The potential of Biodiversity for Adaptation Strategies to Global Change in Mediterranean Ecosystems

This PhD thesis addresses the relationships between biodiversity ecosystem functionality specifically for the Mediterranean biome. While much ecological research has elucidated the role of biodiversity in controlling fundamental ecological processes, it has mainly focused on grassland ecosystems since 1990 research has started to focus on tree ecosystems as well. Although experimental evidence clearly demonstrates a general positive relationship between biodiversity and above ground productivity, as well as other ecosystem functions, the same evidence also highlighted how the direction of the effect is also strongly dependent on the community composition and environmental context. In the last two decades, attention has does shifted towards understanding the underlying ecological mechanism that determine the outcome of mixing species. The research mostly focused on investigating the Water Stress Gradient Hypothesis (SGH) and its implications for ecosystem responses to changing water availability and on how herbivory is modulated by diversity. However, it also delves into the multifaceted world of root systems, hyphal production, and fungal communities within mixed forest plantations, assessing their contributions to carbon sequestration and further extends to chlorophyll a fluorescence, emphasizing its role in shaping ecosystem dynamics (ED). Examining monocultures and mixtures composed of two species sheds light on the impacts of biodiversity on these processes. Notably, this research offers insights into the adaptation strategies employed by tree species in response to diverse environmental conditions, particularly regarding herbivore interactions. The findings provide a mechanistic understanding of how tree diversity and species identities influence ecological processes and promote the conservation of mixed-species forest plantations. This study is not confined to merely testing the effects of tree species mixing but endeavors to elucidate the underlying biological mechanisms, employing trait-based approaches. This approach seeks to generalize experimental findings and facilitate science-based recommendations for forest management and silviculture. The study bridges the gap between different trophic levels, emphasizing interactions between producers (trees) and primary consumers (insects). It explores the complementarity and competition dynamics between trees and insect herbivores while considering the overarching theme of drought's impact on ecosystems. In conclusion, this work offers a multifaceted exploration of the intricate relationships between tree species diversity, water availability, and ecosystem functionality in Mediterranean ecosystems. The findings have significant implications for enhancing the ecological and economic benefits of mixed forest plantations while bolstering their resilience in the face of climate change. These results are particularly pertinent to Mediterranean biomes and highlight the potential of mixed forest plantations as nature-based solutions to combat climate change and protect biodiversity.

This PhD thesis explores the link between biodiversity and ecosystem functionality in the Mediterranean biome, focusing on how tree diversity impacts ecological processes. It delves into the positive effects of biodiversity on productivity and other functions, noting these effects vary by community composition and environmental factors. Recent research has shifted towards the mechanisms behind species mix effects, particularly under the Water Stress Gradient Hypothesis (SGH) regarding water availability and herbivory's interaction with diversity. The study also investigates root systems, fungal communities, and their roles in carbon sequestration, alongside the significance of chlorophyll a fluorescence in ecosystem dynamics. By examining both monocultures and two-species mixtures, it sheds light on biodiversity's impact on these processes. Key findings reveal tree species' adaptation strategies to environmental stresses and herbivory, offering a deeper understanding of tree diversity's role in ecological functions and mixed-species forest conservation. The research employs trait-based approaches to uncover biological mechanisms behind tree species mixing, aiming to inform forest management and silviculture with science-backed guidelines. It connects different trophic levels, examining tree and insect interactions under drought conditions, and underscores the importance of tree diversity in enhancing mixed forest plantations' ecological and economic values, especially in Mediterranean ecosystems. This work underscores mixed forests' potential in addressing climate change and biodiversity conservation, presenting nature-based solutions for environmental challenges