Restore and improve the conservation status of threatened forests by holm oak dieback

Both biotic and abiotic factors are raising concerns about Mediterranean oak forests resilience to climate change, particularly Holm oak (Quercus ilex L.) forests. In the last decade, many drought events impacted this species in several Mediterranean countries, and a widespread decline of holm oak forests has been observed due to a combination of drought and the soil pathogen Phytophthora cinnamoni. In addition, climate change has induced a rise in mean winter temperatures, a seasonal shift of precipitation from summer to wintertime, and a tendency towards heavy rain and prolonged droughts, which are triggering factors for the current decline of holm oak in Mediterranean regions. The resulting reduction in holm oak forest vitality and productivity can ultimately lead to profound changes in ecosystem processes and functions. Previous studies based on tree-ring δ¹³C and SSR genotyping showed that different holm oak populations can differ in their water use efficiency, resulting in different drought tolerance. This study highlighted the potential of this analysis for the selection of seed-bearing genotypes aimed to preserve Mediterranean holm oak ecosystem and improving its forest management. In this context, LIFE RECLOAK project aims to restore and improve the conservation status of threatened forests by holm oak dieback using genotypes characterized by high level of drought tolerance and pathogen resistance. A step-by-step approach will allow the achievement of this ambitious goal over the five years of the project. In the first instance, drought-tolerant and pathogen-resistant genotypes will be selected through a genetic screening based on SSR genotyping and the identification of genetic markers associated with stress tolerance. A mesocosm trial will be carried out to confirm the drought tolerance and the pathogen resistance of the holm oak genotypes. Then, the selected seedlings will be planted in four pilot sites areas located in Mediterranean holm oak forests included in Natura 2000 network and affected by widespread dieback: Monti dell’Uccellina in Parco della Maremma (Tuscany, Italy); Parco della Maddalena (Sardinia, Italy); Muela de Cortes y el Caroche (Valencia province, Spain), Raso del Conejo Forest (Sierra Morena, Andalucia, Spain) and Wied il-Mielaħ u l-Inħawi tal-Madwar (Malta). After that, seasonal and multi-year monitoring for three years after the plantation will begin at each pilot site. The monitoring of pilot sites will be done by visual assessment and through the measurement of plant physiological performances by integrating gas exchange measurements with proximal sensing measures. The effects of reforestation on ecosystem functioning and climate mitigation will be investigated by measuring soil moisture, respiration, and microbial communities’ composition, as well as monitoring understory and overstory vegetation cover and biomass accumulation. Overall, this project will provide a reliable demonstration of restoring forest structure, thereby promoting forestry with conservation objectives and opening the possibility of restoring other Mediterranean areas affected by holm oak dieback.