State of research 

Introduction

The climate is becoming increasingly unfavorable for forests. Rising temperatures and reduced precipitation are resulting in more intense and frequent heat waves and droughts, which have significant impacts on the composition, structure, and functioning of forest ecosystems. Global studies, including contributions from scientists at the University of Basilicata, have demonstrated several key effects. Firstly, drought-induced tree mortality and forest decline are widespread across the globe, affecting all biomes and numerous species  [2]. Secondly, drought-induced tree mortality can lead to substantial changes in forest communities, such as the introduction of species from drier environments into temperate forests or the transformation of forests into mixed tree/shrub open-canopy communities [1]. 

Tree mortality and forest decline are on the rise in Italy, with deciduous oak forests being the most severely affected. The vulnerable species include Turkey oak (Quercus cerris L.), downy oak (Quercus pubescens Willd.), Hungarian oak (Quercus frainetto Ten.), and pedunculate oak (Quercus robur L.). Our research group previously documented cases of declining oak forests throughout the Italian peninsula [3], and more recent studies have demonstrated that oak forests are highly susceptible to severe heat waves and droughts  [4]. These issues have been the focus of functional studies in marginal areas of the southern Apennines (Basilicata) and in floodplain forests within protected areas in southern and northern Italy.

In this section, we summarize the findings of research conducted at the University of Basilicata. These ongoing studies, now part of the Agritech project, serve multiple purposes:

• Interpreting the eco-physiological behavior of oak species under drought conditions

• Monitoring and forecasting the temporal dynamics of oak forests under climatic stress

• Defining adaptive management strategies to enhance the resilience of deciduous oak forests

These investigations provide valuable insights for understanding and addressing the challenges faced by Italian oak forests in the context of changing climate conditions.

Tree phenotype and genotype in drought response 

Research into wood anatomical traits has provided valuable insights into predicting drought-induced dieback in Mediterranean ring-porous oak species. A 38-year study (1980-2017) revealed distinct growth patterns and xylem traits between declining and non-declining oak trees, helping to identify key climatic factors contributing to hydraulic failure and tree mortality [17]. The impact of atmospheric nitrogen deposition on drought resistance merits consideration: a meta-analysis suggests that increased nitrogen availability may promote the formation of xylem conduits with improved resistance to drought-induced cavitation [8]. Elevated nitrogen deposition and availability may positively affect oak physiology, enhancing both water use efficiency and carbon uptake [9].

Recent studies emphasize the importance of addressing confounding factors in field conditions and implementing appropriate sampling protocols when investigating relationships between genetic and phenotypic traits. Key findings include: pathogens like Phytophthora quercina may predispose trees to decline [10]; small-scale environmental variability can modify drought effects on forest communities  [4].

These insights highlight the complex interplay of factors influencing tree responses to drought stress and underscore the need for comprehensive, multifaceted approaches in forest ecology research and management.

Intra-specific differences in extreme drought resistance underscore the adaptive potential of tree populations. The Agritech project addresses this by combining ecophysiological, dendro-ecological, and dendro-genomic analyses.

Remote sensing 

We have explored the integration of ground-based observations and satellite remote sensing (RS) to develop methods and metrics for interpreting and predicting oak forest decline. The Normalized Difference Vegetation Index (NDVI), a well-established indicator, has shown strong correlations with ground-based variables such as forest stand basal area and tree growth [11]. A novel metric for quantifying water deficit has been proposed, demonstrating effectiveness in predicting atmospheric conditions conducive to drought  [12]. Remote sensing has proven to be a valuable tool for real-time, large-scale monitoring of drought stress effects on oak forest growth and productivity [13, 14].

The challenge of combining remote sensing and dendroecological methods to assess forest vulnerability and decline has been further examined in a review. This study addressed critical issues, needs, and potential solutions in this interdisciplinary approach. By synthesizing these diverse methodologies, researchers aim to enhance our understanding of oak forest decline and improve predictive capabilities for forest management [19].

Floodplain forests

Floodplain forests in temperate regions are remnants of once-widespread ecosystems. These valuable and now rare habitats, which harbor high biodiversity, face potential threats from climate change-induced alterations in rainfall patterns. The Bosco Pantano of Policoro (Matera, Basilicata, southern Italy) is one such ecosystem, where research and management efforts focus on preserving the relict floodplain forest and its keystone species, the pedunculate oak (Quercus robur L.) [15]. Genetic analyses (to be published) have revealed that the oak population in Bosco Pantano exhibits a unique genetic profile, distinguishing it from other Italian oak populations while also showing signs of genetic depletion. This population likely represents the final remnant of a southern genetic lineage, harboring distinctive adaptations to the Mediterranean climate. These findings underscore the population's ecological significance and its potential importance for conservation efforts in the face of changing environmental conditions.

Interspecific differences also play a crucial role in the conservation of these ecosystems. Recent research has highlighted varying responses to climatic stress among pedunculate oak and its associated species: ash (Fraxinus angustifolia Vahl.), alder (Alnus glutinosa L.), and elm (Ulmus minor Mill.). A comparative study conducted in Bosco Pantano and the Ticino floodplain forest in northern Italy yielded the following insights: Ash proved most vulnerable to environmental stressors in the Mediterranean setting of Bosco Pantano;  oak and elm also showed negative impacts from water scarcity in this southern location; alder demonstrated the highest drought resistance across both study sites. These findings underscore the complexity of floodplain forest ecosystems and the importance of species-specific responses in conservation strategies [16],