Mediterranean Forest Research Articles

Impact of meteorological conditions on the biogenic volatile organic compound (BVOC) emission rate from eastern Mediterranean vegetation under drought

Abstract. A comprehensive characterization of drought's impact on biogenic volatile organic compound (BVOC) emissions is essential for understanding atmospheric chemistry under global climate change, with implications for both air quality and climate model simulation. Currently, the effects of drought on BVOC emissions are not well characterized. Our study aims to test (i) whether instantaneous changes in meteorological conditions can serve as a better proxy for drought-related changes in BVOC emissions compared to the absolute values of the meteorological parameters, as indicated by previous BVOC mixing-ratio measurements and (ii) the impact of a plant under drought stress receiving a small amount of precipitation on BVOC emission rate, and on the manner in which the emission rate is influenced by meteorological parameters. To address these objectives, we conducted our study during the warm and dry summer conditions of the eastern Mediterranean region, focusing on the impact of drought on BVOC emissions from natural vegetation. Specifically, we conducted branch-enclosure sampling measurements in Ramat Hanadiv Nature Park, under natural drought and after irrigation (equivalent to 5.5–7 mm precipitation) for six selected branches of Phillyrea latifolia, the highest BVOC emitter in this park, in September–October 2020. The samplings were followed by gas chromatography–mass spectrometry analysis for BVOC identification and flux quantification. The results corroborate the finding that instantaneous changes in meteorological parameters, particularly relative humidity (RH), offer the most accurate proxy for BVOC emission rates under drought compared to the absolute values of either temperature (T) or RH. However, after irrigation, the correlation of the detected BVOC emission rate with the instantaneous changes in RH became significantly more moderate or even reversed. Our findings highlight that under drought, the instantaneous changes in RH and to a lesser extent in T are the best proxy for the emission rate of monoterpenes (MTs) and sesquiterpenes (SQTs), whereas under moderate drought conditions, T or RH serves as the best proxy for MT and SQT emission rate, respectively. In addition, the detected emission rates of MTs and SQTs increased by 150 % and 545 %, respectively, after a small amount of irrigation.

Classification and Mapping of Fuels in Mediterranean Forest Landscapes Using a UAV-LiDAR System and Integration Possibilities with Handheld Mobile Laser Scanner Systems

In this study, we evaluated the capability of an unmanned aerial vehicle with a LiDAR sensor (UAV-LiDAR) to classify and map fuel types based on the Prometheus classification in Mediterranean environments. UAV data were collected across 73 forest plots located in NE of Spain. Furthermore, data collected from a handheld mobile laser scanner system (HMLS) in 43 out of the 73 plots were used to assess the extent of improvement in fuel identification resulting from the fusion of UAV and HMLS data. UAV three-dimensional point clouds (average density: 452 points/m2) allowed the generation of LiDAR metrics and indices related to vegetation structure. Additionally, voxels of 5 cm3 derived from HMLS three-dimensional point clouds (average density: 63,148 points/m2) facilitated the calculation of fuel volume at each Prometheus fuel type height stratum (0.60, 2, and 4 m). Two different models based on three machine learning techniques (Random Forest, Linear Support Vector Machine, and Radial Support Vector Machine) were employed to classify the fuel types: one including only UAV variables and the other incorporating HMLS volume data. The most relevant UAV variables introduced into the classification models, according to Dunn’s test, were the 99th and 10th percentile of the vegetation heights, the standard deviation of the heights, the total returns above 4 m, and the LiDAR Height Diversity Index (LHDI). The best classification using only UAV data was achieved with Random Forest (overall accuracy = 81.28%), with confusion mainly found between similar shrub and tree fuel types. The integration of fuel volume from HMLS data yielded a substantial improvement, especially in Random Forest (overall accuracy = 95.05%). The mapping of the UAV model correctly estimated the fuel types in the total area of 55 plots and at least part of the area of 59 plots. These results confirm that UAV-LiDAR systems are valid and operational tools for forest fuel classification and mapping and show how fusion with HMLS data refines the identification of fuel types, contributing to more effective management of forest ecosystems.

Deciduous fruit trees and grapevines as alternative crops in Demathophora necatrix (syn. Rosellinia necatrix) infested soils

White root rot, caused by Dematophora necatrix (syn. Rosellinia necatrix), affects deciduous trees. A D. necatrix infection-distribution survey found widespread disease in apple and cherry orchards in northern Israel bordering a Mediterranean forest, although the forest trees were unaffected. Because cherry and apple orchards must be abandoned due to long fungal survival in infested soils, alternative deciduous fruit trees and grapevines were assessed for growth in these D. necatrix-infested orchards. In the field, grapevine rootstocks and the almond–peach rootstock GF-677 were most tolerant to D. necatrix-infested soil. Apple was the most sensitive crop, with the rootstock Hashabi being more tolerant than PI80 or MM104. The Mediterranean forest tree Pistacia atlantica, which can serve as a rootstock for pistachio, was as sensitive as kiwifruit and apple, and persimmon rootstock sensitivity was not different from grapevine. Those results show that beside the above mentioned crops, vineyards can also replace apple orchards in D. necatrix-infested soils and so broadens the list of possible crops for the local farmers in a Mediterranean climate at altitudes above 440 m above sea level. This has also been observed in a commercial 10-year-old vineyard of ‘Shiraz’ grapevines grafted on SO4 rootstock. The almond-peach rootstock GF-677 can also be grown in infested soil, but in commercial orchards requires additional treatment for adequate disease control.

Soil response in a Mediterranean forest ecosystem of Southeast Spain following early prescribed burning

The escalation of global warming, high temperatures, and wildfire frequency in dry ecosystems, including semi-arid landscapes, has resulted in increased wildfire regimes, compromising ecosystem resistance and resilience. To mitigate these risks, prescribed burning (PB) is being employed as a preventive measure to modify fuel loads in forest ecosystems. However, fire can also impact soil structure and microbiota, which play critical roles in nutrient cycling, biodiversity conservation, and overall ecosystem functioning. Therefore, understanding post-fire processes is essential for sustainable forest management. However, while previous studies have explored the effects of prescribed fire management on semi-arid soil properties in Mediterranean forest ecosystems, gaps remain in our understanding of its specific impact on the physical structure, chemical composition, and biological activities of soils.In this study, we conducted early spring PB in SE Spain in 2021 and assessed the ecological and temporal effects of PB on semi-arid soils. Soil respiration (SR) measurements using automatic CO2 flow chambers were employed to evaluate microbiota recovery. To examine impacts on soil structure we evaluated physicochemical characteristics, soil hydraulic conductivity (SHC), and soil water repellency (SWR). No significant differences were observed in any of the variables studied after one year. However, immediate effects were detected shortly after the PB. Our research specifically targeted soil structure and microbiota in a semi-arid landscape with poor soils, characterized by slower recovery and potentially fragile ecosystems. These results provide valuable insights for forest management practices, indicating that prescribed fire management strategies in similar ecosystems are unlikely to cause adverse effects on soil health. However, further research is warranted to explore the potential effects of prescribed fire intensity and seasonality. Future studies can focus on investigating these factors to provide more targeted recommendations for effective forest management strategies and wildfire prevention efforts.

Tackling the Thorny Dilemma of Mapping Southeastern Sicily's Coastal Archaeology Beneath Dense Mediterranean Vegetation: A Drone‐Based LiDAR Approach

Tackling the Thorny Dilemma of Mapping Southeastern Sicily's Coastal Archaeology Beneath Dense Mediterranean Vegetation: A Drone‐Based LiDAR Approach

Thinning followed by slash burning enhances growth and reduces vulnerability to drought for Pinus nigra.

Increasingly frequent severe drought events are pushing Mediterranean forests to unprecedented responses. Lack of management leads to dense forests that are highly susceptible to drought stress, potentially resulting in extensive dieback and increased vulnerability to other disturbances. Forest treatments like thinning and slash burning reduce competition for resources and have the potential to enhance tree growth and vigor and minimize tree vulnerability to drought. Here, we used tree rings to study the growth and physiological response of black pine (Pinus nigra) to drought in northeastern Spain under different treatments, including two thinning intensities (light and heavy, with 10% and 40% basal area reduction, respectively) followed by two understory treatments (clearing alone and in combination with slash burning), resulting in a research design of four treatments plus an untreated control with three replicates. Specifically, we studied basal area increment (BAI), resilience indices, and intrinsic water use efficiency (iWUE) using carbon and oxygen isotope composition (δ13C and δ18O in tree-ring cellulose) before and after treatments. Our results showed that BAI and resistance to drought increased in the heavy-thin (burned and unburned) and light-thin burned units. Resilience increased in the burned units regardless of the thinning intensity, while recovery was not affected by treatment. Slash burning additionally increased BAI in the light-thin and resistance and resilience in the heavy-thin units compared with clearing alone. The stable isotope analysis revealed a minor effect of treatments on δ13C and δ18O. No change in iWUE among treatments was presumably linked to a proportional increase in both net CO2 assimilation and stomatal conductance, which particularly increased in the heavy-thin (burned and unburned) and light-thin burned units, indicating that these trees were the least affected by drought. This study shows that management approaches aimed at reducing wildfire hazard can also increase the vigor of dominant trees under drought stress. By reducing competition both from the overstory and the understory, thinning followed by clearing alone or in combination with slash burning promotes tree growth and vigor and increases its resistance and resilience to drought.

Enhancing Burned Area Mapping Accuracy: Integrating Multi-temporal PCA with NDVI Analysis

Forested lands in the west coast of Turkey, with their similarity to Mediterranean forests, are often found to be highly susceptible to wildfires, necessitating the development of a forest management program to refine and quantify forest fires and their impacts on the environment. In light of this fact, a multi-temporal approach combining Principal Component Analysis (PCA) and Normalized Difference Vegetation Index (NDVI) analysis derived from Sentinel-2 imagery is suggested in the current study. Through PCA of carefully selected bands of Sentinel-2, both recent and historic fire impacts are attempted to be captured. It was found that the first two principal components (PC1 and PC2) predominantly describe landscape characteristics, while the third and fourth components (PC3 and PC4) have high abilities in detecting burn scars. It is worth noting that an increase in the ability to detect burn scars was observed with the inclusion of NDVI and its difference in time (dNDVI) within the PCA process. A high effectiveness level in distinguishing burnt areas from unburnt landscapes was presented by the multi-temporal PCA approach, particularly with dNDVI integration. PC2 and PC3, especially with dNDVI integration, are found to be strong indicative factors of burnt areas. In the classification result, accuracies of different years of fire events differed, and a high accuracy of 98.76% was found in the last fire event year of 2019. However, slight underestimation and overestimation were also observed in older fire scars. Mean accuracy, on average, for the PCA-dNDVI method was found to be higher than that of the MLC method. Furthermore, significant vegetation losses by fire, particularly by the 2019 fire incident, were realized through NDVI assessment. Although it worked well in recent fire scars, overestimating the extent in the case of burned areas from previous years was observed. The potential of multi-temporal PCA integration with NDVI for analysis in mapping burned areas at different scales in fire-prone ecosystems in western Turkey is underlined by the results of this work. Much more successful forest management and assessment strategies after fires have occurred in these ecosystems are helped to be created by this approach. Moreover, the approach is suggested to be one of the strong tools for monitoring fire induced damages across many time scales toward better understanding and management of long-term impacts caused by forest fires in the region.

Arachnid Assemblage Composition Diverge between South- and North-Facing Slopes in a Levantine Microgeographic Site

Local microgeographic sites subdivided by sharp ecological and climatic contrasts are important platforms for measuring biodiversity patterns and inferring the possible effect of climatic and ecological variables on species distributions and habitat use. Here, we report results from 24 months (September 2019–August 2021) of continuous pitfall trapping collection in Lower Nahal Keziv, Western Upper Galilee, Israel (“Evolution Canyon” II (hereafter—EC II)). This site receives an average annual rainfall of 784 mm and contains two slopes that differ markedly by solar radiation and plant formation. The first is the south-facing slope (SFS), which is characterized as a semiarid garrigue and open grassland. The second is the contrasting north-facing slope (NFS), which is characterized by a more humid East Mediterranean forest. The slopes are separated by a narrow valley bottom (VB). Analysis of ca. 1750 arachnid specimens, collected from 70 pitfall traps along the slopes and valley, indicates significantly different arachnid assemblages between the NFS and SFS, likely due to the differences in solar radiation that affect plant-cover percentage, which in turn affects the arachnid assemblage composition. In addition to 98 arachnid taxa collected and identified to species and morphospecies level, this study resulted in the discovery of two species new to science, which are described as part of this publication (100 arachnid species and 11 additional taxa that were not identified to species, a total of 111 taxa). Our study, moreover, contributes new ecological data on the spatial and temporal distribution of arachnids, and therefore attests to the importance of year-round sampling in an understudied region. Overall, our study enables a better understanding of arachnid diversity and their distributions and serves as a reference for future research aimed at testing the effect of climate change and other environmental factors that influence arachnid assemblages in natural habitats.

Combinative effects of thinning and prescribed burning on fuel reduction and soil arthropods: A case study in a Mediterranean pine forest.

Wildfire pressure involves today to implement silvicultural practices that provide a good compromise between reducing fire risk and maintaining ecological functioning. Thinning reduces tree density and low branches, but results in the deposition of a considerable biomass of woody debris on the ground (up to 4800 g m2 in this study). They can be eliminated by prescribed burning, but this raises questions about the fire intensity that can be generated and the impact on soil fauna. We undertook the monitoring of a thinning and prescribed burning operation, separated and combined, in November 2020, in a Pinus laricio stand prone to fire risk, located in Bavella, Corsica. Fuel load was determined, and temperature measurements in the soil were performed using K-type thermocouples. Soil arthropod populations were monitored using pitfall traps, in particular Collembola, Acari, Aranae, and Coleoptera. The combination of thinning and burning resulted in a fire intensity of 75.8 versus 8.4 kW m-1 for burning alone. Maximum temperature rise measured at -2 cm below the surface was less than 5°C for both treatments. The combination of thinning and burning did not result in higher fire intensity at ground level than burning alone, and the soil showed high insulation capacity. Most of the woody debris that burned was small-diameter, and large-diameter debris remained unconsumed. This burning, performed during a period of low biological activity, had no effect on soil arthropods, and the presence of large debris may have provided refuge areas. Collembola group was the faster to recover, and were followed by cohorts of predators in summer, especially Acari. Our results suggest that a combination of burning and thinning in autumn may be beneficial for fire prevention. However, the decomposition of woody debris in relation to fire risk, and the occurrence of pests after these treatments need to be monitored.

Different drought-tolerance strategies of tree species to cope with increased water stress under climate change in a mixed forest.

Trees' functional strategies to cope with extreme drought are essential under climate change. In a mixed Mediterranean forest, we analyzed the functional strategy in response to drought of four co-occurring species (Pinus pinea, Pinus pinaster, Juniperus oxycedrus, and Quercus ilex) during two years. Specifically, we assessed functional traits related to tree water status, leaf water relations, and gas exchange. Different trait-syndrome metrics and the functional strategies under water stress observed suggested a species drought-tolerance differentiation, with the more anysohidric Q. ilex and J. oxycedrus showing a much higher drought tolerance than the more isohydric P. pinea and P. pinaster. All species recovered from negative leaf turgor reached during peak water stress in summer. Q. ilex and J. oxycedrus kept lower leaf osmotic potentials and lower sensitivity of leaf gas exchange and leaf photochemistry to water stress. In contrast, the pine species exhibited more drought-avoidant and water-conservative strategies, yet this behavior was less effective in mitigating water stress's impact on their physiology. The pine species were the most affected by drought, with prolonged near-zero net photosynthesis during summer. P. pinaster was more isohydric than P. pinea and exhibited a lower capacity to maintain leaf turgor. Physiological processes regulating leaf turgor under drought constitute a key functional strategy involved in the carbon and water-related mechanisms, ultimately inducing mortality under hot drought. The currently observed mortality dynamics for P. pinaster, and to a lower extent in P. pinea, may be exacerbated by loss of functional homeostasis.

Modeling and spatialization of biomass and carbon stock using unmanned Aerial Vehicle Lidar (Lidar-UAV) metrics and forest inventory in cork oak forest of Maamora

Recently, the concerns about climate change have heightened the need for effective methods for estimating and mapping Biomass and Carbon stock at local, national, continental, and global scales. Reliable Biomass and Carbon stock quantification and spatialization is a challenge, especially in degraded Mediterranean Cork oak forest. To estimate and map Biomass (Btree−Total) and Carbon stock (Cst−total), we explored an improved approach using extracted metrics collected by Lidar-UAV (unmanned aerial vehicles Lidar), combined with forest inventory data. We approach three types of models for data analysis: Simple linear regression, multiple linear regressions, and stepwise multiple linear regression. The best Biomass and Carbon stock model fit is the Stepwise multiple linear regressions, involving the following metrics: maximum elevation, canopy cover and point cloud density and intensity. Our finding provides a quantification and spatialization Biomass and Carbon stock model based on Lidar-UAV metrics in Cork Oak Mediterranen forest and the results confirm the degraded state of Maamora Forest with a Biomass and Carbon stock relatively medium to low.

Monitoring ink disease epidemics in chestnut and cork oak forests in central Italy with remote sensing

Forests provide multiple ecosystem services including water and soil protection, biodiversity conservation, carbon sequestration, and recreation, which are crucial in sustaining human health and wellbeing. Global changes represent a serious threat to Mediterranean forests, and among known impacts, there is the spread of invasive pests and pathogens, often boosted by climate change and human pressure. Remote sensing can provide support to forest health monitoring, which is crucial to contrast degradation and adopt mitigation strategies. Here, different multispectral and SAR data are used to detect the incidence of ink disease driven by Phytophthora cinnamomi in forest sites in central Italy, dominated by chestnut and cork oak respectively. Sentinel 1, Sentinel 2, and PlanetScope data, together with ground information, served as input in Random Forests to model healthy and disease classes in the two sites. The results indicate that healthy and symptomatic trees are clearly distinguished, whereas the discrimination among disease classes of different severity (moderate and severe damage) is less accurate. Crown dimension and sampled spectral regions are a critical factors in the selection of the sensor; better results are obtained for the larger chestnut crowns with Sentinel 2 data. In both sites, the red and near infra-red bands from multispectral data resulted well suited to monitor the spread of the ink disease.

Early Growth and Physiological Acclimation to Shade and Water Restriction of Seven Sclerophyllous Species of the Mediterranean Forests of Central Chile.

The success of using active restoration in Mediterranean-type climate zones mostly depends on an appropriate matching of plant species and specific management prescriptions upon establishment. In this study, we assessed the early growth and short-term physiological acclimation of seven common species found in the sclerophyllous forests in central Chile to water restriction and shading. We established a nursery experiment that included three treatments (T0: sun-exposed and water-restricted, T1: sun-exposed and fully irrigated, and T2: shaded and fully irrigated) and seven tree species differing in their shade and drought tolerance (Quillaja saponaria Molina, Aristotelia chilensis (Mol.) Stuntz, Peumus boldus Molina, Lithraea caustica (Mol.) Hook. and Arn, Luma apiculata (DC.) Burret, Colliguaja odorifera Molina, and Escallonia pulverulenta (Ruiz and Prav.) Pers). We measured the increment in seedling height and different leaf morpho-physiological traits during two months in the dry season. Based on the measured traits, none of the species took advantage of the higher water availability in T1 relative to T0, but most of the species responded to the shade in T2, regardless of their shade or drought tolerance. Height increments due to shade varied from 0% in P. boldus to 203% in L. apiculata. Overall, all the species responded similarly to the treatments in specific leaf area, chlorophyll content index, photosynthetic rate, stomatal conductance, and intrinsic water use efficiency. This suggests that the species exhibited similar acclimation patterns of these parameters to shade and drought, even regarding the variation in midday xylem water potential found in the water-restricted treatment T0 (from -1.5 MPa in P. boldus to -3.1 MPa in E. pulverulenta). In this study, shading had a higher positive effect on the seedling performance of sclerophyllous species than watering, which at operational level highlights the need for investing in tree shelters when using these species in restoration programs.

The return of tall forests: Reconstructing the canopy resilience of an extensively harvested primary forest in Mediterranean mountains

Understanding recovery times and mechanisms of ecosystem dynamics towards the old-growth stage is crucial for forest restoration, but still poorly delineated in Mediterranean. Through tree-ring methods, we reconstructed the return of a tall canopy after severe human disturbance in a mixed beech (Fagus sylvatica) and silver fir (Abies alba) forest, located at a mountain site in the southern edge of both species' range (Gariglione, south Italy). The primary forest was extensively harvested between 1930 and 1950, removing up to 91 % of the biomass. Growth histories, climate-growth relationships and time-series of growth dominance in Gariglione were compared with a network of protected mature and old-growth beech forests distributed along a wide elevational gradient in the same region. We found that the renewed tall canopy of Gariglione is mainly composed of remnant trees, which include uncut trees and saplings, and the post-harvesting regeneration mostly represented by fir. Canopy beech trees reached maximum basal area increment (BAI) in the 1970s, 40–50 years after cutting. Then, beech BAI shifted towards negative trends in phase with drying climate (PDSI), while fir maintained a sustained growth until 2000. This growth asynchrony between the two species conferred community stability over the last decades. The network comparison highlighted the common negative impact of summer drought on high-frequency growth signals of beech in south Italy. However, analysis of long-term mean growth trends indicates decreasing BAI limited to Gariglione beech, revealing relevant differences due to site ecology and its interactions with legacy effects of past management in driving growth responses to climate change. Indeed, lowland mature beech forests showed increasing BAI in the last decades, while primary high-mountain forests displayed a remarkably stable low oscillating growth. In all the Mediterranean forests we studied, large and old trees showed a marked growth acclimation despite ongoing climate warming, demonstrating the effectiveness of landscape rewilding.

Direct and Remote Sensing Monitoring of Plant Salinity Stress in a Coastal Back-Barrier Environment: Mediterranean Pine Forest Stress and Mortality as a Case Study

The increase in atmospheric and soil temperatures in recent decades has led to unfavorable conditions for plants in many Mediterranean coastal environments. A typical example can be found along the coast of the Campania region in Italy, within the “Volturno Licola Falciano Natural Reserve”, where a pine forest suffered a dramatic loss of trees in 2021. New pines were planted in 2023 to replace the dead ones, with a larger tree layout and interspersed with Mediterranean bushes to replace the dead pine forest. A direct (in situ) monitoring program was planned to analyze the determinants of the pine salinity stress, coupled with Sentinel-2 L2A data; in particular, multispectral indices NDVI and NDMI were provided by the EU Copernicus service for plant status and water stress level information. Both the vadose zone and shallow groundwater were monitored with continuous logging probes. Vadose zone monitoring indicated that salinity peaked at a 30 cm soil depth, with values up to 1.9 g/L. These harsh conditions, combined with air temperatures reaching peaks of more than 40 °C, created severe difficulties for pine growth. The results of the shallow groundwater monitoring showed that the groundwater salinity was low (0.35–0.4 g/L) near the shoreline since the dune environment allowed rapid rainwater infiltration, preventing seawater intrusion. Meanwhile, salinity increased inland, reaching a peak at the end of the summer, with values up to 2.8 g/L. In November 2023, salts from storm-borne aerosols (“sea spray”) deposited on the soil caused the sea-facing portion of the newly planted pines to dry out. Differently, the pioneer vegetation of the Mediterranean dunes, directly facing the sea, was not affected by the massive deposition of sea spray. The NDMI and NDVI data were useful in distinguishing the old pine trees suffering from increasing stress and final death but were not accurate in detecting the stress conditions of newly planted, still rather short pine trees because their spectral reflectance largely interfered with the adjacent shrub growth. The proposed coupling of direct and remote sensing monitoring was successful and could be applied to detect the main drivers of plant stress in many other Mediterranean coastal environments.

Large wildfires alter the potential capacity of fire-prone Mediterranean pine forests to provide wild edible mushrooms over the long term

Projected trends of intensified wildfires due to climate warming and fuel-load accumulation are expected to significantly alter fungal diversity, but we know little about how these changes will impact ecosystem services. We aimed to analyze how large wildfires alter the capacity of fire-prone Mediterranean ecosystems dominated by Pinus pinaster Ait. to deliver the provisioning ecosystem service of mushroom production throughout the post-fire succession. We assessed this at early (<10 years), medium (10-20 years), and late (>20 years) stages after fire, compared to an unburned forest. Our results evidenced that large wildfires significantly reduced the capacity of these forests to provide mushroom harvesting opportunities. This adverse effect was most pronounced in the first few years after wildfire but persisted even after 20 years of post-fire succession. The total fungal species richness, abundance, diversity, and productivity at the post-fire successional stages remained lower than in the unburned forest, failing to reach their pre-fire levels even after two decades. However, the presence of commercially valuable edible fungal species, along with their species richness and productivity, began to recover in the medium and late stages after fire. In the immediate aftermath of the fire, saprotrophic fungal species dominated, while mycorrhizal species became more prevalent during the medium and late stages of secondary succession. Additionally, the abundance and productivity of mycorrhizal species in the late succession stage approached those found in the unburned forest. Soil pH and biochemical variables (microbial biomass C and β-glucosidase enzymatic activity) were key drivers of changes in species composition along the successional stages. This knowledge is essential to guide management solutions aimed at reducing ecosystem service loss and increasing resilience to the new scenario of extreme large wildfire events at shorter fire-free intervals, especially in southern Europe.

Atmospheric deposition patterns in bulk open field precipitation and throughfall in Aleppo pine forest and black pine forest on the eastern Adriatic coast

The Mediterranean region, with its unique ecological characteristics, is particularly sensitive to global environmental changes, including climate change and impact of air pollution.Although Aleppo pine and black pine forests are the most abundant on the eastern Adriatic coast, atmospheric deposition in these forests is poorly studied. Changes in the chemical composition of precipitation as it passes through the tree canopy can lead to soil and groundwater eutrophication, and soil acidification, which affects plant vitality. In this study, the dynamics of ion deposition in Aleppo pine forest (Pinus halepensis Mill.) and black pine forest (Pinus nigra Arnold) on the eastern Adriatic coast are investigated, focusing on throughfall and bulk open field depositions.The aim of our research was to fill the gaps in understanding the influence of tree canopies on deposition fluxes in two different Mediterranean pine stands and to compare total inorganic nitrogen loads with critical loads. Over a period of two years, bulk open field precipitation and throughfall were sampled, measured and analysed using the ICP Forest methodology.The results indicate significant differences in ion deposition between bulk open field and throughfall, with throughfall showing higher values for almost all ions. The highest enrichment ratio was determined for K+. The comparison of the actual inorganic nitrogen load with the critical nitrogen load for Mediterranean pine forests revealed that the inorganic nitrogen load exceeded the critical load in the Aleppo pine forest. Ion deposition increased in the throughfall compared to bulk precipitation, which can be attributed to the seasonality of precipitation, including leaching and long dry periods. These findings enhance our understanding of ion deposition fluxes in vulnerable Mediterranean pine ecosystems and emphasize the need for long-term research on this topic in the actual changing environmental conditions.

Variation in the Health Status of the Mediterranean Gorgonian Forests: The Synergistic Effect of Marine Heat Waves and Fishing Activity.

Over the past thirty years, the red gorgonian Paramuricea clavata in the Mediterranean Sea has faced increasing threats, including heat waves and human activities such as artisanal and recreational fishing. Epibiosis on damaged gorgonian colonies is generally used as an indirect indication of stressed conditions. The density and height of P. clavata and the percentage of colonies affected by epibiosis and entangled in lost fishing gear were monitored to investigate the phenomenon and its trend over time in the Ligurian Sea. Analyses were based on transects collected during ROV campaigns between 2015 and 2022 at depths of 33-90 m. A strong correlation was observed between fishing efforts in the study area and the level of epibiosis. Maximal percentages of colonies affected by epibiosis and entanglement were recorded at depths of 50-70 m. Temporally, marine heat waves before 2019 were identified as the primary cause of damage to P. clavata. The decrease in epibiosis percentages after 2019, despite the 2022 heat wave, may be due to a quick recovery ability of the populations and a reduction in fishing activities during the COVID-19 lockdown in 2020. Long-term monitoring programmes are essential to understand the changes in marine benthic communities exposed to different stressors.

Managing both overstory and understory vegetation mitigates the impact of drought on soil nematode communities in a Mediterranean pine forest

Forest management strategies can effectively mitigate the impacts of drought on tree species, but their effects on soil fauna remain largely unexplored. Among soil organisms, soil nematodes can serve as valuable bioindicators to assess the impact of forest management on soil biodiversity and soil functioning. Consequently, we investigated two related questions in a Mediterranean Pinus halepensis Mill. forest located in southeastern France. First, how do soil nematodes respond to forest management practices? Second, can forest management practices help modulate the effects of Mediterranean summer drought on these soil organisms? We conducted a field experiment in which we explored the influence of two forest management techniques—tree thinning (intense, moderate, or absent) and understory removal (shrubs present or absent)—on soil nematodes before and after the summer drought. We found that only total and bacterivorous nematode abundances were positively influenced by the forest management practices. The highest values were observed under conditions of intense thinning combined with shrub presence, with an average of 97,509 individuals per kg of dry soil. In contrast, the abundances of all nematodes, with the exception of predaceous nematodes, were lower after the summer drought with a reduction ranging from −55 % to −82 %. Total, bacterivorous, and fungivorous nematode abundances were less negatively affected by the summer drought under conditions of moderate thinning when shrubs were present versus absent. More generally, we discovered that bacterivorous and fungivorous nematodes were particularly sensitive to the forest management practices and the summer drought. It is thus apparent that habitat alterations induced by forest management can strongly affect nematode community structure and could therefore prompt shifts in ecosystem functioning. Finally, this study highlights that, in forests, understory vegetation can have significant positive impacts on soil nematode populations when severe dry periods occur.

Exploring climate-smart forestry in Mediterranean forests through an innovative composite climate-smart index

In recent years, Climate-Smart Forestry (CSF) has emerged as an innovative approach to sustainable forest management, aiming to enhance forest resilience and to balance the provision of ecosystem services facing climate-related threats. This study introduces for the first time a new composite climate-smart index (ICSF) to assess CSF. The methodological approach comprises the following steps: (i) the selection and evaluation of CSF indicators; (ii) the weighting of these indicators; and (iii) the assessment of CSF for Mediterranean forests in two distinct periods, specifically 2005 and 2015. Eight indicators were selected from a systematic literature review. The Analytic Hierarchy Process was applied to translate the preferences obtained through an online questionnaire from a network of CSF-expert stakeholders into weights, at both indicators and criteria levels (i.e., adaptation, mitigation, and the social dimension). Results reveals that indicators “tree species composition”, “forest damage”, and “regeneration” are of crucial importance for CSF assessment. The comparison of the CSF value between the years 2005 and 2015, shows a slight increase in CSF ratings. The ICSF serves as a comprehensive index of CSF covering all aspects of that concept, i.e. adaptation, mitigation, and the social dimension (including production). The national-scale analysis provides an overview of the dynamics that involve forest management of Mediterranean forests against climate change. The study offers a practicable method for CSF evaluation with its allover set of indicators, representing a suitable tool for supporting forest managers to mitigate the negative impacts of climate change.