Fraxinus angustifolia Vahl as a valuable species in riparian rehabilitation projects. From annual growth to habitat preference of narrow-leaved ash in southern Portugal

Abstract

Mediterranean riverine systems show distinct features due to their marked seasonal pattern. Species present in these environments developed specific functional adaptations to cope with this variability linked to events like floods, droughts and geomorphic natural disturbances. Widespread river and floodplain alteration across Mediterranean regions, turned restoration and rehabilitation of riparian corridors a subject of increasing interest during the last decade. Yet, the complex dynamics of riverine Mediterranean systems and their vegetation communities’ interaction is still under study. Improving our understanding on species functional responses to environmental variability will contribute to successful restoration/rehabilitation through more ecologically and economically efficient projects. It was hypothesized that tree growth is affected by water availability and that trees have higher growth near the water channel and downstream from the river source. In this dissertation, dendrochronology was used to study past tree growth in Fraxinus angustifolia Vahl trees from Odelouca river, in Algarve. Annual growth was analyzed in groups differing in their relative position to the active river channel and distance to catchment source, and analyzed with hydrological, climatic and edaphic factors. Tree position relative to active river channel showed to have the highest impact on mean raw tree growth during the last four decades, followed by soil C/N ratio. High minimum temperature during autumn extended the growing season, a trend associated with climate change and temperature rise in the last three decades in the Mediterranean. Additionally, discharges during spring created favorable conditions when tree growth was more intense. Establishing optimal growth position and ecological conditions for riverine species is important to define principles and guidelines for restoration and rehabilitation projects. Also, global change plays an important role in modulating future responses of vegetation under a changing climate, so understanding past responses can provide important clues for adaptive management