Functional diversity as indicator of ecosystem functioning in Mediterranean riparian forests

Doutoramento em Engenharia Florestal e dos Recursos Naturais / Instituto Superior de Agronomia. Universidade de Lisboa

Riparian forests are ecosystems of high biodiversity and complexity driven by diverse environmental factors and increasingly threaten by anthropogenic pressures. Understanding and predicting vegetation responses to these factors have become one of the most challenging tasks in riparian ecology. This thesis aims to analyze the functional diversity responses of the Mediterranean riparian forests affected by multiple stressors to give insights into ecosystem functioning. The specific objectives were: (i) to assess the worldwide application of functional trait-based approaches in riparian forests; (ii) to determine the key habitat and regional environmental factors that influence the functional diversity of different forests; (iii) to assess the functional diversity patterns of aquatic plants and riparian woody vegetation to streamflow regulation. The results showed that the functional diversity concept has a long history of evolution. Its application to riparian forests has been increasing in the last two decades, with guild approaches becoming more popular than functional diversity indices. Functional richness is the most applied index in riparian plant studies. Amongst the environmental key-factors, precipitation plays a determinant role on the functional diversity of Mediterranean riparian forests, though especially pronounced for Mediterranean shrublands due to their low functional redundancy. Streamflow regulation can foster diverse stress-related functional strategies in contrasting biomes (boreal and Mediterranean), resulting in diverse functional diversity patterns. This result is likely related to a long legacy of adaptations to natural hydrological stress and to the magnitude of streamflow regulation. Further, diverse types of streamflow regulation (run-of-river dams and storage reservoirs) impair differently the cover and functional diversity of bryophytes, vascular macrophytes and riparian woody vegetation. The observed patterns of functional diversity can inform on the conservation status of the Mediterranean riparian forests and allow anticipating the vulnerability of the riparian ecosystems to future changes, which can guide mitigation, conservation or restoration plans

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