) nor by simple reduction of percentages of oak neighbours, nor by the presence of gymnosperms. Our results show that colonizing new niche represented by the presence of distantly related neighbours may delay plant phenology but may be supported by mycorrhizal mutualists. Studies on other host-plant species are required to generalize our findings. [ABSTRACT FROM AUTHOR]

According to the associational resistance hypothesis, diverse habitats provide better resistance to biological invasions than monocultures. Host-plant abundance has been shown to affect the range expansion of invasive pests, but the effect of landscape diversity (i.e. density of host/non-host patches and diversity of forest habitat patches) on invasions remains largely untested. We used boundary displacement models and boosted regression tree analyses to investigate the effects of landscape diversity on the invasion of Corsica by the maritime pine bast scale Matsucoccus feytaudi over an 18-yr period. Taking the passive wind dispersal of the scale into account, we showed that open habitats and connectivity between host patches accelerated spread by up to 13%, whereas landscapes with high tree diversity and a high density of non-host trees decreased scale spread by up to 14%. We suggest a new mechanism for such associational resistance to pest invasion at the landscape level, which we term 'the pitfall effect'. [ABSTRACT FROM AUTHOR]

Tritrophic interactions among plants, herbivores and predators are expected to be influenced by the surrounding vegetation. Neighbouring plants can influence focal plant colonisation by herbivorous insects and the foraging behaviour of natural enemies, such as insectivorous birds., The aim of the experiment was to disentangle the interactive effects of neighbouring plants and avian predation on arthropod abundance and insect leaf damage in oak tree seedlings, using exclusion cages and vegetation removal., The presence or removal of surrounding herbaceous vegetation differentially mediated top-down effects of insectivorous birds on distinct arthropod guilds and herbivore damage in seedlings. Avian predation reduced sawfly larval abundance regardless of the presence of plant neighbours; lepidopteran larval abundance only when plant neighbours were removed; and spider abundance only when plant neighbours were left intact. The removal of plant neighbours increased prey accessibility for foraging insectivorous birds and decreased chewer damage on seedlings. The density of concealed-feeder insects (leaf miners) increased with plant neighbour removal and when seedlings were less damaged by chewer guild, suggesting intraguild competition., These results highlight the strong indirect effects of neighbouring vegetation on tritrophic interactions involving a focal plant species, its associated herbivores and the upper trophic level of predators. [ABSTRACT FROM AUTHOR]

Two Asian longhorn beetles, Anoplophora glabripennis and Anoplophora chinensis, are among the most serious alien invasive species attacking forest and urban trees, both in North America and Europe. Major efforts have been put into preventing further entry and establishment of the two species as well as promoting their successful eradication. Here, we review these efforts, their progress and outcome, and scientific advancements in monitoring and control methods. The combined international activities and harmonizing legislative changes in detection and eradication methods have proven worthwhile, with more than 45% of eradication programmes successful in the last 12 years. Some countries were able to completely eradicate all populations and others managed to reduce the area affected. Although the costs of the eradication programmes can be very high, the benefits outweigh inaction. Attempts to eradicate A. chinensis have been more challenging in comparison with those targeting A. glabripennis. For both species, efforts are hampered by the ongoing arrival of new beetles, both from their native regions in Asia and from other invaded regions via bridgehead effects. The methods used for eradication have not changed much during the last decade, and host removal is still the method most commonly used. On the other hand, detection methods have diversified during the last decade with advances in semiochemical research and use of detection dogs. The next decade will determine if eradications continue to be successful, particularly in the case of A. chinensis, which has been targeted in some countries for containment instead of eradication. [ABSTRACT FROM AUTHOR]

As of 2020, the world has an estimated 290 million ha of planted forests and this number is continuously increasing. Of these, 131 million ha are monospecific planted forests under intensive management. Although monospecific planted forests are important in providing timber, they harbor less biodiversity and are potentially more susceptible to disturbances than natural or diverse planted forests. Here, we point out the increasing scientific evidence for increased resilience and ecosystem service provision of functionally and species diverse planted forests (hereafter referred to as diverse planted forests) compared to monospecific ones. Furthermore, we propose five concrete steps to foster the adoption of diverse planted forests: (1) improve awareness of benefits and practical options of diverse planted forests among land‐owners, managers, and investors; (2) incentivize tree species diversity in public funding of afforestation and programs to diversify current maladapted planted forests of low diversity; (3) develop new wood‐based products that can be derived from many different tree species not yet in use; (4) invest in research to assess landscape benefits of diverse planted forests for functional connectivity and resilience to global‐change threats; and (5) improve the evidence base on diverse planted forests, in particular in currently under‐represented regions, where new options could be tested. [ABSTRACT FROM AUTHOR]