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Monitoring dune vegetation changes and associated driving forces at Culatra Island, Algarve, Portugal
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Abstract(s)
As dunas do sistemas de ilhas barreira suportam uma grande variedade de vegetação que estabilizam e promovem o crescimento das dunas protegendo as zonas costeiras. Os habitats de vegetação diferem entre dunas frontal, interdunar e posterior de acordo com a sucessão evolutiva e a exposição da vegetação a fatores naturais como o vento e ondas. Esses fatores podem ter um efeito significativo sobre a geomorfologia das dunas. Além disso, a geomorfologia das dunas pode influenciar a ecologia, devido a evolução eco geomorfológicos que existem nas dunas costeiras, tais como os fatores reguladores "top down", como a areia eólica, e "bottom up", como as condições para um crescimento ótimo de sucessão comunitária. O sistema de ilhas barreira da Ria Formosa é uma reserva natural protegida desde 1987, esse sistema é constituído por uma lagoa protegida por cinco ilhas barreira e duas penínsulas separadas canais de marés, denominados como barras. Dentro deste sistema de ilhas barreira, a Ilha da Culatra contém uma importante comunidade pesqueira, presença de trilhas e colônias locais da gaivota-de-patas-amarelas (Larus Michahellis). Visto que a Ilha da Culatra contém “dunas cinzentas” que estão listadas como um tipo de habitat prioritário, de acordo com a diretiva europeia, foi necessário realizar um estudo rentável sobre o estado da vegetação. Foram investigados fatores que possam contribuir para a perturbação do sistema de vegetação das dunas da ilha da Culatra. O estudo na presente dissertação, desenvolveu um índice para calcular a perturbação da vegetação dunar dentro da Ilha da Culatra utilizando técnicas de detecção remota com a utilização de Sistemas de Informação Geográfica (SIG). Os materiais utilizados para a análise foram ortofotografias e imagens do Google Earth. Estes materiais e ferramentas permitiram classificar a vegetação para completar um índice de perturbação da vegetação. O índice foi realizado através da composição colorida de ortofotografias a cores verdadeiras. Para complementar os dados, foi também utilizada a imagem do Google Earth. As fontes de perturbação foram identificadas pela sobreposição de elementos antropogénicos digitalizados. Este estudo identificou a mudança no estado da vegetação de 2005 para 2017, envolvendo o aumento da perturbação. Constatou-se que a principal causa desta perturbação estava relacionada com marcas causadas por veículos na ilha. O índice e os métodos destacaram a necessidade da utilizar imagens de melhor qualidade, que podem ser de grande utilidade para estudos futuros devido à simplicidade dos métodos e à sua abordagem rentável. Além disso, este método e índice pode ser altamente transferível para outros sistemas dunares e pode ser utilizado como base de referência para o estudo posterior da vegetação dunar na ilha da Culatra, chamando a atenção e importância para a conservação do sistema dunar.
Barrier island sand dune systems support a high variety of plant communities, which stabilise and promote growth of dunes protecting inland areas. According to plant succession and exposure, to natural factors such as wind and ocean, vegetation habitats differ between foredune, interdune and backdunes. This can have a significant effect on the geomorphology of the dunes. Moreover, the geomorphology of dunes can influence the ecology, due to the eco-geomorphological feedbacks that exist in coastal dunes such as “top down” (for example aeolian sand) and “bottom up” (such as the conditions for optimal growth of community succession) regulating factors. A protected natural reserve since 1987, the Ria Formosa consists of a lagoon protected by five barrier islands and two peninsulas supported by tidal inlets. Within this barrier system, Culatra Island contains a significant fishing communities, the presence of local footpaths and colonies of the Yellow legged gull (Larus Michahellis). Since Culatra Island contains “grey dunes" which are listed as a priority habitat type according to the EU habitats directive, it was therefore necessary to conduct a cost-effective study on the state of the vegetation and whether any factors are contributing to the perturbation of the Culatra Island dune vegetation system. This study developed an index to calculate dune vegetation perturbation within Culatra island using remote sensing techniques within a Geographical Information Systems environment (GIS). The materials used for the analysis were orthophotos and Google Earth imagery. These materials and tools enabled the ability to classify vegetation to complete a vegetation perturbance index. The index was carried out by the classification of orthomosaicked true colour images. To complement the data, Google Earth imagery was also used. Sources of perturbation were identified by the superimposition of digitized anthropogenic elements. This study identified the change in vegetation state from 2005 to 2017 involving the increase of perturbation. It was found that the main cause of this perturbation was related to track marks caused by vehicles on the island. The index and methods highlighted the need to use better quality imagery but can be of great use for further studies due to the simplicity of the methods and its cost-effective approach. Furthermore, this method and index can be highly transferable to other dune systems and can be utilized as a baseline for further study of dune vegetation on Culatra island, drawing attention and importance to the conservation of the system.
Barrier island sand dune systems support a high variety of plant communities, which stabilise and promote growth of dunes protecting inland areas. According to plant succession and exposure, to natural factors such as wind and ocean, vegetation habitats differ between foredune, interdune and backdunes. This can have a significant effect on the geomorphology of the dunes. Moreover, the geomorphology of dunes can influence the ecology, due to the eco-geomorphological feedbacks that exist in coastal dunes such as “top down” (for example aeolian sand) and “bottom up” (such as the conditions for optimal growth of community succession) regulating factors. A protected natural reserve since 1987, the Ria Formosa consists of a lagoon protected by five barrier islands and two peninsulas supported by tidal inlets. Within this barrier system, Culatra Island contains a significant fishing communities, the presence of local footpaths and colonies of the Yellow legged gull (Larus Michahellis). Since Culatra Island contains “grey dunes" which are listed as a priority habitat type according to the EU habitats directive, it was therefore necessary to conduct a cost-effective study on the state of the vegetation and whether any factors are contributing to the perturbation of the Culatra Island dune vegetation system. This study developed an index to calculate dune vegetation perturbation within Culatra island using remote sensing techniques within a Geographical Information Systems environment (GIS). The materials used for the analysis were orthophotos and Google Earth imagery. These materials and tools enabled the ability to classify vegetation to complete a vegetation perturbance index. The index was carried out by the classification of orthomosaicked true colour images. To complement the data, Google Earth imagery was also used. Sources of perturbation were identified by the superimposition of digitized anthropogenic elements. This study identified the change in vegetation state from 2005 to 2017 involving the increase of perturbation. It was found that the main cause of this perturbation was related to track marks caused by vehicles on the island. The index and methods highlighted the need to use better quality imagery but can be of great use for further studies due to the simplicity of the methods and its cost-effective approach. Furthermore, this method and index can be highly transferable to other dune systems and can be utilized as a baseline for further study of dune vegetation on Culatra island, drawing attention and importance to the conservation of the system.
Description
Keywords
Dune vegetation mapping Dune vegetation index Vegetation classification True colour images Orthophotography Geographical information systems.