| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 9.5 MB | Adobe PDF |
Authors
Abstract(s)
The main objective of this thesis is to study the impacts of morphology, structure and flora transformations on the former reclaimed saltmarshes of Alvor and Arade (Algarve, Portugal) and to understand how these changes can be connected with ecological restoration. The methodological approach used to assess the effects of land-use changes on saltmarshes (Chapter II) relied on combining vegetation surveys and the spatial analysis of historic maps (c. 1800) and aerial photographs (1958-2010), which were analysed to map saltmarsh ecosystems and quantify land-use changes. Additionally, vegetation surveys contributed to the identification of saltmarsh typologies: tidally restored saltmarshes (TRS) and enclosed mixed marshes (EMM). The third Chapter focus on comparing the characteristics of natural saltmarshes with TRS and EMM towards sediment composition and accretion dynamics, linking these with possible consequences for vegetation communities. Accretion rates vary between 0.2 mm/year and 15.53 mm/year. Naturally recovering marshes show lower accretion and higher variability in grain size distribution. TRS present a floristic structure that is similar to natural saltmarshes, while the topographic changes of EMM originate grain size differences but floristic similarities. This is linked with the disturbance gradient that influences floristic diversity. Aiming to improve the ecosystem services provided by saltmarshes, a coastal defence index was developed to respond to missing institutional-periodical data and demanding software, as well as to be of international application (Chapter IV). Landscape metrics were selected according to shape, complexity, and connectivity parameters, and added to average elevation and distance to the coast, for 1972 and 2010. An equation that measures coastal protection was developed, taking into account the results of PCA and the percentage of explained variation of each component. By using this index, target coastal defence parameters can be outlined, strategies for their conservation designed, and ecological restoration considered. Floristic composition and diversity developing in secondary marshes result from passive recovery of former reclaimed marshes. To assess the state of these marshes and to evaluate the feasibility of ecological recovery projects, a combined statistical analysis was applied to understand differences in secondary marshes (TRS and EMM) and international examples of managed realignment. A similarity index was calculated to support these comparisons (Chapter V). Large differences in the floristic composition of Atlantic and Mediterranean saltmarshes hinder the application of managed realignment projects on unmanaged saltmarsh development. Saltmarsh vegetation changes derived from passive recovery develop higher similarity in terms of floristic composition and structure (low, medium and high salt marsh) than active recovery works. Despite the emergence of ubiquitous species, unmanaged saltmarshes are with the local species pool (natural saltmarshes).
Description
Tese de doutoramento, Geografia (Geografia Física), Universidade de Lisboa, Instituto de Geografia e Ordenamento do Território, 2016
Keywords
Teses de doutoramento - 2016