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- A new index to assess the state of dune vegetation derived from true colour imagesPublication . Talavera, Lara; Costas, Susana; Ferreira, OscarVegetation on coastal dunes is a key element, as it promotes the growth and stabilization of these landforms while contributing significantly to biodiversity. Physical (e.g. impact of storms), ecological (e.g. animal grazing) and human-related (e.g. farming and recreation) factors may disturb coastal dune vegetation, changing dune dynamics and eventually inducing ecogeomorphic state shifts. Therefore, understanding vegetation dynamics and state turns crucial to predict dune evolution paths. The latter must be supported by observations combined with the development of tools (e.g. indexes) able to detect eventual changes and to automatically categorize the state of the vegetation. Here, a multi-step index to characterise the dune vegetation state (DUVES) was developed and tested in Barreta Island (South Portugal), where grey dune vegetation has declined in recent years. The index was computed using classified true colour orthophotos and orthomosaics derived from UAS (Unmanned Aerial Systems) surveys. Google Earth images were used as complementary data to analyse the evolution trends. The possible sources of disturbance (i.e. human-related activities and gull occupation) were also investigated by comparing their distribution with the vegetation changes. DUVES successfully identified different states of vegetation cover that expressed its stability, perturbation or growth based on temporal changes and allowed the analysis of their evolutionary trends. The distribution of perturbation was mostly associated with gull nesting areas, increasing over time, and to a less extent to human-related activities. The observed grey dune habitat loss was due to replacement of plants typical from this habitat by ruderal species promoted by the positive feedback established between gulls and vegetation. The developed index proved to be of great utility to define dune habitat evolution and understand the associated drivers, being a tool with a wide range of applications, namely for improving future coastal management actions aimed at conserving dune habitats. Moreover, DUVES is potentially transferable due to its easy adaptability depending on the particularities of each study site or goal.
- Controls on blowout evolution in southern Portugal: A 49-year analysisPublication . Talavera, Lara; Costas, Susana; Ferreira, ÓscarBlowouts are wind-formed depressions that help maintain the sediment budget and enhance biodiversity in coastal dunes. However, the drivers controlling their evolution and the temporal scales associated to their genesis, development and decay phases remain unclear. To address this, the morphometric characteristics of a series of blowouts on the Ancao ˜ Peninsula (South Portugal) were digitized using imagery from 1972 to 2021, and used to analyse changes in the number of blowouts, total area, morphometric characteristics (width, length, orientation), and elongation rate over time. These data were compared with metocean time series and human activities, allowing the identification of blowout phases, drivers, and associated temporal scales. This work revealed that the blowout genesis phase primarily arised from the impact of physical external factors (e.g., nonstorm low-to-moderate winds blowing out sand from dune scarp irregularities formerly created by extreme wave events), creating incisions across the foredune crest, and lasted 1 or 2 years. The blowout development phase, still ongoing, was characterized mainly by blowout expansion and rotation of large blowouts from North northeast (NNE) to the East-northeast (ENE) controlled by external physical forces at specific times (e.g., low to-moderate winds) and blowout internal factors (e.g., size and orientation). Complete blowout decay phases were not observed, except the complete artificial sealing of some blowouts due to fencing, which lasted 4 years. These findings suggest that a complete and natural blowout genesis-development-decay cycle could likely take more than five decades, with complex and spatiotemporally variable ecogeomorphic feedbacks driving their evolution. The only phase reversal documented was the reactivation of the artificially sealed blowouts, due to storm impacts. Allowing the dune and blowouts to evolve naturally appears to be the current best approach for the dune management at the studied area.