Publications

The spread of invasive species poses a major threat to global biodiversity, yet predicting successful establishment of exotic species in novel environments remains challenging.

Darwin’s naturalization conundrum is a longstanding debate over whether exotic species closely or distantly related to native communities are more likely to succeed. Despite its long history, empirical studies continue to yield conflicting evidence. Here, we introduce the dark diversity concept, which refers to species that could theoretically inhabit a site but are currently absent.

Combined with observed diversity, dark diversity integrates information on the potential diversity (site-specific species pool size) of the resident community and how completely that pool is locally present (community completeness). Analyzing a 340-y record of successful and failed fish introductions across 516 Swedish lakes, we showed that the effect of phylogenetic relatedness on invasion outcome depends on dark diversity context.

Exotics closely related to resident species were more likely to establish in communities with smaller species pools and higher completeness, whereas phylogenetically distant exotic species were more successful in communities with larger species pools and lower completeness. Models with observed species richness obtained considerably less support. Thus, integrating the dark diversity framework clarifies the contrasting effects of phylogenetic relatedness on invasion outcomes, and helps reconcile this 160-y-old conundrum.

Forest disturbances are increasingly understood as social-ecological phenomena involving diverse actors. Here, we focused on one of the Europe’s largest recent disturbances—the drought-triggered bark beetle outbreak in Central Europe (2017–2022).

Based on a survey of 165 respondents, we examined perceived disturbance drivers, response actions, and the alignment between them as an indicator of a value-action gap that is often present in social-ecological and governance systems. Climatic and forest structure-related factors were identified as the dominant drivers, aligning with current scientific understanding, whereas socio-economic and management constraints were perceived as less influential.

Reported responses reflected awareness of climate-change risks and involved workforce training, adaptive change in species composition, and water-retention measures. Cause–action alignment was observed in nearly half of respondents, particularly among managers and legal entities. We found a relatively sound understanding of disturbance causes and corresponding responses, likely shaped by recent experience with an unprecedented disturbance impact.

Global trade has accelerated the spread of wood-boring insects. Woodwasps (Hymenoptera: Siricidae) include several species that have established outside their native ranges, but their global translocation is not well documented.

Despite several biases, port interception records can serve as indirect proxies of propagule pressure and can be used to quantify invasion pathways. Here, we use historical border interception records from the USA (1914–2020), Canada (1997–2019), and New Zealand (1950–2007) to infer global transport pathways and propagule pressure of siricids. We compiled 3054 interception records, identifying dominant species, source biogeographical regions, and associated commodities. Interceptions were overwhelmingly linked to wood packaging materials, confirming this pathway as the principal vector of introduction.

Most of the intercepted woodwasp species originated from the European and Asian Palearctic regions, indicating these areas as major historical sources of propagule pressure. However, increasing records from non-native regions suggest possible secondary introductions from previously established non-native populations (i.e., bridgehead regions). Despite frequent interceptions, only a subset of species has established, highlighting mismatches between propagule pressure and invasion success, likely mediated by ecological constraints on establishment such as host availability and climate. Our results demonstrate the value of long-term interception datasets for reconstructing invasion pathways, while emphasizing their limitations due to taxonomic uncertainty and sampling bias. Improving species identification and standardizing biosecurity data collection could enhance the use of interception records for invasion risk assessment and management.

Forest wildfires represent a natural phenomenon of forest ecosystem dynamics. However, large-scale forest wildfires are very rare in Central Europe, creating unique habitat conditions for beetles. This study investigated changes in beetle (Coleoptera) communities during the first 2 years after a major wildfire.

Beetles were sampled using a stratified sampling design across six contrasting coniferous forest treatments, including burnt and unburnt sites of (i) bark salvage-logged clear-cuts, and beetle-infested dead-spruce stands,(ii) salvage-logged clear-cuts, and (iii) healthy-forests. A total of 62,128 beetle individuals representing 876 species were identified. Study groups of beetles (all beetles, saproxylic beetles, and non-saproxylic beetles) showed treatment-specific responses during post-fire succession, reflected in both abundance and species richness.

The general trend was a sharp year-over-year decline across most treatments. The strongest declines were observed in burnt clear-cuts and burnt healthy treatments, while burnt dead-spruce treatment showed stable responses. Saproxylic beetles exhibited weaker declines, with slight positive trend recorded in several treatments. In contrast, non-saproxylic beetles consistently declined across all treatments. Among all beetle groups, burnt dead-spruce treatment and unburnt healthy treatment showed the greatest temporal stability.

Although all burnt treatments exhibited strong compositional shifts in beetle communities when compared to their corresponding unburnt sites, wildfire simultaneously promoted convergence of beetle communities across all burnt treatments. During the first post-fire year, gamma diversity showed the highest variability among treatments, whereas in the second year, their species richness and community composition began to converge. Cumulatively within 2 years, fire increased the number of unique species by 170.3% in healthy and 69.8% in dead-spruce but decreased it by 25.1% in clear-cuts compared to unburnt site.

Our extensive study showed that wildfire has a highly site-specific impact on beetle communities in coniferous forests. Each treatment and study group of beetles exhibited distinct post-fire successional dynamics. These findings provide valuable guidance for future forest conservation and management strategies aimed at supporting biodiversity in fire-affected landscapes.

a) Forest disturbances are increasing in many parts of the world. To ensure the continuous provisioning of ecosystem services, a rapid recovery of disturbed sites is frequently an important objective of forest management. However, as management interventions are costly and can have unintended ecological consequences, there is an ongoing debate about whether active post‐disturbance management is necessary to support forest recovery and shape the reorganization of forest ecosystems.

b) Studying forests after the largest disturbance event observed in Central Europe in the past 170 years, caused mainly by drought and subsequent bark beetle outbreaks, we quantified the effect of different post‐disturbance management activities on regeneration outcomes. In 2023, we surveyed 868 plots situated in disturbance hotspot areas across 11 countries to assess the prevalence of different post‐disturbance management activities and evaluate their effects on forest regeneration 3–5 years after disturbance.

c) We found signs of active post‐disturbance management on 93.9% of all surveyed plots. Regeneration cover, sapling density, tree species richness and early‐seral species increased when a combination of management measures—salvage logging followed by tree planting and protection against ungulate browsing—was applied. In contrast, salvage logging alone did not have strong effects on regeneration except shifting species composition towards early‐seral stages. Tree height of post‐disturbance regeneration was not influenced by management.

d) Synthesis and applications. Active management significantly enhanced post‐disturbance tree regeneration in Central European disturbance hotspots. We found that the widespread recuperation of timber value by salvage logging had no detrimental effects on tree regeneration and subsequent stand development. Tree planting and browsing protection reduced the share of Norway spruce—a species increasingly maladapted under climate change—and increased tree species diversity, indicating active climate adaptation in Central European forestry. We conclude that carefully managing the short window of reorganization after disturbance provides high leverage for shaping the future of forests in Central Europe.

In recent years, budburst, the timing of leaf emergence, has advanced less than expected despite continued spring warming, suggesting counteracting ecological forces. One of these forces might be increased and earlier herbivory on young leaves under climate warming.

Here using 5 years of satellite radar data from 27,500 pixels (10 ×10 m2) across 60 temperate oak forest sites under experimental manipulation of insect herbivore loads in Central Europe, we show that prior-year leaf herbivory delayed budburst by 3 days, cancelling the phenological advance observed during a decade of warming.

This delay reduced subsequent herbivory by 55%, exceeding the effects of parasitoids or pathogens, and persisted even during pest outbreaks. Across landscapes, the delay was strongest where it probably provided the highest benefit, that is, where a given amount of delay most effectively reduced following herbivory, which suggests an adaptive tree defence.

Ultimately, trees may be trapped between responding to two opposing consequences of global change: warming selects for earlier budburst, whereas herbivory selects for delay. Our results underscore the need to consider not only climate, but also plant–herbivore interactions and adaptive evolution to predict tree responses to a changing world.

Bark beetle outbreaks pose a severe threat to spruce forests, with the European spruce bark beetle (Ips typographus L.) being the dominant pest in the Czech Republic. Although multispectral imagery using visible (VIS) and near-infrared (NIR) wavelengths has been employed for early detection, it primarily captures visible infestation symptoms rather than the underlying physiological stress, which can, however, be detected using thermal measurements, highlighting the benefit of integrating or complementing multispectral with thermal imagery.

We compared a time series of Unmanned Aerial Vehicle (UAV) based thermal and multispectral imagery over a 650—ha coniferous stand in Central Bohemia, acquired at key phases of infestation (a) a year before infestation (August 2020); (b) closely before bark beetle infestation (April 2021); (c) in the initial phase of the green-attack (May 2021); and (d) in green-attack stage, early detection (June 2021), based on the species phenological model and field survey.

Comparisons of canopy temperature and Normalised Difference Vegetation Index (NDVI) showed that thermal imagery successfully discriminated between healthy and infested trees seven weeks after beetle attack (green-attack), whereas NDVI differences remained negligible.

These results confirm that UAV thermal imaging outperforms multispectral data for the early, individual-tree detection of bark beetle infestation.

Large-scale vegetation height mapping remains a key challenge in remote sensing, with implications for harvest planning, carbon accounting, and habitat assessment. Despite recent methodological advances, limitations persist, including signal saturation in high biomass stands and high preprocessing demands for multi-sensor harmonization.

Advances in artificial intelligence (AI), particularly geospatial foundation models, offer new opportunities to address these limitations. AlphaEarth Foundations (AEF; Google DeepMind, 2025) integrate multi source Earth observation data into compact representations that may alleviate some of these constraints. However, its performance relative to traditional approaches remains unclear. Here, we confronted models trained on AEF embeddings with models trained on conventional optical and SAR features derived from Sentinel-1 and Sentinel-2 data. We tested two modelling approaches – Random Forest (RF) and a deep learning U-Net architecture – resulting in four data–model configurations: AEF+RF, AEF+U-Net, Sentinel+RF, and Sentinel+U-Net.

Vegetation height reference data were derived from UAV-based canopy height models (40 sites; 478 ha). AEF+U-Net significantly outperformed all other configurations with R² = 0.83, RMSE = 1.30 m, and rRMSE = 54.7% (p<0.05, Diebold-Mariano test, K = 40 spatial blocks). Importantly, AEF+U-Net showed greater performance stability across the vegetation height gradient than all other configurations. Beyond predictive accuracy, AEF+U-Net required 29–40% fewer manual preprocessing and feature engineering tasks relative to conventional configurations, further supporting the operational viability of foundation model embedding-based approaches for vegetation structure mapping.

Abstract: Spatial synchrony of population fluctuations has major consequences for the impacts of forest insect pest outbreaks at regional scales.

We tested the predictions that the strength and drivers of this synchrony would differ among species according to their dispersal abilities and feeding guilds. Using a matrix regression approach, we statistically partitioned the importance of spatial and environmental drivers of synchrony in six species of phloem‐feeding bark beetles and six species of defoliating Lepidoptera in North America. Potential drivers included in the regressions were synchrony of weather conditions and spatial proximity.

Overall, model selection operations on the matrix regressions indicated that synchrony in tree damage caused by forest insect pests arises from a combination of drivers including synchrony in weather and spatial drivers such as dispersal. Weather appeared to be more important in driving the synchrony of bark beetles than defoliators, possibly because weather (e.g. drought) has stronger impacts on bark beetle population dynamics. Spatial correlation functions showed that defoliators exhibited stronger synchrony over short distances than bark beetles, possibly because the cyclical nature of defoliator populations allows them to be more easily synchronized.

The greater influence of weather on the synchrony of bark beetles compared to defoliators, coupled with climate‐change driven increases in synchrony of weather, may lead to more widespread events of high tree mortality due to bark beetle epidemics.

Climate change is expected to alter species assemblages by affecting the outcome of competition between species. Investigating processes of competition remains challenging in tree communities, as they unfold over extensive spatio-temporal scales.

Here, we used a deep learning-based meta-model trained on 135 million simulated tree responses to climate across Europe to investigate changes in the competitiveness of nine major tree species under future climate. We harnessed projections from local process models to train a Deep Neural Network of forest state transitions to investigate climate-induced changes in competition at continental scale.

We found decreasing competitive strength for evergreen conifers across their distribution, while deciduous broadleaved species increased in competitiveness. Most investigated species lost competitive strength at their warm range edges. Consequently, up to 25% of Europe’s forests could experience a change in the dominant tree species until the end of the 21st century, suggesting a profound climate-induced reassembly of Europe’s forests.

Ailanthus altissima is an invasive tree species whose persistence and spread in warm, disturbed habitats may be facilitated by its ability to persist under drought conditions. However, it remains unclear whether this ability reflects its high radial-growth resistance to drought or rapid post-drought recovery.

We analysed tree-ring chronologies from a dry lowland region in Slovakia to quantify climate-growth relationships and drought resilience using sliding-window analysis and resistance-recovery indices. Major drought events since 1950 were identified in 1993, 1998, 2003, 2007, 2012 and 2017. Radial growth was most strongly associated with precipitation, whereas temperature amplitude had a weaker effect. Growth declined most strongly under low precipitation and high temperature amplitude, indicating substantial sensitivity of radial growth to water deficit.

Median RWI-based resistance values were approximately 0.7-0.8, corresponding to a 20-30% reduction in growth during drought years relative to expected growth, whereas recovery indices generally exceeded 1.2 over the following two years, indicating rapid post-drought growth recovery. These results show that A. altissima is not insensitive to drought, but rather combines moderate drought-induced growth reductions with high recovery capacity. Such a resilience-based drought strategy may contribute to its persistence in dry lowland forests and sustain invasion risk where disturbance and canopy openings provide opportunities for establishment.

Propagule pressure is one of the key drivers of establishment success of non-native species, including insects. However, border interception data, which have the potential to act as a proxy for true arrival rates (i.e., propagule pressure) of insects into a country, are seldom used to predict invasions.

This can be due to the limited amount of interception data in some countries, difficulties accessing such data, and when these data are available, difficulties in addressing biases caused by variation in interception probability for different taxa due to policy changes, and operational influences of import inspections. The type of interception data required to reliably estimate arrival rates is rarely available.

To improve the use of interception data as a proxy for propagule pressure, we investigated the fraction of established species which had interceptions and vice versa by taxonomic group and by biological characteristics (development type and feeding group), using several national datasets from five continents. We identified higher fractions of established species that were intercepted for plant feeding insect groups compared to fractions of non-plant feeding groups, even in countries with more general import inspection strategies. This is likely to reflect greater search effort for and recording of plant-feeding insect groups during inspections.

To address this variation in interception probability and improve establishment predictions based on interception frequency, we developed a methodology to account for such taxonomic variation. We apply this to three hazard lists of insects, containing potential pests for an industry or potential pests for a country, to assess its effectiveness.

Biological invasions are one of the major drivers of biodiversity decline and have been shown to have far-reaching consequences for society and the economy. Preventing the introduction and spread of alien species represents the most effective solution to reducing their impacts on nature and human well-being.

However, implementing effective solutions requires a good understanding of where the species are established and how biological invasions develop over time. Knowledge of the status and trends of biological invasions is thus key for guiding research efforts, informing stakeholders and policymakers, for targeted management efforts, and preparing for the future. The high dynamism of alien species introductions and spread complicates the task of providing up-to-date and accurate assessments of the status of biological invasions across the world.

We present results of a comprehensive assessment of the historical trends and current distributions of alien species across geographic regions worldwide, based on the most comprehensive global database of alien species. We describe global patterns in the richness and composition of alien species and their trends across multiple taxonomic groups and geographic regions. We discuss methodological challenges such as inconsistencies in reporting, knowledge gaps and data availability. We identify data-poor regions and taxa and provide guidance on how these can be addressed to improve biological invasion assessments.

Herbivores are commonly classified as host specialists or generalists for various purposes, yet the definitions of these terms, and their intermediates, are often imprecise and ambiguous.

We quantified host breadth for 240 non-native, tree-feeding insects in North America using phylogenetic diversity and demonstrated that a partitioning of host breadth: (1) causes 67% of non-native insects to shift from a generalist to specialist category, (2) displays a reduction in host breadth from the native to introduced range, (3) identifies an inflection point in a model predicting the likelihood of non-native insect ecological impact, with a corresponding change in behaviour associated with specialists versus generalists, and (4) enables three models for strong prediction of whether a non-native forest insect will cause high impacts.

Together, these results highlight the primacy of how herbivore host recognition and plant defences mediate whether novel host interactions will result in high impact after invasion.

Bark beetle-induced tree mortality has increased strongly in Europe in recent years. Bark beetle populations are highly sensitive to temperature, and drought weakens tree defenses against beetle attacks. Yet, the compound effects of drought and heat (termed hotter drought) remain poorly quantified, even though climate change increases their joint occurrence.

Here, we analyzed data from a regional-scale network of pheromone-baited Ips typographus traps (158 traps across 7 Mha in southeast Germany, with 67.5 million beetles caught between 2015 and 2021), contrasting the unprecedented hotter drought period of 2018–2020 with non-drought years. Our objectives were (i) to assess the effect of hotter drought on bark beetle population dynamics, (ii) to quantify changes in spatial patterns during hotter drought, and (iii) to investigate how well trap data can explain observed tree mortality.

Bark beetle population levels were strongly driven by temperature and drought, with an annual increase of approximately 2000 beetles per trap per °C under drought conditions (SPEI = −1). Furthermore, critical phenological thresholds were reached 7 days earlier for aggregation and 4 days earlier for peak swarming timing per °C increase in temperature. In drought years, I. typographus population levels were autocorrelated across hundreds of kilometers. Trap data explained between 37% and 49% of observed bark beetle mortality, highlighting that pheromone trap networks are a useful tool for monitoring and managing forest risk.

We conclude that hotter drought intensifies and extends mass outbreaks of the European spruce bark beetle, suggesting the emergence of novel patterns of disturbance.

While numerous allometric models exist for estimating biomass in trees with single stems, models for multi-stemmed species are scarce. This study presents models for predicting aboveground biomass (AGB) in European hazel (Corylus avellana L.), growing in multi-stemmed shrub form.

We measured the size and harvested the biomass of 30 European hazel shrubs, drying and weighing their woody parts and leaves separately. AGB (dry mass) and leaf area models were established using a range of predictors, such as the upper height of the shrub, number of shoots per shrub, canopy projection area, stem base diameter of the thickest stem, and the sum of cross-sectional areas of all stems at the stem base. The latter was the best predictor of AGB, but the most practically useful variables, defined as relatively easy to measure by terrestrial or aerial approaches, were the upper height of the shrub and the canopy projection area.

The leaf biomass to AGB ratio decreased with the shrub's height. Specific leaf area of shaded leaves increases with shrub height, but that of leaves at the top of the canopy does not change significantly. Given that the upper shrub height and crown projection of European hazel can be estimated using remote sensing approaches, especially UAV and LiDAR, these two variables appear the most promising for effective measurement of AGB in hazel.

Rachel Carson's warning of a silent spring directed attention to unwanted side effects of pesticide application. Though her work led to policies restricting insecticide use, various insecticides currently in use affect nontarget organisms and may contribute to population declines. The insecticide tebufenozide is used to control defoliating Lepidoptera in oak forests harboring rich insect faunas.

Over 3 years, we tested the effect of its aerial application on bird populations with autonomous sound recorders in a large, replicated, full factorial field experiment during a spongy moth (Lymantria dispar) outbreak. The soundscape analysis combined automated aggregation of recordings into sound indices with species identification by experts. After pesticide application in the year of the outbreak, acoustic complexity in early summer was significantly reduced. The soundscape analysis showed that the reduction was not related to birds, but instead to the large reduction in caterpillar feeding and frass dropping. Effects on the vocal activity of birds were smaller than originally expected from a related study demonstrating tebufenozide's negative effect on bird breeding success.

The legacy of the pesticide treatment, in terms of soundscape variation, was not present in the second year when the outbreak had ended. Our results showed a dimension of insecticide-induced acoustic variation not immediately accessible to the human ear. It also illustrated how a multifaceted soundscape analysis can be used as a generic approach to quantify the impact of anthropogenic stressors in novel ways by providing an example of remote and continuous sound monitoring not possible in conventional field surveys.

Forest tree diversity helps shape the assembly of herbivorous insect communities in forests worldwide, and Island biogeography theory explains the role of tree range area as a driver of variation in native insect richness per tree species. However, it is unclear if these biogeographical principles apply to non-native insect herbivores.

We created an extensive list of tree–insect associations for tree species native to Palearctic Europe bioregion and investigated how both native and non-native insect herbivore species richness per tree may be influenced by various factors including the range area of the tree and the tree type (conifer or angiosperm). Models were further subsetted to compare drivers for the richness of different feeding guilds (folivores, sap feeders or wood borers) and host breadth (specialist or generalist).

Tree range area had a positive effect on native, but not non-native, insect species richness per tree, while non-native richness was affected by host type and had a positive correlation with native herbivore richness on the same tree species. Host breadth grouping did not influence the difference in the effect of tree range on native versus non-native insect richness, but native folivores had a stronger relationship with range distribution area compared to the other groups. We conclude that the assembly of non-native herbivorous insect species on trees occurs through fundamentally different mechanisms than the co-evolutionary processes proposed by the framework of Island biogeography theory.

The majority of non-native animal species globally are insects, though some insect species are more successful invaders than others. These differences can be attributed, in part, to differences among dominant trophic groups. Previous analyses indicate that insect herbivores are generally over-represented among non-native species while other groups, such as predators, are under-represented. Here we explore how invasion success varies among insect taxa and trophic groups.

We quantify over-representation in species grouped by taxon (order or family) and larval trophic group (herbivore, detritivore, predator, parasite, brood carer); over- and under-representation is computed by comparing proportional representation of groups among non-native species in 12 world regions with total numbers in these same groups globally. Although herbivores are generally the most successful group among non-natives, we found their invasion success to vary among their taxonomic groups: herbivores are over-represented among Hemiptera, Diptera, Thysanoptera and Hymenoptera, but under-represented among Lepidoptera and Orthoptera; similar patterns are seen at the family-level within orders.

Even after accounting for trophic group, some orders were still over-represented. Further analyses suggest that factors other than trophic group, such as associations with invasion pathways (e.g., plants, wood packaging), cause the observed differences in the over-representation of families belonging to different orders.

Aim: Predicting climate driven species range shifts requires knowledge of mechanisms limiting species fitness under various climatic conditions. The traditional approach of modelling ranges of herbivorous insects by fitting environmental niche models to occurrence records is generally incapable of differentiating direct effects of climate on insect populations versus indirect effects acting on the range of their host plants. Here, we delimit the southern extent of a major forest defoliator, the spruce budworm, Choristoneura fumiferana, in North America, and investigate whether its range is limited directly by climate or indirectly by the range of its host trees.

Location: Eastern North America.

Methods: We use pheromone traps to survey populations; these are sensitive tools for detecting low-density populations. We applied mechanistic models of the effect of temperature on C. fumiferana to estimate what would be the range if it were limited by climate alone.

Results: Pheromone trap surveys indicated that populations were broadly distributed across the southern Appalachian Mountains, far south of the known range limit of the primary host tree, balsam fir, Abies balsamea. Mechanistic temperature-based models predict conditions suitable for C. fumiferana as far south as Tennessee and North Carolina. Main Conclusions: Our results indicate that the range of C. fumiferana extends beyond the range of its primary host and that climate is a more important determinant of range limits than host availability. This finding confirms that there are populations that are not visible from aerial detection surveys using conventional defoliation-based sampling and that future range expansion is likely driven by direct climate effects.

Until it was discovered in Boulder, Colorado in 2013, the invaded range of the emerald ash borer, Agrilus planipennis, in the Western Hemisphere was entirely limited to natural and urban forests of eastern North America. Subsequently, this species has expanded its range through much of the Colorado Front Range region, utilizing non-native ash, Fraxinus spp.

These host trees are widely planted there in urban settings but natural forests containing ash are lacking in the region. Here we use survey data to quantify emerald ash borer regional spread across the Colorado Front Range as well as its local spread in the city of Longmont, Colorado.

Across the region, spread rate was estimated at 3.9 km/yr, but within Longmont the rate was only 0.25 km/yr. These rates of spread are lower than what has been reported from comparable spatial scales in eastern North America and the slower spread may reflect reduced host resource availability, successful implementation of management, or differences in insect dispersal behavior. The pattern of spread in Longmont is further characterized by the formation of satellite populations that subsequently merged with the expanding invasion front.

Intensive forestry, particularly clear-cutting, is the primary threat to biodiversity in boreal forests. While forest conservation efforts aim to protect valuable forests, it remains uncertain whether these efforts are effectively safeguarding them in the long-term.

To address this question, we assessed whether the most valuable forests in terms of biodiversity conservation are still being lost due to recent harvesting. Using the national map of high biodiversity value forests, we compared the biodiversity values of harvesting sites with those of all forests across Finnish administrative regions. Additionally, we assessed the extent of harvesting and protection within the top 10% of forests with the highest biodiversity value. We used two complementary sources of harvesting data: the Global Forest Change data, showing annual loss of forest cover based on Landsat satellite images, and compulsory forest use notifications filed prior to forestry operations.

Our findings indicate that the biodiversity values of harvesting sites increase from north to south and are slightly higher than the average biodiversity values of all forests across all regions. Approximately one-third of the top 10% of forests with the highest biodiversity value are currently protected. Our results show that harvesting affects all forests outside of protected areas irrespective of their biodiversity value. Evaluating the extent of harvest in high biodiversity value forests is essential for assessing the success of current conservation practices and planning future measures.

Bats are important but threatened insectivorous predators, making them a core group to consider when weighing the risks and benefits of insecticide use for combating pest outbreaks. Bats may benefit from open spaces created when insect pests defoliate tree canopies. Applying insecticides could also make treated areas less attractive to bats by lowering insect availability and increasing canopy densities.

Here, we examined the effects of a one-time insecticide treatment of oak forest plots with tebufenozide under outbreak and non-outbreak scenarios of the forestry pest species Lymantria dispar in a full-factorial and well-replicated field experiment. The activity of all bats and of closed-, edge- and open-space foragers was measured at 44 plots over 3 years using autonomous acoustic bat recorders. We simultaneously estimated the biomass of available flying insect prey using light trapping and quantified changes in tree canopy density using satellite-based radar.

Contrary to our expectations, we found higher bat activity in insecticide-treated plots than in untreated plots, including plots with predicted L. dispar outbreaks. There was no overall prey reduction at treated plots. Moreover, the high canopy density, particularly at treated plots, likely promoted biomass of non-moth, non-beetle flying insects. This suggests that bats, especially open-space foragers, responded to the increasing availability of other insects at treated plots with a higher canopy density, rather than to a decrease in prey availability.

Synthesis and applications: L. dispar drastically decreased the canopy density of outbreak plots, whereas insecticide treatment protected the tree canopy from defoliation. However, bats were not promoted by lower canopy density, and there was no decrease in insect prey availability between plots. Bats continued to be active at forest plots treated with tebufenozide, which may be due to insect prey harboured in the denser tree foliage at these plots. Overall, we did not observe the expected strong negative response of bat activity to tebufenozide treatment when using acoustic bat monitoring. However, there may be other risks to consider, such as pesticide exposure and food web alterations, which must be evaluated using different methods.

Recent increases in forest damage across Europe have challenged national forestry sectors and threatened progress toward Europe's climate and bioeconomy goals. Although developments in remote sensing now allow large-scale wall-to-wall monitoring of forest conditions, reliable damage assessments still require robust terrestrial data. Yet, existing data often remain inconsistent and fragmentarily distributed across institutions and countries.

Based on consultations with national experts, we here provide an evaluation of national forest damage survey programmes in 19 European countries, identify obstacles that hinder more effective use of data, and formulate recommendations to overcome these barriers. We examined five aspects of national forest damage surveys: (i) legal and institutional frameworks, (ii) data acquisition methods, (iii) damage attribution, (iv) data quality and consistency, and (v) data accessibility.

We found that half of the examined programs have changed protocols since 2000 and only 53% of countries currently have survey programs covering their entire forest area. In 26% of countries, legal constraints hamper data accessibility to the broader international community, while in 89% data are available only in the respective national languages. In 84% of countries, the absence of adequate metadata hinders the usability of the data without inside knowledge. Some of Central European countries operate the most consistent and open systems, while western and northern countries generally exhibited lower levels of openness and consistency.

The implementation of coordinated structural changes in national programs that would enable consistent monitoring of forest damage at European level is unrealistic in the foreseeable future. However, certain critical gaps in data coverage, completeness, and consistency can be addressed through extensive data post-processing and integration with remote sensing. Overcoming barriers, such as limited awareness of the importance of transnational assessments, requires improved communication efforts and targeted funding programs. Establishing a coordination unit by leveraging existing policy processes in Europe appears essential to advancing these efforts.

Ongoing shifts in climate and land use have altered interactions between trees and insect herbivores, changing biotic disturbance regimes. However, as these changes are complex and vary across host species, insect taxa, and feeding guilds, they remain poorly understood.

We compiled annual records of forest insect disturbance from 15 countries in temperate and boreal Europe, spanning the period from 2000 to 2022. The dataset comprises 1361 time series characterizing the dynamics of 50 herbivorous insects. We used this dataset to test whether insect disturbance has systematically changed during the 23-year period across host trees and feeding guilds, whether it varies along latitudinal and climatic gradients, and whether synchrony exists among species in the same guild or among species sharing the same host. Since 2000, borer disturbance was predominantly concentrated on gymnosperms, while defoliators impacted gymnosperms and angiosperms more evenly.

While 85.8% of gymnosperm disturbance was inflicted by a single species, Ips typographus, the majority of disturbances to angiosperms were caused by six different species. Borer impact on gymnosperms has increased in the 21st century, while defoliator impact has decreased across both clades. In contrast to diverging temporal trends, disturbance was consistently greater in warmer and drier conditions across feeding guilds and host types. We identified significant synchrony in insect disturbance within host types and feeding guilds but not between these groups, suggesting shared drivers within guilds and host types. Increasing insect disturbance to gymnosperms may catalyze adaptive transformations in Europe's forests, promoting a shift from historical conifer-dominated management to broadleaved trees, which are less affected by insect herbivores.

Our findings reveal a diversity of trends in insect herbivory, underscoring the need to strengthen monitoring and research in order to better understand underlying mechanisms and identify emerging threats that may not be apparent in currently available data.

Spatial synchrony of population fluctuations has major consequences for the impacts of forest insect pest outbreaks at regional scales. We tested the predictions that the strength and drivers of this synchrony would differ among species according to their dispersal abilities and feeding guilds.

Using a matrix regression approach, we statistically partitioned the importance of spatial and environmental drivers of synchrony in six species of phloem-feeding bark beetles and six species of defoliating Lepidoptera in North America. Potential drivers included in the regressions were synchrony of weather conditions and spatial proximity. Defoliator outbreaks showed notably stronger spatial synchrony than bark beetle outbreaks. Meteorological synchrony was the primary driver of defoliator synchrony and a more minor driver of bark beetle synchrony.

The stronger synchrony of defoliators is probably not due to their greater dispersal ability, as bark beetle species with greater dispersal ability did not exhibit stronger synchrony. Our results suggest that the high degree of synchrony of defoliator outbreaks is primarily driven by synchronous variation in weather conditions across regions and not by dispersal. These findings highlight the importance of meteorological factors in shaping defoliator outbreak dynamics while also underscoring fundamental differences in the drivers of synchrony between feeding guilds.

The rising introduction of invasive species through trade networks threatens biodiversity and ecosystem services. Yet, we have a limited understanding of how transportation networks determine spatiotemporal patterns of range expansion. This knowledge gap may stem from two reasons. First, current analytical models fail to integrate the invader's life-history dynamics with heterogeneity in human-mediated dispersal patterns. Second, classical statistical methods often fail to provide reliable estimates of model parameters due to spatial biases in the presence-only records and lack of informative demographic data.

To address these gaps, we first formulate an age-structured metapopulation model that uses a probability matrix to emulate human-mediated dispersal patterns. The model reveals that an invader spreads along the shortest network path, such that the inter-patch network distances decrease with increasing traffic volume and reproductive value of hitchhikers. The model predicts non-monotonic spread dynamics as function of reproductive value. Second, we develop a Bayesian inference framework using spatio-temporal presence records and short-term population estimates to estimate the parameters governing life-history, dispersal, and time of introduction.

We validate this framework by applying it to a well-studied invasion case: zebra mussels (Dreissena polymorpha) in US inland water bodies, where their spread is facilitated by recreational boating. We demonstrate that the framework recovers life history and dispersal parameters with minimal sampling bias and provides reliable estimates of invasion start time. The developed framework provides a means to characterize the invasion dynamics of species spread by human transportation systems.

Context: Historically, large-scale outbreaks of the European spruce bark beetle were initiated mainly by windthrows. However, after 2018, a severe drought triggered the hitherto largest bark beetle outbreak observed in Europe, signalling a major shift in the disturbance regime.

Objectives: Develop and test an approach that allows simulating this novel disturbance dynamics and evaluate landscape-scale compound impacts of wind- and drought-initiated outbreaks throughout the twenty-first century.

Methods: We incorporated drought-initiated outbreaks into the forest landscape simulation model iLand, using critical values of vapour pressure deficit as the outbreak trigger. Forest management records and remote sensing-based disturbance maps were used to derive model parameters and evaluate simulated dynamics in a Central European forest landscape (4,916 ha) in Czechia for 1961–2021 and under climate scenarios until 2100. Results: Incorporating drought as outbreak trigger led to a notable decoupling of wind and bark beetle disturbances, which have historically formed a typical disturbance cascade in European forests. While forest growing stock and species composition were resilient to a wind-dominated disturbance regime, this resilience diminished under the compounded impact of wind- and drought-triggered disturbances. The new disturbance regime caused a persistent decline in Norway spruce and resulted in an overall decrease in landscape-level growing stock.

Conclusions: Our findings underscore the urgent need for new approaches to evaluate increasingly complex disturbance dynamics and suggest that the future impacts of bark beetles on forest landscapes may be greater than previously anticipated.

Context: Following the hot and dry year of 2018, European forests underwent an unprecedented wave of disturbances. The subsequent recovery phase is indicative of ecosystem resilience and critical for long-term forest development; however, the landscape-scale manifestation of these processes remains poorly understood.

Objectives: Quantify forest disturbance and early recovery dynamics across a 9000-km2 forested landscape (Central Europe, Czech Republic) following an extensive outbreak of spruce bark beetle and subsequent treatment by extensive salvage logging and replanting.

Methods: We integrated optical and Synthetic Aperture Radar remote sensing data with very high-resolution UAV imagery and derived vegetation height models to map disturbance impacts and post-disturbance recovery patterns from 2018 to 2024.

Results: Between 2018 and 2024, 30.8% of the initial forest area was disturbed. Within the disturbed areas, bare soil dominated, indicating a lack of understory in the pre-disturbance forest and the high intensity of removal of disturbance legacies. Temporary regeneration failures, i.e., transitions back to bare soil represented a significant part of recovery dynamics. The average transition time from bare soil to regrowth > 2 m was 5.2 years and the net annual recovery rate (i.e., recovery corrected for failure) was 5.9%. By 2024, 25% of disturbed area was covered by vegetation taller than 2 m.

Conclusions: Severely disturbed managed forests in Central Europe retain substantial recovery capacity, even under increasingly extreme climatic conditions. However, the predominance of non-vegetated landcover following disturbance may lead to structurally uniform forests with reduced resilience, suggesting the need for improved management practices.

Several bark and wood-boring insects exhibit eruptive population dynamics during which declining host vigor triggers rapid insect population growth and widespread tree mortality.

The invasive woodwasp Sirex noctilio F. (Hymenoptera: Siricidae) is typically considered a semi-aggressive species due to the absence of aggregation pheromones and a strong dependence on density-independent factors. However, in many parts of its invaded range, S. noctilio displays pronounced outbreaks and spatial aggregation, suggesting more complex population mechanisms.

We hypothesized that S. noctilio behaves as an aggressive forest insect in its invaded range, where population dynamics are driven by a combination of both density-independent (host condition) and density-dependent (population density) mechanisms. To test this, we conducted a field experiment in an invaded region, where host susceptibility was manipulated using herbicide-induced stress, and local population density was assessed by selecting plantations with contrasting wasp densities. We jointly investigated the effects of these factors on female host selection and offspring performance.

We found that host stress strongly influenced female host selection, whereas local population density had little influence on the probability of attack. In contrast, larval performance was largely unaffected by host stress but exhibited positive density-dependent effects, with more and larger individuals emerging from trees in plantations with higher S. noctilio population densities. These positive density-dependent responses are inherently destabilizing and likely contribute to the pattern of eruptive population dynamics seen in invasive populations of this forest insect.

The theory of biotic resistance states that community diversity promotes resistance to biological invasions. This theory has been widely explored for its ability to explain variation in habitat invasibility to non-native plant species and while the theory holds in some systems, it does not in others. In the case of invasions by herbivorous insects, invasibility could be affected by diversity of plants and/or by diversity of native insects.

While only a few studies have explored biotic resistance to insect invasions, limited evidence suggests that plant diversity can actually have a positive effect on invasibility via creation of niches for herbivorous insects though other studies of insect systems indicate that plant diversity has a negative effect on invasibility by diluting the density of hosts.

Almost nothing is known about how native insect diversity affects resistance to invasions by other insects. Here we analyzed a unique inventory of native and non-native Scolytinae/Platypodinae (bark and ambrosia beetles) across the conterminous USA. We assessed the correlates of geographical variation in numbers of both native and non-native species per 50 × 50 km cell.

We find that native tree diversity generally has positive effects on the richness of native beetle species, while the abundance of non-native hosts promotes richness of non-native beetles. We also observed that the effect of native beetle diversity on non-native Scolytinae/Platypodinae species richness is either lacking or positive. These results indicate fundamental differences between plants and insects in the way native and non-native species interact; while interspecific competition can exert a strong influence on plant invasions, it appears less important for insects. Results thus indicate that the biotic resistance hypothesis does not explain invasion patterns of bark and ambrosia beetles.

Purpose of Review: Forests produce timber, mitigate climate change and provide important habitats; yet their capacity to provide these services under rapid global change is uncertain. “Closer-to-nature” forest management (CNFM) has been proposed by the EU Forest Strategy as a way to reconcile competing demands on forests while enhancing their resilience, but experiences with its implementation remain limited. We synthesized expert knowledge about CNFM in Central Europe, a region with a history of diverse forest management practices that has recently experienced severe impacts of climate change. We used a two-stage Delphi approach (including a questionnaire and a workshop) with experts in forest ecology and management to find a consensus about the effects of specific CNFM tools, and to identify knowledge gaps, barriers, and good practice examples of CNFM.

Recent Findings: A wider implementation of CNFM is likely to benefit biodiversity and ecosystem services under climate change, with only one clear trade-off identified between setting areas aside and wood production. However, limited empirical evidence exists for many of the expected effects. Substantial obstacles hinder the implementation of CNFM, including administrative constraints, social barriers, and gaps in knowledge and education. Nonetheless, we identified numerous successful cases of CNFM implementation from local to national scales in Central Europe.

Summary: CNFM is viewed as a potent strategy to navigate future social and ecological uncertainties, including large-scale disturbances. However, the implementation of CNFM should be adapted to the local context and ensure landscape-scale heterogeneity. Existing good practices could serve as examples for mainstreaming CNFM in Central Europe and beyond.

Central Europe has been a hotspot of forest disturbance during 2018–2020, with large pulses of tree mortality from drought and bark beetles. Post-disturbance recovery is crucial for forest resilience and the continued provision of ecosystem services. We surveyed 849 plots in disturbance hotspots across 10 Central European countries to assess the state of early (3–5 years) post-disturbance tree regeneration.

Our specific objectives were to quantify post-disturbance tree recovery, identify key drivers, and assess future trajectories using model-based analyses. We found robust tree recovery throughout Central Europe, with median stem densities of 4750 n ha−1. Only 7% of plots had no regeneration. Regeneration density increased with precipitation, particularly at warm sites, and decreased with disturbance size.

The most frequently regenerating tree species was Picea abies (present on 48% of plots), a species that is poorly adapted to future heat and drought. Overall, we found that 75% of the currently established trees are projected to be outside of their climatic niche by the end of the century under moderate climate change (RCP4.5). We conclude that while Central European forests recover well from recent disturbances, they lack sufficient post-disturbance reorganization to enable sufficient adaptation to future climate.

Invasive species are spreading globally, threatening ecosystems, biodiversity, agriculture and human health. When efforts to prevent the establishment of invasive species fail and eradication is not possible, containment becomes necessary to slow or stop the spread of established invaders. A major question is, therefore, how to allocate treatments across space and time to contain populations cost-effectively.

Here, we examine how to optimize strategies for slowing the spread of the spongy moth (Lymantria dispar) in North America by utilizing gaps with lower densities of host plants. Around these gaps, managers can apply both bio-pesticides and mating disruption using synthetic pheromones to disrupt male mate-finding. We develop a spatially explicit model of the moth's population dynamics, and we develop a novel algorithm that finds the optimal spatial allocation of the two methods across landscapes with heterogeneous host-plant distributions.

Our results show that combining pesticide application and mating disruption around host-plant gaps significantly improves cost efficiency: Optimal treatment allocates mating disruption to low moth-density regions nearer the moth-free area and pesticides to higher moth-density regions nearer the invasion front, with minimal spatial overlap in treatments.

Synthesis and applications: Containment of invasive species can be made markedly more cost-effective by prioritizing landscape features that naturally impede spread. Targeting treatments around host-plant gaps supports a clear operational rule: use mating disruption where densities are low to prevent establishment and concentrate pesticides where densities are high to suppress the advancing front, avoiding costly overlap. More broadly, the algorithm provides a general framework for computing optimal, landscape-specific containment allocations over space.

The effects of climate change are exacerbating the impact of drought and heat stress on forest ecosystems, affecting forests worldwide. This study investigates the physiological responses of mature Norway spruce (Picea abies) to drought and thermal stress, focusing on sap flow and crown temperature. Three trial plots were established in Kostelec nad Černými Lesy, Czech Republic, under different conditions: forest edge, under rain-excluding roofs (simulating drought), and forest interior.

A combination of remote sensing techniques, including spectral indices, LiDAR, and direct sap flow measurements, was used to assess the tree response. Sap flow sensors, aerial hyperspectral, and thermal imaging were employed to measure sap flow and crown temperature, while LiDAR was used to assess canopy structure. Edge trees exhibited pronounced thermal stress with crown temperatures elevated by 2.91°C (large effect) yet maintained sap flow comparable to controls (negligible effect). Conversely, drought-stressed trees showed substantial reductions in sap flow (−2.14 kg/h, large effect) despite moderate crown temperature increases (+0.70°C, medium effect). Spectral indices decreased significantly in both stressed groups (large effect), proving valuable for detecting water stress.

Bark beetle attacks occurred exclusively in drought-stressed plots. Generalized additive models revealed that sap flow was primarily driven by trunk diameter, soil water potential, and crown temperature, while crown temperature was predominantly controlled by neighborhood canopy density, sap flow, and solar radiation. These findings highlight the importance of understanding physiological responses for developing forest management strategies to mitigate climate change effects and bark beetle outbreaks.

Wildfires, insect outbreaks, and storms cause large pulses of tree mortality. Climate change amplifies these forest disturbances, yet their future magnitude and extent remain uncertain. Here, we simulated future forest disturbance regimes at 100-meter resolution across Europe using a deep learning–based simulation framework.

Our results show that forest disturbances will continue to increase throughout the 21st century, with disturbed areas more than doubling relative to the recent past under an unabated continuation of climate change. Wildfires are the main agent driving future disturbance change. Changing disturbances result in an increase in young forests, substantially altering Europe’s forest demography. Because of their profound implications for forest carbon storage and the habitat value of forest ecosystems, disturbances should be a priority of forest policy and management.

Understanding ecosystem function and dynamics is essential for crafting effective, long-term forest management strategies. Our study integrates chronosequence data, ecosystem modeling using Biome-BGCMuSo, and eddy covariance flux tower measurements to test the hypothesis that Net Ecosystem Productivity (NEP) reaches its maximum at a similar relative age across different forest types. We focused on contrasting biomes consisting of Northern Hardwoods, Douglas Fir, Jack Pine, Black Spruce and Southeastern hardwoods.

Our results indicate broadly consistent NEP maximization across forest systems examined, with ecosystem modeling producing peak NEP at a relative stand age (ratio of stand age to site-specific longevity) of 0.24–0.39 and a transition to near-zero NEP between 0.46–0.86. This pattern aligns with Odum's conceptual model of ecosystem development, reflecting shifts in photosynthetic gains and respiratory losses as stands mature. Analysis combining chronosequence observations, process-based ecosystem model outputs, and eddy covariance measurements shows that NEP peaks at similar relative ages across forest types, a pattern that cannot be identified using a single approach in isolation. Sensitivity analyses under future climate change scenarios suggest that these patterns are robust to the tested range of environmental conditions.

By synthesizing empirical data and process-based modeling, this analysis addresses limitations of traditional chronosequence studies, enhancing our ability to project net carbon sequestration across the complete lifespan of a stand. Our research provides model based quantitative evidence consistent with established ecological theories of forest carbon dynamics and contributes to the debate on forest carbon permanence and trade-offs in near-term climate mitigation strategies, such as harvest deferrals and stand re-establishment.

The high productivity of forests planted with non-native tree species is partly dependent on enemy release, a benefit that may erode as specialist herbivores accumulate over time. The accidental introduction of co-evolved insect herbivores from the native range of the planted tree can thus have severe ecological and economic consequences. Anticipating these risks requires identifying not only which pests can establish and cause damage, but also where damaging outbreaks might occur.

Here, we used historical pest damage data from North America to model the climatic suitability for pest damage to Douglas-fir (Pseudotsuga menziesii) where it is utilized in plantation forestry in other world regions. We focused on the three most damaging pests of Douglas-fir in its native range: Douglas-fir beetle (Dendroctonus pseudotsugae), Douglas-fir tussock moth (Orgyia pseudotsugata), and Western spruce budworm (Choristoneura freemani).

Results show that climatic factors strongly constrain potential establishment of Douglas-fir and other host trees of these pest species, whereas climatic suitability for damage exhibits weaker and species-specific patterns. In two regions where most Douglas-fir is planted outside its native range, Europe and New Zealand, currently planted areas are broadly climatically unsuitable for damaging pest outbreaks. These findings highlight the importance of assessing the climatic niche of pest damage rather than simply modeling the niche of pest establishment when assessing pest invasion risk and provides a framework to inform proactive biosecurity and forest management strategies.

Broadleaf-feeding bark beetles remain far less studied than conifer-infesting species, particularly with respect to their semiochemical orientation and host selection. Here, we investigated the responses of the beech bark beetle Taphrorychus bicolor to host- and non-host-derived volatile organic compounds (VOCs) using field trapping experiments and electrophysiological analyses conducted in the Voděradské bučiny National Nature Reserve (central Bohemia, Czech Republic).

Pheromone-baited traps were supplemented with plant material from the host Fagus sylvatica or the non-host species Picea abies and Taxus baccata, and relative trap catches and male proportions were evaluated using generalized linear mixed-effects models. Traps baited with pheromone alone captured the highest number of T. bicolor (122,342 individuals), whereas the addition of P. abies branches significantly reduced trap catches and resulted in the lowest proportion of males (14%) among all treatments, suggesting a potential repellent effect of spruce-derived cues. Branches of F. sylvatica and T. baccata did not significantly affect beetle captures compared with the pheromone-only control, indicating the absence of an attractive effect of host-derived volatiles under the experimental conditions used.

VOCs emitted by host beech and non-host spruce were collected using dynamic headspace sampling and analyzed by GC–EAD and GC×GC–TOF–MS. Antennal responses in beech samples were elicited by eucalyptol, γ-terpinene, and terpinolene, whereas in spruce samples two unidentified compounds elicited antennal responses, with host identity explaining 41.2% of the variation in antennal response profiles (R² = 0.412, p < 0.001). No antennal responses were detected to abundant monoterpenes in either VOC blend. This study provides the first evidence of differential antennal responses to host- and non-host-derived VOCs in T. bicolor, together with behavioral evidence of a potential repellent effect of non-host volatiles, with implications for mixed forest management strategies aimed at reducing bark beetle pressure on beech stands under ongoing climate change.