Abstract Exotic pests and pathogens pose a major threat to forest ecosystems. Early detection of newly introduced organisms is critical for implementing effective eradication measures before they become established. Citizen science platforms have emerged as promising sources of biodiversity data for detecting invasive pests and pathogens, yet their integration into formal biosecurity surveillance remains limited. Using France as a case study, we surveyed 101 professionals involved in forest and urban tree management and pest surveillance to assess their knowledge of regulated tree pests and pathogens and their attitudes towards online citizen science platforms for biosecurity applications. We focused on ten focal species representing different regulatory statuses under EU legislation. We assessed the knowledge professionals have of these species and their regulatory status, and explored sources of variation in their opinions regarding the use of citizen science platforms as a tool for post-border biosecurity. Experts involved in mandatory surveillance of regulated organisms (SORE experts) demonstrated consistent knowledge of quarantine pests, whereas other professionals’ knowledge varied by species, with greater familiarity for non-quarantine, widely distributed pests. Half of respondents used citizen science platforms, predominantly to consult species distribution rather than to contribute observations. Professionals’ receptivity to citizen science increased significantly when species were perceived as easy to identify, but they expressed more confidence in citizen science for monitoring established pests than for the early detection of quarantine species. The survey reveals that while citizen science platforms are known and valued as information sources, they remain underutilized as mechanisms for sharing field observations, even among surveillance professionals.

ABSTRACT Aim The first decade of the 21st century has marked a worsening of anthropogenic climate change which could induce a slowdown in tree growth. However, no consensus has emerged from studies published so far, as positive, negative, or no changes in long‐term tree growth in temperate and boreal forests were locally found. We conducted a meta‐analysis to reveal whether an overall change in tree growth trends has emerged in the last few decades and to determine which factors may have driven any such changes. Location Temperate and boreal forests worldwide. Time Period 1980–2009. Major Taxa Studied Angiosperm and gymnosperm tree species. Methods We performed statistical meta‐regression analyses on the growth of trees in 210 populations gleaned from 62 studies selected after a systematic review of more than 2300 published studies. We calculated effect size values at the population level to compare the slope of tree growth trends over time before and after a given year for each year between 1980 and 2009. We then statistically compared changes in growth among tree species, drought resistance classes, and the position of the species in their climatic niche. Results Estimated effect sizes were close to 0 throughout the end of the 20th century, then dropped from 2005 to 2008 and reached significant negative levels in 2008. Only drought resistance had a significant effect on the increased occurrence of negative effect size values. Main Conclusions Overall tree growth trends remained stable during the last two decades of the 20th century. However, a significant change in tree growth trends occurred during the first decade of the 21st century, with a negative trajectory. Europe most strongly displays this negative change in growth. Drought‐tolerant species were less negatively impacted.

Soil pollution with metals is a worldwide problem with negative effects on ecosystem health. Metals are persistent and can accumulate in the food web, with potential toxic effects for most organisms. Some metal-tolerant plants can accumulate metals in their aboveground parts, including the pollen and nectar of their flowers. Therefore, insects visiting these flowers are exposed to these toxic elements. They can also be influenced by the plant species turnover observed along pollution gradients. Surprisingly, the impact of soil metal contamination on pollinating insect diversity has rarely been studied. To fill in this gap, we carried out a study in a former mining valley in the French Pyrenees with metal contamination by Zn, Pb and Cd. We estimated the richness and community composition of insects visiting the flowers of metal-tolerant and metal-intolerant plant species in 96 plots along metal pollution gradients. Insect richness did not change along the pollution gradient and was similar between metal-tolerant and metal-intolerant plant species. On the contrary, insect community composition changed along the gradient and differed between plant types. We also found that insect species richness increased with the flower abundance of the focal plant. This study showed that flowers of metal-tolerant plants, including hyper-accumulator species, are visited by several insect species and harbour a distinct pollinator community. The ingestion of metal-rich nectar or pollen may have lethal or sub-lethal effects for these flower-visiting insects. Further experimental studies are needed to determine if metal-rich floral resources act as an ecological trap for some of these species.

Invasive forest pests represent a major threat to ecosystems and the economy. They are often first detected in urban forests, making these environments strategic for early warning and global forest protection efforts. Although early detection is crucial to the success of eradication measures, the surveillance capacity of official authorities is limited. Citizen science can help bridge this gap—provided that citizens are aware of the stakes and prepared to play an active role. In this context, mainstream media may serve as a key channel to raise public awareness. We surveyed mainstream media coverage of 14 native, invasive alien non-regulated, and quarantine forest pests across 15 European countries, mostly over the 2011-2024 period. Searching for the scientific or common name of these pests in each national language returned more than 16,000 outputs. While quarantine species were mentioned less frequently than native pests, they were more likely to be mentioned in countries where they have occurred, remain present, or have been eradicated. Interestingly, we also found references to quarantine pests in countries where they were not officially reported. This last finding highlights the potential of mainstream media to attract public attention to tree pests before the surge of an outbreak—an opportunity that should be more systematically leveraged to support early detection and citizen engagement, particularly in cities where the risk of introduction and the potential for early detection is the highest.

Background and Aims Plant-herbivore and plant-pollinator interactions are closely interconnected through their combined influence on plant reproduction, involving both direct and indirect (plant-mediated) effects between these consumer groups. Although these dynamics have been investigated for nearly three decades and were previously synthesized in a meta-analysis, rapid growth in the field in recent years warrants an updated quantitative assessment.Methods We extend the most recent synthesis by incorporating primary studies published between 2018 and 2023, nearly doubling the dataset from 88 to 171 studies and increasing the number of independent observations from 568 to 1348. We reanalysed the effects of both natural and simulated herbivory on floral traits, pollinator visitation and plant reproductive output, expanding previous damage categories to include stem damage and mixed-tissue damage - defined here as damage affecting multiple plant tissues simultaneously (e.g. grazing that impacts both leaves and flowers).Key Results Plant damage significantly reduced floral traits, pollinator attraction and reproductive success. These effects varied with both the type of damage and the tissue affected, with their interaction strongly moderating plant responses. Natural damage to leaves and flowers in most cases reduced floral traits, pollinator visitation and reproduction (except floral traits in the case of flower damage). By contrast, root and mixed damage had no significant effects. Simulated damage, on the other hand, also influenced responses: damage to flowers and stems only reduced floral traits, while damage to leaves reduced pollinator attraction. Importantly, our updated analysis corroborates some trends but also overturns earlier findings: whereas previous work suggested no impact of simulated herbivory, we now detect significant negative effects, and natural floral damage, once considered neutral or in some cases positive for reproduction, is revealed to be detrimental.Conclusions These findings demonstrate that herbivory alters plant-pollinator interactions in trait- and tissue-specific ways, providing new insights into the ecological and evolutionary consequences of plant-herbivore-pollinator linkages.

Sampling methods that are both scientifically rigorous and ethical are cornerstones of any experimental biological research. Since its introduction 30 years ago, the method of using plasticine prey to quantify predation pressure has become increasingly popular in biology. However, recent studies have questioned the accuracy of the method, suggesting that misinterpretation of predator bite marks and the artificiality of the models may bias the results. Yet, bias per se might not be a methodological issue as soon as its statistical distribution in the samples is even, quantifiable, and thus correctable in quantitative analyses. In this study, we focus on avian predation of lepidopteran larvae models, which is one of the most extensively studied predator-prey interactions across diverse ecosystems worldwide. We compared bird predation on plasticine caterpillar models to that on dead caterpillars of similar size and color, using camera traps to assess actual predation events and to evaluate observer accuracy in identifying predation marks a posteriori. The question of whether plasticine models reliably measure insectivorous bird predation remained unanswered, for two reasons: (1) even the evaluation of experienced observers in the posterior assessment of predation marks on plasticine models was subjective to some extent, and (2) camera traps failed to reflect predation rates as assessed by observers, partly because they could only record evidence of bird presence rather than actual predation events. Camera traps detected more evidence of bird presence than predation clues on plasticine models, suggesting that fake prey may underestimate the foraging activity of avian insectivores. The evaluation of avian predation on real caterpillar corpses was probably also compromised by losses to other predators, likely ants. Given the uncertainties and limitations revealed by this study, and in the current absence of more effective monitoring methods, it remains simpler, more cost-effective, ethical, and reliable to keep using plasticine models to assess avian predation. However, it is important to continue developing improved monitoring technologies to better evaluate and refine these methods in order to advance research in this field.

Urban forests provide essential ecosystem services, including pest control, biodiversity conservation, and human health benefits. Herbivory is a widespread biotic interaction that shapes ecosystem functions, such as primary productivity and soil fertility, which underpin these services. Urbanization can disrupt plant–herbivore interactions by altering plant traits, such as nutrient content or phenolic compounds (bottom–up factors), or by changing the abundance of herbivore natural enemies (top–down control), potentially threatening pest regulation and the ecosystem services provided by urban forests. Disentangling these drivers of herbivory is crucial for designing and managing urban forests to enhance resilience. To address this, we examined insect leaf herbivory on Quercus robur trees in urban and rural forest stands across 13 European cities (n = 104 trees). To assess top–down effects on herbivory, we excluded vertebrate (e.g. birds, bats), invertebrate (e.g. ants), or both groups of predators from branches on each tree using different exclosure types. We then measured insect damage on both control and predator‐excluded branches. To evaluate bottom–up drivers, we measured leaf traits, specifically nutrients and phenolic compounds, and tested for correlations with leaf damage. Additionally, we recorded temperature within stands, an abiotic factor that may modulate both top–down and bottom–up forcing on herbivory. Herbivory was 24% lower on urban trees compared to rural trees. In turn, excluding vertebrate (but not invertebrate) predators increased herbivory, on average, by 40%, but predator effects were stronger in urban stands. Urban trees also had higher leaf quality, with higher nutrient and lower phenolic concentrations; however, these traits did not correlate with herbivory. Temperature was positively associated with urbanization and correlated positively with predation, but did not correlate with herbivory and did not mediate the bottom–up or top–down effects of urbanization. Overall, we find that urbanization affects herbivory through both bottom–up and top–down processes, independent of temperature‐related local conditions. Despite stronger predator effects and higher leaf quality, urban trees experienced lower herbivory, suggesting that unmeasured factors, such as changes in herbivore behaviour or community structure, may play an important role. Further studies are needed to deepen our understanding and inform urban forest management.

An increase in biotic interactions towards lower latitudes is one of the most consistent patterns in ecology. Higher temperatures and more stable climatic conditions at low latitudes are thought to enhance biotic interactions, accelerating biological evolution and leading to stronger anti-herbivore defences in plants. However, some studies report contradictory findings, highlighting the need for further investigation into the underlying mechanisms. We used a combination of field observations and feeding trials in controlled environments to investigate the effect of climate on chemical defences and insect herbivory in pedunculate oak (Quercus robur L.) throughout most of its geographic range in Europe, while controlling for physical defences. The concentration of lignin, flavonoids, and total phenolics increased significantly with temperature, whereas both field herbivory and weight of spongy moth (Lymantria dispar L.) larvae were negatively influenced by temperature. Lignin concentration positively influenced the weight of spongy moth larvae whereas it had no effect on field herbivory. We found no evidence of strong positive relationships between insect herbivory and larvae growth with leaf defences. Our study underscores the complexity of plant–herbivore interactions along climatic gradients and highlights the need for further research to disentangle these intricate relationships.

Urbanization is one of the main drivers of biotic homogenization in bird communities worldwide. Yet, only a few studies have addressed its functional consequences on the top-down control birds exert on insect herbivores. We hypothesized that their inconsistent results reflect the overlooked heterogeneity of the urban habitat for birds, and in particular the distribution and diversity of urban trees.We monitored tree diversity, bird diversity, avian predation attempts on artificial prey, and the effect of bird exclusion on insect herbivory in 97 trees distributed among 24 urban experimental plots in the city of Montreal, Canada. We characterized urbanization levels through a combination of variables related to tree density, impervious surfaces, anthropic noise, and human population density.Bird diversity decreased with increasing urbanization, whereas the frequency of generalist synurbic species increased. We found no significant relationship between predation and urbanization or between predation and bird diversity. However, tree diversity was positively correlated with predation attempts on artificial prey, irrespective of bird diversity.We revealed a mismatch between the effects of urbanization on bird diversity and on the regulation service and unraveled the functional importance of tree diversity in shaping the avian predation function in urban ecosystems. Our study advocates for the consideration of intra-urban heterogeneity in the investigation of trophic cascades within cities.

Understanding how tree species mixtures influence forest resistance and resilience to herbivory is critical in the face of global biodiversity loss and climate change. Insect herbivores and their natural enemies respond to changes in forest composition through both bottom-up (e.g., plant traits) and top-down (e.g., predator activity) mechanisms, but their relative importance in Mediterranean mixed forests remains understudied. We assessed insect herbivory and predation rates on cork oak (Quercus suber) in pure and mixed stands with stone pine (Pinus pinea) across seven forest sites in southern Portugal. Tree traits (specific leaf area, SLA; carbon/nitrogen ratio, C/ N; canopy volume; tree height) and understory vegetation characteristics were also recorded. Herbivory was 52 % lower in mixed stand compared to pure stands, although this difference was only marginally significant (p = 0.078). SLA and C/N ratio showed negative trends with herbivory, indicating a potential role of leaf traits in mediating plant resistance. Predation rates did not differ significantly between pure and mixed stands but increased with lower canopy volume and tree height. These findings suggest that plant trait variability contributes to herbivory patterns and that promoting mixed-species stands may strengthen forest resilience. Overall, this study provides valuable insights into the role of tree species mixtures in improving forest resilience and could have significant implications for forest management and biodiversity conservation in Mediterranean ecosystems. Herbivory was 52 % lower in mixed stands compared to pure stands, although this difference was only marginally significant (p = 0.078)

Invasive forest pests are often first detected in urban forests, making these environments strategic for early warning and global forest protection efforts. Although early detection is crucial to the success of eradication measures, the surveillance capacity of official authorities is limited. Citizen science can help bridge this gap — provided that citizens are aware of the stakes and prepared to play an active role. In this context, mainstream media may serve as a key channel to raise public awareness. We surveyed mainstream media coverage of 14 native, exotic, and quarantine forest pests across 15 European countries. Our findings reveal a consistent background level of media attention to forest pest issues. While quarantine species are mentioned less frequently than native pests, they are more likely to be covered in countries where they have occurred, remain present, or have been eradicated. Interestingly, we also found references to quarantine pests in countries where they are not officially reported. Altogether, our exploratory research highlights the significant potential of mainstream media to attract public attention to forest health issues—an opportunity that should be more systematically leveraged to support early detection and citizen engagement.

Invasive, non-native invasive pests pose a growing threat to urban trees and the services they provide to urban residents. With the reluctance to use chemical insecticides in cities, environmentally friendly methods of pest management are needed. Tree diversity is known to affect insect herbivory in forest, with higher tree species diversity leading to lower level of damage. However, the validity of those findings for a non-native insect in an urban environment remains to be demonstrated. We monitored 54 horse chestnut trees attacked by the invasive horse chestnut leafminer Cameraria ohridella in the city of Bordeaux, France. We analyzed the effects of neighboring tree diversity and density on the abundance, damage and parasitism rate of these leafminers. We showed that the abundance and damage of C. ohridella significantly increased with higher local tree canopy cover. We found that the parasitism rate of C. ohridella increased with the species diversity of neighboring trees. However, this increase in parasitism rate was not associated with a decrease in leaf area damaged. Our results pave the way for the management of exotic insect pests in cities based on the manipulation of spatial distribution and species diversity of urban trees.

Tree diversity influences litter decomposition both directly, through changes in litter quality and composition, and indirectly, by altering the local decomposition environment (LDE). However, the role of the LDE in shaping litter decomposition rates remains less explored than the direct effects. A standardized decomposition experiment using cellulose and wood substrates was conducted over the course of a year across seven tree diversity experiments in Europe and North America to explore how tree diversity, through its influence on the LDE, impacts decomposition rates. Tree functional diversity enhanced the decomposition rate of high‐quality substrate (cellulose) but had no effect on the decomposition rate of low‐quality substrate (wood). The impact of LDE was context‐dependent, with decomposition rates being highest under favourable climatic conditions, such as moderate temperatures and high precipitation. Contrary to the common assumption that litter decomposes faster in broadleaved and arbuscular (AM)‐dominated stands, our findings show that decomposition was faster in mixtures containing coniferous species and ectomycorrhizal (EM)‐associated trees, suggesting that LDE plays a larger role than initially thought. Synthesis . This study highlights the crucial role of LDE in shaping decomposition rates. While tree functional diversity generally enhances decomposition under favourable climatic conditions, LDE played a more significant role than previously recognized in EM stands, suggesting that faster decomposition rates in AM stands are primarily due to litter quality. These findings emphasize the context‐dependent nature of decomposition and the importance of considering LDE in understanding how tree diversity influences decomposition processes.

While studies have demonstrated that higher tree species richness can increase forest productivity, the relationships between tree species richness, tree growth and herbivore damage remain insufficiently explored. Here we investigate these linkages using data from 8,790 trees across 80 species in 9 biodiversity experiments, spanning temperate and subtropical biomes. Despite considerable geographic variation, we reveal an overall positive relationship between tree species richness and insect herbivory, as well as between tree growth and herbivory, at individual, species and community levels. The tree growth-herbivory relationship is further influenced by leaf functional traits. In particular, we show that tree species with a higher carbon to nitrogen ratio and, to a lesser extent, tougher leaves, experienced higher herbivory when their growth rate increased. The associations between tree growth and herbivory are further modulated by climatic and soil variation among the sites. Our study highlights the role of functional traits in shaping the relationship between tree growth and herbivory, supporting the resource availability and plant vigour hypotheses.

1. Passive acoustic monitoring has become increasingly popular as a practical and cost-effective way of obtaining highly reliable acoustic data in ecological research projects. Increased ease of collecting these data means that, currently, the main bottleneck in ecoacoustic monitoring projects is often the time required for the manual analysis of passively collected recordings. In this study we evaluate the potential and current limitations of BirdNET-Analyzer v2.4, the most advanced and generic deep learning algorithm for bird recognition to date, as a tool to assess bird community composition through the automated analysis of large-scale ecoacoustic data. 2. To this end, we study 3 acoustic datasets comprising a total of 629 environmental soundscapes collected in 194 different sites spread across a 19 degrees latitude span in Europe. We analyze these soundscapes using both BirdNET and manual listening by local expert birders, and we then compare the results obtained through the two methods to evaluate the performance of the algorithm both at the level of each single vocalization and for entire recording sequences (1, 5 or 10 min). 3. Since BirdNET provides a confidence score for each identification, minimum confidence thresholds can be used to filter out identifications with low scores, thus retaining only the most reliable ones. The volume of ecoacoustic data used in this study did not allow us to estimate species-specific minimum confidence thresholds for most taxa, so we instead used and evaluated global confidence thresholds selected for optimized results when consistently applied across all species. 4. Our analyses reveal that BirdNET identifications can be highly reliable if a sufficiently high minimum confidence threshold is used. However, the inevitable trade-off between precision and recall does not allow to obtain satisfactory results for both metrics at the same time. We found that F1scores remain moderate (<0.5) for all datasets and confidence thresholds studied, and that acoustic datasets of extended duration seem to be currently necessary for BirdNET to provide a reliable and minimally comprehensive picture of the target bird community. We estimate, however, that the usage of species- and context-specific minimum confidence thresholds would allow to substantially improve the global performance benchmarks obtained in this study. 5. We conclude that a judicious use of AI-based identifications provided by BirdNET can represent a powerful method to assist in the assessment of bird community composition through the automated analysis of ecoacoustic data, especially when applied to acoustic datasets of extended duration.

In this study, we measured leaf herbivory by chewing and mining insect herbivores in saplings of nine species of deciduous trees in a warm-temperate montane forest. We censused neighbouring trees and measured five traits known to influence herbivory (i.e., specific leaf area-SLA, thickness, C:N ratio, Na and Si content) on a subset of saplings.