Biscogniauxia mediterranea is an opportunistic fungal pathogen associated with charcoal canker disease in both juvenile and mature oak trees. This study investigated the genetic diversity, population structure, and pathogenic variability of B. mediterranea populations in the Zagros forests of Iran using inter-simple sequence repeat (ISSR) markers, with the goal of supporting effective forest disease management strategies. A total of 159 isolates were obtained from symptomatic oak trees in four ecologically distinct provinces: Fars, Ilam, Kermanshah, and Kohgiluyeh & Boyer-Ahmad. Genetic analyses revealed high genetic diversity and clear geographic structuring. Most genetic variation occurred within populations, while significant differentiation among regions was detected. Population structure analyses indicated the presence of major genetic groups associated with geographic origin, with additional overlapping patterns suggesting gene flow among regions. Pathogenicity tests confirmed that all tested haplotypes were capable of causing charcoal canker, with isolates from western regions exhibiting greater aggressiveness than those from the southwest. Overall, the findings indicate that geographic and environmental factors are associated with variation in both the population structure and pathogenic potential of B. mediterranea, providing guidance for targeted management of oak decline in the Zagros forests.

ABSTRACT Over recent decades, the decline of oak trees, which has emerged as the most significant challenge to the Zagros forests (ZFs), poses serious threats to carbon storage (CS) and economic valuation, jeopardizing the ecological and economic sustainability of this vital ecosystem. This study utilizes remote sensing techniques to evaluate the impact of oak tree decline on CS and its economic value in the ZFs of Kuhdasht, Lorestan Province, Iran. We used Sentinel-2 data (15 June 2021). This study measures in situ forest above-ground biomass (FAGB) by analyzing 224 systematically selected 20 m × 20 m plots and recording the average crown diameter (ACD) of each tree. We employed multivariate linear regression (MLR), artificial neural networks (ANN), and K-nearest neighbors (KNN) to model FAGB. Next, we used 50% of the AGB map value to calculate the CS map. Subsequently, we considered 3.66 t of carbon dioxide (CO2) for each CS ton. Additionally, we calculated the economic value of CS using an average rate of €49/t of CO2 sequestered. Results indicate that MLR based on the normalized difference vegetation index (NDVI) (R 2 = 0.73, rRMSE = 21.88) was the most effective model for the area studied. Moreover, Sentinel-2 imagery proved highly efficient in estimating FAGB in the degraded zones of ZFs. The economic valuation estimates the value of carbon absorption at €53 million for a healthy forest and €37 million for a severely declining one. The study found that as forest decline increases, its economic value decreases, with the highest values in healthy areas and the lowest in the most declining regions.

ABSTRACTAcute oak decline (AOD) is a complex disease of oak trees (Quercus spp.) which results in bleeding stem cankers and potential tree mortality. A polymicrobial complex is implicated in causing AOD, of which the most commonly isolated species are Brenneria goodwinii and Gibbsiella quercinecans. Bacteriophages (phages), natural predators of bacteria, can act as biocontrol agents that reduce bacterial infections in trees. In this study, the first phages that lyse B. goodwinii and G. quercinecans, BREN6 and GIB1 phages respectively, were isolated from AOD‐impacted trees. Genomic analyses and transmission electron microscopy showed that BREN6 is a novel phage type with siphovirus morphology, whereas GIB1 possesses characteristics typical of N4‐like phages. While in vitro assays showed that each phage could effectively reduce their hosts' population growth for at least 24 h, application of the phages to either single or dual species communities of B. goodwinii and G. quercinecans in the stems of oak saplings showed that the phages had a minimal impact on their host populations, and in some trees actually resulted in higher bacterial populations. Our data show that the application of these phages does not alter the in planta population dynamics between B. goodwinii and G. quercinecans, and emphasises the importance of assessing phage effectiveness within natural settings.

Drought–competition synergy drives cork oak (Quercus suber) decline: multi-proxy evidence from semi-arid Algerian forests

The scientific event “Italian Oak Forests Facing Stress Factors and Climate Change: Current Evidence, Ecophysiological Knowledge and Management Perspectives”, organized by the Italian Society of Silviculture and Forest Ecology (SISEF) and the Italian Academy of Forest Sciences, addressed the critical issues threatening the conservation of oak forests in Italy. Oak decline, documented since the 1980s, emerges as a multifactorial phenomenon driven by climatic stress (drought, heatwaves), biotic agents (pathogens, insects), and species-specific ecophysiological traits. A meta-analysis of over 200 studies shows drought reduces vigor and resilience but triggers adaptive mechanisms such as stomatal regulation and osmotic adjustment. Future scenarios predict a reduction in forest cover and the replacement of native species with more resistant species to extreme climatic events. Long-term data from the CONtrollo degli ECOsistemi FORestali (CONECOFOR) program confirm species-specific strategies: Q. pubescens sheds leaves in summer, Q. cerris exhibits sudden mortality, while Q. ilex, though drought-tolerant, is vulnerable to extreme events. Regional case studies (Sardinia, Apulia, Lombardia-Ticino Park) highlight widespread dieback and mortality in oak stands and the role of pathogens such as Phytophthora spp. and Diplodia corticola in exacerbating the negative impact of extreme drought events. Sustainable management should enhance genetic diversity and select resilient genotypes, integrating either ground and remote sensing monitoring. The concluding roundtable proposed establishing a National Technical Board to coordinate monitoring, training, and adaptive strategies, aligned with the National Forest Strategy. This body should ensure multidisciplinarity, stakeholder representation, and operational capacity, leveraging national, regional, and EU resources to counter the growing risk of resilience loss in Italian oak forests.

The Muški bunar old-growth forest on Mount Psunj represents one of the rare preserved mixed ecosystems of sessile oak (Quercus petraea (Matt.) Liebl.) and European beech (Fagus sylvatica L.) in Southeastern Europe, providing an important reference for understanding natural forest dynamics. This study aimed to analyse stand structure, age distribution, growth dynamics, and disturbance regime based on repeated field surveys conducted in 1979 and 2021. The results revealed pronounced structural heterogeneity and clear interspecific differences. European beech dominates smaller- and medium-diameter classes, as well as a wider range of age classes, whereas sessile oak is primarily present in older and larger diameter classes. A very high growing stock (1155.81 m3 ha−1) indicates exceptional stand productivity, with maximum cambial ages of 295 years for oak and 253 years for beech. Basal area increment analysis showed that both species maintain substantial growth at advanced ages. However, recent decades show divergence, with increasing growth in beech and stagnation or decline in oak. Importantly, growth releases in sessile oak were not accompanied by successful regeneration, indicating a decoupling between growth response and recruitment. Stand dynamics are mainly driven by low-intensity disturbances. These findings highlight the importance of old-growth forests as reference systems and improve understanding of species-specific responses to disturbance.

Mediterranean cork oak forests provide essential ecosystem services but face increasing threats from climate change, ecosystem simplification, and oak decline. Ensuring their long-term sustainability requires governance approaches that integrate regional planning frameworks with international certification standards. This study presents a pioneering case of public cork oak forest management in Alà dei Sardi, Sardinia (Italy), where municipal forest planning was aligned with national and regional regulations and further enhanced through Forest Stewardship Council® (FSC®) certification. The FSC system offers internationally recognized standards and the Ecosystem Services Procedure (FSC-PRO-30-006 v2-1) to verify responsible forest management and quantify key ecosystem benefits. The Alà dei Sardi forest is the first publicly owned municipal cork oak forest to achieve FSC Forest Management certification, with demonstrated positive impacts of its management activities on biodiversity conservation, carbon sequestration and storage, water protection, soil conservation, and recreational services. The certification process integrated management planning, stakeholder engagement, monitoring, and adaptive interventions, showing that public institutions can combine legal frameworks with voluntary standards to enhance ecological performance, accountability, and socio-economic value. This case illustrates a potentially scalable and replicable model for sustainable forest governance, linking territorial planning with market-based mechanisms, and provides a practical example of governance for resilient and multifunctional forest systems.

Agricultural crop productivity and global forest biomes are coming under increasing threat from insect pests and microbial pathogens. This impact is worsened by inter-kingdom insect-microbe interactions that can increase transmission and disease severity in affected plants. While bacterial chemical cues have been shown to directly influence insect behaviour, the impact of insect-derived compounds on phytopathogens is poorly understood. Here, we investigated the chemical basis for interactions between beetle larvae and bacteria in acute oak decline (AOD), a disease characterized by inner bark necrosis of Quercus robur and Q. petraea involving a polymicrobial consortium, including Brenneria goodwinii and larval galleries of Agrilus biguttatus. We found that A. biguttatus larval extractable metabolites increase bacterial growth rate and final cell density during in vitro culture, and stimulate the differential expression of ∼600 genes, including the type III secretion system and its effectors, which are major virulence factors in plant pathogens. Chemical compounds from closely related insect species did not have this effect. These findings highlight the importance of inter-kingdom interactions in plant disease and suggest a role for insect-derived chemical elicitors in facilitating the virulence of phytopathogens.

Abstract Climate aridification and the increasing incidence of exotic pests and pathogens are contributing to a concerning global rise in tree decline and mortality. The analysis of tree elemental composition (the elementome) offers a promising tool to detect physiological disruptions and identify early‐warning signals of decline. However, the role of elemental alterations—particularly in response to exotic pathogens—remains underexplored. Here we analysed the elemental signature of tree decline in Mediterranean savanna‐type ecosystems (dehesas) invaded by the aggressive exotic soil‐borne pathogen Phytophthora cinnamomi . Using a multi‐scale approach (regional and local), we assessed root elemental concentrations and stoichiometry in relation to crown defoliation, soil physicochemical properties and P. cinnamomi abundance in 500 adult Quercus rotundifolia trees across 30 sites in Southern Spain. Our results revealed a distinct chemical signature of tree decline in the root elementome, with patterns varying across spatial scales. At the regional scale, only sodium (Na) emerged as an indicator of site‐level decline. In contrast, the local scale revealed strong and consistent chemical alterations in symptomatic trees, including elevated calcium (Ca) concentrations and reduced levels of key nutrients (potassium [K], phosphorus [P], iron [Fe], zinc [Zn]) and elemental ratios (K:Ca) compared to asymptomatic neighbours. Among all variables, the K:Ca ratio was the best discriminator between asymptomatic and symptomatic trees, showing significant associations with crown defoliation and P. cinnamomi abundance. Elevated Ca uptake in symptomatic trees may reflect a defensive response to pathogen infection but also contribute to nutritional imbalances that exacerbate decline. Synthesis . Our findings highlight the value of multi‐scale elementome analysis for identifying sites and trees vulnerable to decline. Specifically, we showed that nutritional imbalances (particularly the K:Ca ratio) can act as reliable early‐warning signals of pathogen‐driven decline in Mediterranean systems, enabling rapid management responses. We advocate further research on plant elementomes across diverse pathosystems to uncover broader patterns that could inform biosecurity programs aimed at mitigating the growing impacts of exotic pathogens worldwide.

Mediterranean agroforestry systems (AFSs), typified by the Iberian Dehesas and Portuguese Montados, are multifunctional landscapes where Quercus species act as ecological keystones sustaining biodiversity, soil fertility, and rural livelihoods. These systems are increasingly affected by complex oak decline syndromes driven by drought, soil degradation, and climate-induced pathogen outbreaks. Conventional chemical controls are often ineffective and environmentally detrimental, underscoring the need for ecologically sound management alternatives. This review synthesizes recent advances in the application of microbial biological control agents (MBCAs) to manage diseases in Mediterranean Quercus species, including Q. ilex, Q. suber, Q. faginea, and Q. pyrenaica. We conducted a structured literature review using predefined keyword searches in Web of Science and Scopus, followed by the screening of records to identify 22 relevant peer-reviewed studies on microbial disease control in Mediterranean Quercus species. We identified 20 peer-reviewed studies that reported that MBCAs—primarily from Bacillus, Serratia, Streptomyces, Trichoderma, Simplicillium and Alternaria—exert biocontrol effects through antibiosis, mycoparasitism, competition for ecological niches, and the induction of host defense responses. Although most experiments were conducted in vitro, some demonstrated significant disease suppression in seedlings infected by Phytophthora cinnamomi, Diplodia corticola, and Biscogniauxia mediterranea. Future research should integrate field-based validation and microbiome-oriented forest management approaches to enable the operational use of microbial-based disease control strategies in AFS landscapes.

Global forest biomes face increasing stressors and disease outbreaks that threaten ecosystem health. Tree-associated microbiota are vital for tree resilience, yet their responses to biotic and abiotic stressors in mature trees remain poorly understood. Using an experimental woodland plot of 144 Quercus petraea trees subjected to drought (rain exclusion), nutrient stress (ringbarking), and biotic treatments (bacterial pathogens and beetle larvae) to simulate acute oak decline, we tracked microbial communities in leaf, stem, and root/rhizosphere tissues across four time points over 2 years. Oak trees hosted distinct microbial communities across tissue types, which remained largely stable under stress. Rain exclusion significantly altered microbiota composition, though these changes explained less than 1% of total variance. Actinobacteriota, linked to drought tolerance, increased in the root/rhizosphere of rain-excluded trees. These findings reveal a surprising resilience of oak-associated microbial communities to environmental and biotic disturbances, highlighting their potential role in forest ecosystem stability.

Amid the ongoing decline of oak forests across Europe, implementing measures to detect, monitor, and prevent infestations by defoliating insect species has become increasingly urgent. Among these species, Lymantria dispar (Linnaeus, 1758) represents one of the most significant threats to oak forests. Adhesive panel traps baited with pheromone lures are commonly used for monitoring, but their non-selective nature leads to unintended captures of non-target insects, including Coleoptera. This study was conducted during the 2023 flight season (June-August) in two outbreak-affected oak stands in southern Romania (Baba Ana and Tatina). Twelve atraDISPAR-baited sticky panels were installed per sample plot, arranged in three replicates of four panels each in a square layout. A total of 1,844 beetles from 21 non-target beetle species belonging to 11 families were collected and classified by feeding preference. Agrilus angustulus (Illiger, 1803) (Buprestidae), one of the species associated with oak decline in Western Europe, was the most abundant among the species identified. Species richness was comparable (13 in Tatina, 12 in Baba Ana), but abundance varied greatly (139 specimens in Tatina vs. 1,705 in Baba Ana). The observed attraction of several secondary pest beetles suggests that adhesive panel traps may serve not only in L. dispar monitoring but also as a potential tool for assessing broader forest health.

The oak decline experienced in recent decades resulted in structural changes of the shrub community. The goal of this research was to determine the size condition on high shrubs (> 1.0 m in height) and to compare the average parameters of species in each sample site in 2022. The following measurements were performed in four plots: height, shoot diameter, and foliage cover. 6–9 native high shrub species were observed in the understory plots. The mean height and shoot diameter distribution of high shrubs varied between 1.22 and 10.18 m and between 0.84 and 11.88 cm respectively. The mean foliage cover of high shrub species changed between 0.11 and 15.26 m2 in the vegetation period. One-way ANOVA indicated a non-significant difference (p > 0.05) among high shrub species’ size conditions on sample plots. Our results suggest that the size characteristics of the shrubs were similar on the plots, and it is worth investigating the relationship between shoot height and shoot diameter in more detail.

ABSTRACT This study presents the first confirmed occurrence of Rahnella victoriana in symptomatic pedunculate oaks ( Quercus robur ) in Poland. Surveys were conducted in the Odra River valley, where 14.6% of examined trees exhibited symptoms similar to those of Acute Oak Decline (AOD). Bacterial isolation and 16S rRNA sequencing identified Brenneria goodwinii , Gibbsiella quercinecans , and R. victoriana among symptomatic trees. Pathogenicity tests confirmed that R. victoriana could induce necrosis under controlled conditions, and the bacterium was re‐isolated from infected tissues. These findings expand the known distribution of R. victoriana in Europe and highlight its possible role in the AOD pathobiome.

Drought-induced tree mortality and dieback is expected to become an increasingly significant issue as climate change increases the frequency, severity and duration of droughts. The primary proposed mechanism of drought-induced decline is hydraulic failure, which is mechanistically linked to xylem architecture. However, annual variation of xylem anatomical traits has largely been overlooked as a possible driver of tree decline, with a focus instead on traditional ring-width based dendrochronological methods. Here, we employ a quantitative wood anatomy approach to examine whether differences in xylem vessel lumen area were related to decline risk during a recent drought-induced decline of chestnut oak (Quercus prinus) from Southern Indiana, USA. Our results show that over at least the past 60years, healthy trees built consistently wider vessels than those that succumbed. This phenomenon has now been observed across three continents, and in both tracheid- and vessel-bearing species, indicating that conduit size may be related to drought survival, likely as an indicator of long-term stress. Moreover, an analysis of the sensitivity of vessel lumen area to climate variables suggests that early winter warming may promote the production of wider vessels in the following year. In contrast, a negative correlation between prior year growing season length and vessel lumen area suggests that extended growing seasons may lead to narrower, potentially more vulnerable xylem vessels. These effects were less pronounced in the declining trees, hinting that already-stressed trees were less sensitive or physiologically unable to respond to climatic variability. Designing studies aimed at understanding the drivers of intra-specific variation in xylem conduit architecture could improve our ability to predict tree dieback and mortality under future climate scenarios.

The coexistence of natural and planted forests is a significant feature in the Mediterranean and other regions of the world.Understanding this dynamic is crucial for assessing forest management.The purpose of this research is to provide a long-term scientific assessment of forest cover dynamics in the Mamora forest , with the aim of generating new insights into the drivers of cork oak (natural forest) decline and the expansion of plantation forests (Eucalyptus, Pine, Acacia) and bare land.Five Landsat images (1989, 1999, 2009, 2019, 2022) were classified using the Maximum Likelihood Classification (MLC) algorithm, and land cover changes were quantified.Statistical analyzes were conducted using generalized linear mixed models (GLMs).Over the past three decades, natural forest cover declined by -8.15% per decade, while plantation forests and bare land increased by 4.50% and 312.5% per decade, respectively.This research highlights the conversion of Mamora's natural forest into plantation forest and bare land, driven by a blend of natural and human-induced factors.Our findings provide valuable insights for guiding rehabilitation efforts and support sustainable forest management.Furthermore, it is essential to adopt specific strategies, including cork oak restoration, assisted natural regeneration, and improved monitoring of forest resources.Future research should explore the effectiveness of these approaches across different ecological and socio-economic contexts to refine forest policy.

The role of volatile cues in mediating tree host-bacteria-insect interactions in acute oak decline.

Invasive plant pests and pathogens cause substantial environmental and economic damage. Visual inspection remains a central tenet of plant health surveys, but its sensitivity (probability of correctly identifying the presence of a pest) and specificity (probability of correctly identifying the absence of a pest) are not routinely quantified. As knowing sensitivity and specificity of visual inspection is critical for effective contingency planning and outbreak management, we address this deficiency using empirical data and statistical analyses. Twenty-three citizen scientist surveyors assessed up to 175 labelled oak trees for three symptoms of acute oak decline. The same trees were also assessed by an expert who has monitored these individual trees annually for over a decade. The sensitivity and specificity of surveyors was calculated using the expert data as the 'gold-standard' (i.e., assuming perfect sensitivity and specificity). The utility of an approach using Bayesian modelling to estimate the sensitivity and specificity of visual inspection in the absence of a rarely available 'gold-standard' dataset was then examined with simulated plant health survey datasets. There was large variation in sensitivity and specificity between surveyors and between different symptoms, although the sensitivity of detecting a symptom was positively related to the frequency of the symptom on a tree. By leveraging surveyor observations of two symptoms from a minimum of 80 trees on two sites, with reliable prior knowledge of sites with a higher (~0.6) and lower (~0.3) true disease prevalence we show that sensitivity and specificity can be estimated without 'gold-standard' data using Bayesian modelling. We highlight that sensitivity and specificity will depend on the symptoms of a pest or disease, the individual surveyor, and the survey protocol. This has consequences for how surveys are designed to detect and monitor outbreaks, as well as the interpretation of survey data that is used to inform outbreak management.

Extreme heat waves coupled with severe drought episodes are increasing in frequency in the Mediterranean region. Such climatic events pose significant threats to evergreen sclerophyllous vegetation, despite their inherent resistance and adaptation to drought conditions. Over recent decades, several cases of dieback affecting Quercus ilex, Quercus suber, and other evergreen shrubs have been reported across the Mediterranean basin. In Italy, the first reports of Q. ilex dieback due to climatic events date back to 2012 in Tuscany, and with more extensive impacts observed following the extreme drought of 2017. During the summer of 2024, widespread dieback phenomena were reported across Southern Italian regions, including Apulia, Basilicata, and the islands of Sardinia and Sicily. The symptoms were consistent and recurrent in all the affected areas, characterized by partial or total foliar browning, followed by wilting and branch dieback. Notably, resprouting from dormant buds was observed in affected branches and leaves in the following rainy season. Affected areas showed ongoing symptoms of oak decline, often associated with the presence of Phytophthora spp. and other opportunistic pathogens, suggesting a complex interaction between biotic and abiotic stressors. This study aims to document and analyze the most relevant cases of Q. ilex dieback occurring in central and southern Italy, using also data collected through the SilvaCuore web application. The phenomenon of dieback and mortality of Q. ilex is still poorly understood in terms of the cause-and-effect relationships, the relative contribution of biotic and abiotic factors, the extension and severity of damage, and the ecological consequences. Although Mediterranean woodlands (forests and shrublands) are scarcely represented in the current scientific and monitoring programs (ICP Forests Level I network), the available results show an increase in dieback and mortality in Italy since 2012. We emphasize the urgent need for coordinated research efforts to study and map this phenomenon. Proposed actions include establishing a network of permanent monitoring plots that combine phytopathological and ecophysiological assessments over time, deploying comprehensive terrestrial and remote sensing monitoring techniques, and involving citizens in early detection efforts. Finally, the research should aim to identify the site-specific and management-related factors that have contributed to the extent and intensity of the dieback phenomenon. Understanding these drivers is critical for developing effective management strategies aimed at mitigating the impacts of these dieback events and enhancing the resilience of the most vulnerable forest stands.

We monitored the decline of three oak species, including Quercus brantii , Q. infectoria , and Q. libani , in the Northern Zagros forests of Iran over four years (2019–2022) to identify temporal variation in decline severity and to investigate key environmental and stand structural drivers. Our monitoring across eight sites showed species-specific decline variation, with Q. libani facing the most severe decline, followed by Q. infectoria and Q. brantii . Healthy tree percentages significantly decreased, with increases in decline stages and dead trees. Species-specific physiological and ecological traits influenced vulnerability to environmental stressors. Quercus libani , which typically occurs at higher elevations, was disproportionately affected by reduced precipitation and increased evaporation due to rising elevation. A strong negative correlation between elevation and precipitation (r = − 0.65), combined with increased solar radiation and wind exposure at higher altitudes, highlighted drier conditions and higher evaporative demand at these sites. Meteorological factors, particularly temperature, precipitation, and evaporation, played a critical role in the decline of oak trees, with warmer years exacerbating water stress and heat intensification, ultimately contributing to increased tree mortality. Additionally, the results revealed that six out of eight sites with grazing experienced above-average decline rates, indicating a strong correlation between land-use type and oak decline severity. Throughout the study, shoot-originated trees showed consistent health decline across sites, whereas seed-originated trees displayed variable trends. These findings highlight the need for targeted, adaptive management strategies in the Northern Zagros, including species-specific interventions, climate-adapted regeneration practices, reduced-impact land-use, and ongoing monitoring to mitigate oak decline. • Healthy trees declined significantly from 2019 to 2022, with rising mortality rates. • Higher elevations faced drier conditions, severely impacting Quercus libani . • Shoot trees decline consistently; seed trees varied by site and year. • Climate factors like temperature and evaporation worsened oak water stress. • Human activities strongly affected oak health; sustainable practices are crucial.