Maria Castellaneta

Key message: Drought resistance and resilience in Mediterranean oaks appear to be structured along axes of variation linked to leaf habit and wood anatomy. Recurrent and intensifying droughts have emerged as a principal driver of decline in Mediterranean oak forests over the past three decades. This review synthesizes current understanding of the functional mechanisms shaping drought impacts in these ecosystems and complements existing work by combining a structured categorical overview with a multivariate functional ordination of oak responses. We assembled a dataset of 240 records derived from 212 studies published between 1994 and 2024, spanning species with contrasting leaf habits (evergreen, deciduous, semi-persistent), diverse wood anatomies (diffuse-, ring-, and semi-ring-porous), and developmental stages ranging from seedlings to mature stands. The studies encompass a broad gradient of drought durations and intensities, enabling comparison of drought resistance and resilience across plant systems. Across the reviewed literature, key ecophysiological mechanisms include stomatal regulation, hydraulic and osmotic adjustment, morpho-anatomical plasticity, and phenological shifts. However, most studies investigate these mechanisms in isolation, and integrative, multi-trait analyses remain rare. Using coarse categorical metrics, we found no clear geographic structuring of resistance, resilience, or response mechanisms, likely reflecting uneven species representation and heterogeneous experimental designs. Nonetheless, the dataset reveals functional patterns linked to plant diversity: deciduous, ring-porous species exhibit higher frequencies of low-resistance and low-resilience states, whereas evergreen, diffuse-porous species tend to display greater hydraulic safety and recovery capacity. Correspondence analysis further highlights major axes of variation associated with leaf habit and wood anatomy, confirming divergent adaptive strategies among Mediterranean oak functional types. Collectively, these findings underscore the importance of functional diversity in shaping drought responses and provide a framework for future mechanistic research and climate-adapted forest management.

Climate-induced forest mortality is an increasing global phenomenon occurring at both regional and local scales, with implications for ecosystem functioning and the provision of essential ecosystem services. In recent years, the Italian peninsula has experienced widespread oak forest decline, with forests showing increased susceptibility to severe heat waves and prolonged droughts. Our study examined a drought-induced tree mortality episode in the Mediterranea region (Pollino National Park, Southern Italy) focusing on deciduous oak forest stands (Quercus frainetto Ten.). We employed a comprehensive approach, combining ecophysiological and dendro-ecological analyses to compare non-decaying (ND) and decaying (D) coexisting trees. Recent advancements in understanding the relationship between petiole xylem anatomy and leaf form and function have revealed a positive correlation between petiole vessel diameter and leaf size, both within and across species. Leaf petioles, serving as the singular entry point for water into the leaf venation system, offer a standardized basis for comparing xylem investment with downstream transpirational demands. To quantify this relationship, we employed a novel index derived from quantitative wood anatomy of petioles. This integrative trait characterizes leaf water transport function by measuring the ratio of cross-sectional xylem area (XA) at the petiole to the downstream leaf area, termed the XLA petiole Index. Our assessment of XLA petiole variation can provide evidence supporting a safety-efficiency trade-off in oak leaves, a crucial aspect of plant hydraulic strategy.

Over the last years several forest dieback and mortality phenomena were reported across the Italian Peninsula underline an enhanced forest vulnerability due to the occurrence of extreme climate events, such as heat waves and severe droughts. During summer 2024 acute and extensive impacts, with severe defoliation, dieback and mortality, on Mediterranean forests (Quercus ilex, Quercus suber, Phillyrea spp. and several other sclerophyllous shrubs) were detected in various regions of Italy predominantly in Apulia, Sardinia and Sicily. Currently, in Italy as well as in other Mediterranean countries is lacking a clear picture of this emerging phenomenon, of the forest species more sensitive and the quantification of the affected forest surfaces. It is, therefore, necessary to improve the monitoring network within the regional territories to assess environmental drivers and dynamics of impacts with a multidisciplinary approach that includes ecophysiological and phytopathological aspects. In this contest, the SilvaCuore application, the first App designed in Italy by the University of Basilicata and Effetreseizero S.r.l., as a part of a Citizen Science project, can play a key role to survey declining forest stands within the Italian territory. The support of an active users’ community can not only allow researchers to survey declining forest sites, but also to better plan research activities and management measures. Specifically, SilvaCuore is a Web-application that can be used directly from smartphone, tablet or PC, and drives the user in reporting information step by step with few simple clicks thanks to a user-friendly interface. The data to be provided are the tree species, symptom detected (i.e. defoliation, drying crown, bark necrosis etc.), the uploading of some descriptive photos and the geo-localization on the map. In this context, the App allowed to identify most of the affected areas by mapping the extension and contributing to the development of a valuable scientific database in Italy. Monitoring of forest health is crucial for implementing appropriate adaptive management strategies and for improving the resilience of declining stands. Indeed, the selection approach may drive the existing legislation and forest management still ill-suited to the current conditions of forest stands affected by climate change.

The health status of forests is becoming increasingly endangered by drought-induced climate change. In recent decades, widespread forest decline has been reported worldwide in all biomes. The reports of forest mortality across Italy and the need to be better aware of the extent and magnitude of the phenomenon were the assumptions that led to the development of a web-application called SilvaCuore. A team of researchers from the University of Basilicata has carried out this project to safeguard Italian forests. The aim is to combine scientific research and active community participation (Citizen Science project) through the use of new technologies, in order to better monitor and manage Italy’s forest heritage. The SilvaCuore web-application seeks to census the declining forest sites located in Italy and to create a database that can be used as a basis to improve the forest management. SilvaCuore has been developed as a Progressive Web Application and can be accessed from smartphones, tablets and PCs due to its responsive user interface. The user, after registering in to the web-application, is guided by a user-friendly step-by-step procedure in the reporting process that, besides a brief description or more complex data, allows to take some photos and the GNSS position of the site. The report outcomes will be automatically collected in a cloud web database, immediately accessible to the research team. Verified reports will become publicly accessible from the same web-application, ready to provide a concrete insight into the health of our forests. The application is also linked to a website that provides additional information about the project, the rationale behind the app, and the research activities carried out by the SilvaCuore team. It is crucial to improve the citizen's approach to nature and environmental issues: a more aware citizen will be a citizen who cares more about the environment and its preservation. An case in point is the agreement with PEFC Italy (Program for the Endorsement of Forest Certification Schemes): first, PEFC-certified forest owners will be able to utilize the web-application, in order to implement adaptive forest management and second, this will provide useful alert reporting. The challenge here is to be able to create a monitoring network that not only monitors the current state of forest health but also evaluates potential future dynamics, and becomes increasingly capable of responding to the threat of forest decline.

In the current context of climate change, this paper provides a brief overview of climate-vegetation interactions in the Mediterranean basin, where global warming and aridification trends are predicted to intensify. Rising temperatures coupled with extreme drought events have notable impacts on forest ecosystems, triggering dieback and mortality phenomena worldwide. The health status of forest vegetation may be assessed by either ground surveys or remote sensing. Several investigations of declining oak forests in the Apennine region have shown that the drought vulnerability of Mediterranean oaks is dependent on differences in access to deep soil water pools, which can be related to differences in rooting depth, tree size and growth rate. Forest dieback is widely reported in Italy, but the extent and overall distribution of this phenomenon have not yet been well defined. Thus, understanding the future dynamics of forest stands has several key objectives: inventorying declining forest stands to gain insight into the phenomenon and create a national-level database; locating these stands to allow monitoring of their evolution over time; and monitoring to allow planning of mitigation measures, as well as recovery and adaptation strategies. This background led to the implementation of SilvaCuore, the first web application designed in Italy to report forest health status. Silvacuore is a web application developed with the aim of improving the link between citizens and the scientific community by contributing to the development of a valuable scientific database. The direct involvement of citizens in forest preservation offers an interesting perspective because the innovative use of technology can tap into citizens’ growing enthusiasm for environmental topics. Thus, SilvaCuore may be viewed from a dual perspective as a resource for the scientific community and as a unique opportunity for citizens to take an active role in research activities (Citizen Science project).

Forests around the world are facing climate change. Increased drought stress and severe heat waves in recent decades have negatively impacted on forest health, making them more vulnerable and prone to dieback and mortality phenomena. Although the term vulnerability is used to indicate an increased susceptibility of forests to climate change with a worsening of their vigour status that can compromise their ability to respond to further climate extreme events, there are still uncertainties on how to evaluate it. Indeed, evaluation of forest vulnerability is complex both because of some critical issues in the estimation methods used and because of the multiple factors influencing the response of forests to ongoing climate change. A way to assess the vulnerability to environmental stresses is by combining remote sensing and dendroecological data. However, these two approaches entail multiple uncertainties, including growth/photosynthetic relationships, carbon allocation dynamics, biases of tree-ring data and noisy remote sensing data, which require further clarification for proper monitoring of pre- and post-drought forest trajectories. Our review aims to create an overview of the current literature and knowledge to understand the critical issues, needs and possible solutions that forest vulnerability research is addressing. We focus on Mediterranean forests located in a climate warming hotspot and showing a high vulnerability to increased aridification.

Old-growth forests have a primary environmental and ecological value, as they closely recall primeval forests and the natural forest landscape that was spread throughout Italy and Europe before man intervention heavily altered the functioning of most natural ecosystems. These ecosystems are more and more recognized as keystones of environmental policies (i.e., the EU Biodiversity Strategy 2030) aimed to preserve biodiversity and mitigate the impacts of climate change. A recent report highlights that Europe’s old-growth forests account for only 3 percent of the overall forest surface. The majority of italian old-growth forests are located along the Apennines, especially in the Pollino, Sila and Aspromonte National Parks, in remote montane areas characterized by irregular topographical conditions (i.e., high slopes and/or shallow soils) which hamper the access and exploitation of these less productive stands, thus allowing the survival of old-growth forests for many centuries. The ongoing climate change is a significant challenge to the conservation of old-growth forests, particularly in areas such as the Mediterranean basin, where an intensification of extreme climate events is expected. Heat waves can exacerbate drought’s negative impacts on tree growth and survival, leading to reduced woody carbon stocks and biodiversity in old-growth forests. To date, there is poor understanding of such highly valuable and extremely fragile natural ecosystems in Italy. Insights are available based on data gathered as part of two research programs, funded by the Italian Ministry of the Environment and Land and Sea Protection, with the purpose of creating a Network of Old Growth Forests in Italy’s National Parks. In this study, we aimed to highlight the role and importance of old-growth forests, focusing on those located within the Pollino National Park. A comprehensive overview of the key strengths and weaknesses, that mark these peculiar forest ecosystems, was followed by a discussion of the future outlook, grounded on strategies that will ensure not only the protection and conservation of these ecosystems, but also their development and promotion.

Presently, the forests of one of the most economically important tree species in Europe—Norway spruce [Picea abies (L.) Karst.]—have been disrupted and are in rapid decline due to a combination of several natural factors: extreme drought, heatwaves, and secondary damage caused by bark beetle outbreaks. The vulnerability of these forests has increased considerably over the past decade, and remote sensing methods can theoretically improve the identification of endangered forest stands. The main objective was to determine the relationship between remotely sensed characteristics of vegetation (using the normalized difference vegetation index—NDVI) and annual tree-ring growth in 180 trees through precipitation and air temperature. The research was conducted at six research plots in lowland spruce forests (319–425 m a.s.l.) in the central Czech Republic. No significant correlation between NDVI and annual ring width was observed. The primary factor limiting radial growth was lack of precipitation in the growing season; subsequently, spruce trees reacted negatively to air temperatures. A higher correlation with NDVI was observed on sites susceptible to drought, but overall, NDVI and RWI did not show similarities. This result describes that NDVI is a poor indicator for identifying low radial growth in Norway spruce stands on non-native localities in the studied area.

Key message: Managing forest residues according to the carbon content of the soil helps to minimize the ecological footprint of their removal.Context: In Mediterranean mountain ecosystems, unsustainable harvesting of wood residues might contribute to land degradation, carbon, and nutrient depletion in forest soils.Aims: This study aimed to assess the amount of forest biomass residues that should be left on-site to minimize the depletion of soil fertility.Methods: We estimated the availability of biomass residues in the public forest land of the Basilicata region of Southern Italy by collecting stand-scale inventory attributes from forest management plans. Subsequently, we quantified the amount of forest biomass residue released by implementing a scenario-based approach.Results: Approximately 5800 m³ year⁻¹of forest residues could be potentially available for bio-based industries at the regional scale within the next 10 years. Such residues mainly belong to broadleaved forest types, having a high variability in their soil organic stock (228.5–705.8 Mg C ha⁻¹) and altitudinally spanning from 400 to 1500 m a.s.l. In these forests, the simulated scenarios displayed a wide range of average harvestable residues from 2.5 to 5.5 m³ ha⁻¹, containing approximately 1.1 to 2.1 Mg ha⁻¹of organic carbon.Conclusion: Our study suggests that forest management plans are a useful source of information to estimate the available forest biomass residues consistently. In southern Mediterranean mountain forests, the management of forest residues according to soil carbon content helps to minimize the environmental impact and increase their sustainability.