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Bremen University (2003)

Vegetation ecological studies at the lower course of Sabor River (Tras-os-Montes, NE-Portugal)

Hoelzer André

Titre : Vegetation ecological studies at the lower course of Sabor River (Tras-os-Montes, NE-Portugal)

Auteur : Hoelzer André

Université de soutenance : Bremen UNiversity

Grade : Diploma Thesis 2003

Résumé
A vegetation ecological study was conducted at the lower course of Sabor river, northeastern Portugal. The valley of this river constitutes an agroecosystem with typical Mediterranean traits and is known for its diversity of habitats with conservational value. The valley suffered from considerable abandonment of agricultural areas over the past four decades, whereas the extension of not intervened vegetation increased substantially. However, the whole extension of the lower course of this river is endangered by the construction of a hydroelectric power plant, and submersal of huge areas will be an immediate impact. In order to characterize the floristic-structural dynamics and diversity of the vegetation covering the valley, representative samples of different communities at different altitudes along the river valley were taken. In all, 109 relevés with an homogeneous area of 10 x 10 m2 comprised a section of the river with an extension of 30 km. Samples were classified into distinct types of communities, according to their structure : riparian communities, rupicolous communities, scrublands, woodlands and grove communities. Two basic approaches were applied to examine the ecology of vegetation. First, the total species numbers within the different samples were compared. Riparian communities proved to be the richest in terms of species, and species numbers were higher than 60/100 m2 in several cases. A strong concentration of diversity coincided with the immediate riverside zone, whereas other environmental factors did not explain significantly the concentration of species. The communities subjected to agricultural intervention were the second richest community type in terms of species numbers. By far the highest percentage of all registered species pertained to a therophytic life form. The second approach was based on multivariate statistical analysis of the data set constituted by the samples. According to a recent methodology that permits description of floristic-structural dynamics, different structural parameters were focussed to build structural matrices : specific diversity, abundance, stratification and conjoint data matrices of these parameters. The introduction of stratification constitutes an extension in relation to the original framework of the methodology and proved to be useful to further describe vegetation structure. Several tendencies of structural expression were detected that constituted in different degrees the apparent community types. The communities were found to exhibit high degrees of dynamics between each others, but also the intracommunitarian dynamics turned out to be high. This may be an explanation for a high degree of superimposition detected between the various community types in floristic-structural terms. A basic feature found was the structural similarity, regardless considerable differences according to the envisaged parameter, in terms of representation of life forms, but a different specific composition, indicating that to a higher extension functionally homologous species could contribute to maintain structural dynamics and diversity. Contrasting the obtained results with information about the magnitude of agricultural impact in the different sites and site history, a tendency to increase higher variability of floristic-structural combinations within the communities in the course of regenerating succession processes was suggested. The singularity of riparian communities was corroborated both in terms of structural diversity and the fact that species with low frequencies over the whole area reached highest expressions within this community type. It is suggested that riverside communities exert a significant influence upon all other community types with more upland characteristics, as indicated by the transmission of supposed riparian tendencies into other types, thus having provided potential for the observed rapid ecosystem restoration. Considering the dependence of this community type upon the fluvial dynamics in force, it is expected that the impact of the hidroelectric power plant would not only affect the riverside vegetation, but equally the vegetation out of the immediate influence zone of the future lagoon

Version intégrale (ResearchGate)

Page publiée le 7 mars 2016, mise à jour le 19 janvier 2018