Stato di conservazione delle comunità psammofile in relazione ai cambiamenti territoriali e ai fattori di disturbo agenti nel tratto costiero della Provincia di Viterbo
Author(s)
De Luca, Elena
Date Issued
February 10, 2011
Type
Doctoral Thesis
Abstract
The second half of last century has witnessed the transformation and development of coastal areas with significant effects on the distribution of mobile dunes. Changes at sea and on land lead to changes in the shoreline that can be considered “geo-indicators” as they also have repercussions on the ecosystems beyond. Healthy dune systems are key to reducing coastal erosion caused by sea and wind.
Coastal erosion and anthropogenic pressures, such as the expansion of urban settlements, the abandonment of traditional land management practices and the development of seaside tourism have led to the fragmentation and, in some cases, to the disappearance of psammophilous coenoses associated with mobile dunes in Italy as in the rest of Europe. There is therefore a pressing need for the development of appropriate monitoring methods and conservations strategies of these highly threatened coenoses.
Plant communities are characterized by diverse responses to impacts and are the basis for the functional dynamic equilibrium of the dune. The sequence of psammophilous coenoses has been found to be directly correlated with the slope and the aspect of sand dunes. Causing disappearance of some coenoses, stress factors influence the sequence of plant communities, endangering the relationships that allow these vegetation types to live in extreme conditions.
This thesis is a contribution to the study and understanding of the processes that affect coastal systems, considering the factors that over time have resulted in changes that underlie these processes. A further objective is to describe the status of such systems in the coast of the Viterbo province, Latium Region, Italy, highlighting critical issues and peculiarities. The approach used is multiscale and extends both the spatial and temporal dimension.
At the macroscale, a diachronic analysis was conducted to identify changes between the late 1950s and 2005 in the coastal stretch considered. The analysis was undertaken using GIS through the comparison of land use maps resulting from georeferencing, mosaicking and photo interpretation of aerial panchromatic photographs GAI (Gruppo Aeronautico Italiano) (1954) and digital aerial photographs AGEA (Agenzia per le Erogazioni in Agricoltura) (2005). Sufficiently generic land use classes were identified for comparison of these layers with different resolution levels. Overlapping maps, recording consistency and/ or changes in each polygon, allowed the editing of the “Map of land use change 1954-2005”, which highlights changes in land use while providing qualitative and quantitative information.
To validate the findings of diachronic analysis, a comparison was made with statistical data from the 1st and the 5th General Census of Agriculture of ISTAT (1960 and 2000) (National Institute of Statistic) and the resident population in 1961 and 2000. Agricultural intensification, urbanization of
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croplands and deforestation for farming are the main pressure factors on this area. Coastal erosion affects mainly the coast of Tarquinia while Montalto di Castro presents stretches of coast that are stable, in progress or eroded. The application of landscape metrics on the two land use maps showed patterns that consist of a high degree of beach, scrub, forest and grassland fragmentation.
This study also describes the conservation status and distribution of psammophilous coenoses in relation to disturbance factors in the coastal stretch considered. Particular emphasis was given to the bio indication value of plant communities and their sequence. Each plant community was considered as a “habitat” in accordance with Annex I of the Directive 92/43/EU. Various stress factors and anthropogenic pressures influence the sequence of habitats and can weaken the system of relationships that allow these coenoses to occur in extreme conditions. Surveys carried out along wide transects, recording multiscale data such as land classes, habitat coverage, plant assemblages and type of disturbance, allowed the use of habitats as bioindicators. By comparing sites characterized by the similar extensions in homogeneous areas, it was possible to use Canonical Correspondence Analysis (CCA) as a tool to correlate habitat composition to disturbance factors. The application of CCA showed a high correlation of degradation and habitat loss with coastal erosion, trampling and presence of waste. Furthermore, different biodiversity indices were calculated based on floristic surveys conducted to quantify species richness of sampled areas. The conservation status of the sites was found to be diverse, from the total disappearance of the mobile dune habitats to their complete sequence. Surveys carried out along wide transects recording habitat coverage were performed with the aim of establishing the conservation status of dune systems in relation to disturbance factors using habitats as environmental indicators. Comparing sites characterized by the same extension in a homogeneous area, it was possible to expand the use of CCA analysis on habitat composition. Vegetation of the driftline (code 1210) and shifting dunes with Ammophila arenaria (code 2120) are the most sensitive habitats. Juniperus scrub (code 2250) is severely damaged by sea sprays, where mobile dune is absent, or disappears as a result of urbanization in the areas behind the mobile dunes. Natural wetland are extremely rarefied. It would be desirable to promote studies aimed to the characterization of residual areas such as on the coast of Pescia Romana, Pian dei Gangani and near the mouth of Arrone river.
While erosion strongly affects mobile dune habitat, CCA analysis shows that beach use does not necessarily coincide with habitat decay. Rather, uncontrolled use of the beach with trampling and waste abandonment causes mobile dune habitat loss. Low impact recreational activities, based on beach use within delimited routes that avoid trampling on the mobile dune, are recommended as desirable sustainable tourism strategies in this area.
The application of diversity indices is an important tool to quantify species richness on dunes. However, in particular environments consisting of strongly interrelated habitats, does not always give appropriate results. HDUNE diversity index better described the conservation degree of communities associated with the mobile dunes.
The proposed methodology has been shown to be effective in fulfilling the study objectives and has potential application for other case studies in the Mediterranean.
Additional information
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche
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