Abstract
The main impact of land abandonment is the initiation and progression of secondary succession which leads to changes in the cover of vegetation and the overall landscape characteristics. The herein PhD thesis aimed at studying the temporal evolution of land use and cover changes from 1945 to the present. Moreover, the present thesis aimed at studying the differentiation of vegetation during the process of secondary succession. Thessalian Agrafa, where the phenomenon of land abandonment has been already observed, were selected as a case study and the study area of the present research. Mapping of land uses and land cover within the study area was conducted based on orthophotos of the years 1945, 1996 and 2015, and the transitions between the different land cover types were calculated, as well as the intensity of these transitions and the factors related to land cover and land use changes were investigated (Random Forest model). Additionally, vegetation sampling was conducted throughout ...
The main impact of land abandonment is the initiation and progression of secondary succession which leads to changes in the cover of vegetation and the overall landscape characteristics. The herein PhD thesis aimed at studying the temporal evolution of land use and cover changes from 1945 to the present. Moreover, the present thesis aimed at studying the differentiation of vegetation during the process of secondary succession. Thessalian Agrafa, where the phenomenon of land abandonment has been already observed, were selected as a case study and the study area of the present research. Mapping of land uses and land cover within the study area was conducted based on orthophotos of the years 1945, 1996 and 2015, and the transitions between the different land cover types were calculated, as well as the intensity of these transitions and the factors related to land cover and land use changes were investigated (Random Forest model). Additionally, vegetation sampling was conducted throughout the study area. Based on the vegetation data, taxonomic diversity (Hill numbers), functional identity (community weighted means) and functional diversity (functional richness, functional evenness, functional dispersion and functional divergence) were calculated. In addition, standardized effect sizes of functional identity and diversity metrics were calculated. Over the 70-year period of the study, the phenomenon of abandonment of traditional forms of land use was observed to have significant effects on patterns of land use and cover. In particular, a drastic and accelerated reduction of the area of open habitats and their replacement by forests was observed, leading to the large-scale homogenization of the landscape. A total of 16 floristically and ecologically distinct vegetation units were distinguished in the study area, including 461 plant taxa. The distinct identified vegetation units represent four stages of secondary succession. These include early grasslands (early stages), mature grasslands, early scrubland and bracken stands (intermediate stages), mature scrubland, (progressed stages), and forests, (late stages). The differences in the history of land use changes among communities, as well as the disturbances that are submitted to, emerged as the most important factors differentiating the grasslands and scrublands, while the differences among forest communities were mainly attributed to ecological factors. Grassland communities were found to be characterized by significantly higher levels of taxonomic diversity than forest communities but had lower levels of functional richness. As shown by the results the main mechanisms of community assembly affecting early successional stages were related to effects of environmental filtering acting on open habitats. Finally, the functional identity patterns of the distinct vegetation revealed that during the initial stages of succession, short-lived species dominate, which invest in their dispersion and are stress tolerating, while during the final stages of succession, woody species dominate, with phenomena of competition being observed among them. The findings of this thesis highlight the usefulness of the complementary investigation of the different aspects of diversity as well as the history of land use of the investigated plant communities. Finally, the importance of maintaining traditional forms of land use for the protection of biodiversity-rich open habitats is highlighted.
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