Dottorato in BIOLOGIA AMBIENTALE ED EVOLUZIONISTICA

Titolo della tesi: Conservation and Regeneration of Endemic Tree Species in the Socotra Archipelago under Threats of Overgrazing and Climate Change (Development Of New Technologies For The Restoration Of Degraded Ecosystems)

This thesis provides an integrated framework to understand the major causes of ecosystem degradation on Socotra Island to build monitoring tools, prioritise conservation actions, and provide strategies for preserving the island's endangered flora. Socotra Archipelago, a UNESCO World Heritage Site, hosts endemic tree species such as Boswellia (frankincense) and Commiphora (myrrh). Their population structure show how habitat fragmentation, overgrazing, and climate change endanger biodiversity. Early research into Socotra's ecosystems showed the archipelago's unique evolutionary processes, which have been shaped by its isolation and arid environment. However, complete ecological data remained scarce. By synthesizing multiple studies—ranging from field inventories and exclosure experiments to phytochemical analyses and climate-modeling approaches—this work reveals how anthropogenic pressures and environmental stressors combine to endanger tree species essential for both ecological stability and cultural heritage. One of the most pressing concerns emerging from the research is the pervasive impact of overgrazing on Boswellia and Commiphora. Centuries of pastoralism, previously governed by traditional rangeland management, have given place to free-roaming goats that continuously browse seedlings and saplings. This browsing pressure causes population structures to be skewed towards mature individuals, resulting in "dying ecosystems" in which young cohorts fail to develop. Exclosure tests reveal that, while fencing can reduce seedling mortality caused by livestock, survival rates remain low even inside fences, implying that competition, drought, and soil degradation all hinders regeneration. Field measurements show that many Boswellia species yield viable seeds in high proportions; nevertheless, seedling success is limited by pollination difficulties, particularly in low-density stands, and unfavourable climatic circumstances. Large portions of Socotra's woodlands are thus characterised by low juvenile recruitment and diminishing resistance, emphasising the importance of comprehensive treatments that go beyond simple grazing restrictions. Population fragmentation further compounds the vulnerability of these endemics. Inbreeding and genetic drift put several Boswellia species—including B. nana, B. scopulorum, and B. samhaensis—at immediate risk of extinction because they persist in small, isolated groups. Self-pollination is highly prevalent in low-density stands, which lowers seed viability and fertility rates. However, as evidenced by possibly hybrids and morphotypes on Socotra, island environments can also encourage insular speciation and localised adaptations. Understanding this genetic complexity is essential to developing conservation strategies that, when appropriate, restore gene flow without interfering with ongoing evolutionary processes. Climate change adds another dimension of concern. Modelling efforts on four endemic Commiphora species show that rising temperatures, changing precipitation patterns, and increased cyclone frequency may severely limit viable habitats for some taxa. According to projections, C. planifrons and C. socotrana may lose a significant portion of their range, moving to higher altitudes with limited refugia. These findings mirror similar results for Boswellia, where stands of B. elongata have suffered extensive mortality from recent cyclones. The expected reduction in range highlights the need for proactive climate adaptation measures, such as locating and protecting higher-altitude habitats along with promoting natural migration through habitat corridors, even though localised microhabitats may provide some protection. The role of nursing shrubs in encouraging tree regeneration is an interesting research topic in Socotra. Certain plants in dry and semi-arid environments provide microhabitats that mitigate temperature swings, alleviate moisture stress, and prevent browsing. Observational and experimental data show that woody plants like Boswellia and Commiphora frequently recruit beneath shrub canopies, where seedlings benefit from sheltering environments. However, facilitation differs between shrub species; some could have allelopathic effects, while others are more uniformly beneficial. These findings support incorporating nursing shrubs into restoration techniques, whether by direct sowing beneath selected shrubs or transplanting nursery-grown seedlings into shrub microhabitats. When combined with strategic exclosures, such measures may help stabilise decreasing tree populations in severely grazed areas. Beyond ecological parameters, the thesis also addresses Commiphora’s phytochemical diversity, which has both adaptive and economic significance. Headspace solid-phase microextraction (HS-SPME) and GC/MS analyses show that the distribution of monoterpenes and sesquiterpenes correlates with environmental conditions such as altitude and aridity, suggesting an adaptive role for resin composition. If local communities can create sustainable resin-harvesting methods, this chemical variability may also have socioeconomic benefits. Communities are motivated to preserve mature trees when conservation objectives are linked to the production of valuable aromatic resins, which promotes a mutually beneficial relationship between local livelihoods and biodiversity preservation. Overall, the study found that single-factor treatments are insufficient to protect Socotra's tree species, particularly frankincense and myrrh. Overgrazing, while a major threat, is linked to climatic stress, genetic isolation, habitat fragmentation, and soil degradation. Managing these interrelated difficulties necessitates a comprehensive approach. Protective measures, such as exclosures, must be maintained throughout time and paired with strategies that restore soil fertility, retain moisture, and ensure successful pollination. Genetic investigations could help determine if subpopulations should be connected or kept apart to protect evolutionary divergence. Climate-adaptive planning is similarly important: identifying places that are expected to stay appropriate under future scenarios, managing land use, and, where possible, promoting upward migration of species suffering range contractions. Community-based conservation emerges as a cornerstone, given the island’s deep cultural ties to aromatic resins and pastoral traditions. Encouraging local management through rotational grazing, nursery programs, or certified resin production could help combine economic needs with the ecological imperative to protect these species. The use of nursing shrubs in reforestation provides an accessible, nature-based technique for supporting young trees in environments where water and seedling protection are key constraints. Finally, incorporating resin chemical expertise into larger conservation frameworks may open up new opportunities for sustainable resource management, ranging from pharmacological research to niche markets in cosmetics and traditional medicine. Finally, this thesis illustrates that tackling several sources of degradation is critical to the survival of Socotra's endangered endemic trees. By mapping existing distributions, conducting exclosure and nursing shrub trials, analysing population structures, and modelling climatic hazards, it provides a comprehensive picture of the issues that Boswellia and Commiphora face. Crucially, it proposes solutions—long-term exclosures, aided regeneration with nurse shrubs, and community involvement in sustainable harvesting—that promise to preserve both ecological and cultural qualities. The results highlight how resilient Socotra's flora is in areas where major stresses are reduced, despite the difficulties being severe. It is reasonable to hope that frankincense and myrrh trees will continue to exist in their natural habitats for many more generations by combining ecological study, local knowledge, and an understanding of the island's evolutionary past.