The aim of this work is to evaluate the evolution of the vegetation cover in areas subject to gravel extractions carried out in the last 50 years in the Magredi area of the Cellina and Meduna river (Friuli-Venezia Giulia), an area of great naturalistic importance declared as Special Area of Conservation according to the Habitats Directive. The analysis was divided into two parts. In the first part, the temporal variation of the coverage was evaluated through the analysis of orthophotos and aerial photos. In the second, the variations in coverage were studied through phytosociological surveys carried out in the field. The years of vegetation cover assessment taken into account for the Cellina River are: 1977, 1984, 1993, 2000 and 2018, while for the Meduna River they are: 1976, 1984, 1993, 2000, 2006, 2012 and 2018. For the first part, orthophotos and aerial photos in gray tones from various sources were used (online site of the Military Geographical Institute, Region and Civil Protection of Friuli-Venezia Giulia). Through the QGis software, the areas in which the gravel extractions took place in the times taken into consideration were identified. On the basis of the intensity of gray (lighter and darker tones indicate respectively lower and higher vegetation coverage) in the photos of the various years following that of the gravel extraction, the percentage of soil covered by vegetation was estimated. 27 areas were analyzed for the Cellina River and 111 areas for the Meduna river. In the field, botanical surveys were carried out in 42 sampling areas in the Meduna River, in which the types of vegetation present and the various environmental characteristics, including the type of substrate, were identified. Three categories of this last variable were identified: unexcavated areas, unlevelled screened gravel, and levelled screened gravel. In the analysis of these data, additional existing phytosociological surveys were added, for a total of 94 surveys analyzed. The study carried out showed that in the Magredi vegetation cover depends on several environmental variables, and in particular on the type of substrate, on the time elapsed after the last gravel extraction and on the number of species of the families other than grasses and legumes. For the first variable it was found that the unlevelled screened gravel are substrates very unsuitable for the establishment of plant species, compared to the levelled screened gravels and the unexcavated areas. Forty and more years after gravel extraction, the plant covers are respectively equal to about 30, 60 and 78%. From this result, it follows that the simple leveling of the screened gravel represents an inexpensive intervention to increase the recolonization speed in the Magredo areas after gravel extraction. It was also found that the trend of vegetation cover tends to increase rapidly in the first 20-25 years after gravel extraction, and then it reaches a value beyond which further change occurs very slowly. This trend was also observed for the number of species that increases quickly in the initial phase, and then remains steady. Through this study it was possible to evaluate for the Magredi of the Cellina and Meduna river the evolution of the post-gravel extraction vegetation cover in relation to various environmental parameters, obtaining results not only of scientific interest but also important for a reduction of the impacts of the anthropogenic interventions which were carried out for decades in these environments.
Il presente lavoro ha come scopo quello di valutare l’evoluzione della copertura vegetale insediata in aree sottoposte a interventi di sghiaiamento effettuati negli ultimi 50 anni nell’area dei Magredi dei fiumi Cellina e Meduna (Friuli-Venezia Giulia), area di grande importanza naturalistica dichiarata Zona Speciale di Conservazione ai sensi della Direttiva Habitat. L’analisi è stata divisa in due parti. Nella prima è stata valutata la variazione temporale della copertura tramite l’analisi di ortofoto e foto aeree. Nella seconda le variazioni di copertura sono state studiate tramite rilievi fitosociologici svolti in campo. Gli anni di valutazione della copertura vegetale presi in considerazione per il fiume Cellina sono: 1977, 1984, 1993, 2000 e 2018, mentre per il fiume Meduna sono: 1976, 1984, 1993, 2000, 2006, 2012 e 2018. Per lo svolgimento della prima parte sono state utilizzate ortofoto e le foto aeree in toni di grigio provenienti da varie fonti (sito online dell’Istituto Geografico Militare, Regione e Protezione Civile del Friuli-Venezia Giulia). Tramite il software QGis sono state individuate le aree in cui sono avvenuti gli interventi di sghiaiamento nelle varie epoche prese in considerazione. Sulla base dell’intensità di grigio (toni più chiari e più scuri indicano rispettivamente copertura minori e coperture maggiori) nelle foto dei vari anni successivi a quello dello sghiaiamento è stata stimata la percentuale di suolo coperto da vegetazione. In questa prima parte sono state analizzate per il fiume Cellina 27 aree e per il fiume Meduna 111 aree. In campo si è proceduto con il rilevamento floristico in 42 aree di saggio nel fiume Meduna, in cui sono stati identificati i tipi di vegetazione presenti e le varie caratteristiche ambientali, tra cui il tipo di substrato. Di questa ultima variabile sono state individuate tre categorie: aree mai sghiaiate, sghiaiate vagliate e sghiaiate non vagliate. Nell’analisi di questi dati sono stati aggiunti ulteriori rilievi fitosociologici esistenti, per un totale di 94 dati analizzati. Dallo studio compiuto è risultato che nei Magredi la copertura vegetale dipende da più variabili ambientali, e in particolare dal tipo di substrato, dal tempo trascorso dopo l’ultimo sghiaiamento e dalla numerosità delle specie delle famiglie diverse dalle graminacee e leguminose. Per la prima variabile è stato osservato come i substrati vagliati non spianati rappresentano dei suoli poco idonei all’insediamento delle specie vegetali, rispetto ai substrati vagliati spianati e ai non vagliati. Quaranta e più anni dopo lo sghiaiamento le coperture vegetali che si raggiungono sono rispettivamente pari a circa 30, 60 e 78%. Da tale risultato deriva che il semplice spianamento dei vagliati rappresenta un intervento gestionale poco costoso per migliorare la rapidità di ricostituzione delle fitocenosi di magredo dopo gli sghiaiamenti. Si è osservato anche che l’andamento della copertura vegetale tende ad aumentare rapidamente nei primi 20-25 anni dopo lo sghiaiamento, per poi raggiungere un valore oltre il quale la variazione è molto limitata. Questo andamento della copertura si osserva anche per la numerosità delle specie che aumenta in modo veloce nella fase iniziale, per poi assestarsi. Attraverso questo studio è stato possibile valutare per i Magredi dei fiumi Cellina e Meduna l’evoluzione della copertura vegetale post-sghiaiamento in relazione a vari parametri ambientali, ottenendo risultati non solo di interesse scientifico ma anche importanti per una riduzione degli impatti degli interventi antropici da decenni esercitati in questi ambienti.
Evoluzione post-sghiaiamento in vegetazioni fluviali del Friuli-Venezia Giulia
DE IORIS, ELENA
2021/2022
Abstract
The aim of this work is to evaluate the evolution of the vegetation cover in areas subject to gravel extractions carried out in the last 50 years in the Magredi area of the Cellina and Meduna river (Friuli-Venezia Giulia), an area of great naturalistic importance declared as Special Area of Conservation according to the Habitats Directive. The analysis was divided into two parts. In the first part, the temporal variation of the coverage was evaluated through the analysis of orthophotos and aerial photos. In the second, the variations in coverage were studied through phytosociological surveys carried out in the field. The years of vegetation cover assessment taken into account for the Cellina River are: 1977, 1984, 1993, 2000 and 2018, while for the Meduna River they are: 1976, 1984, 1993, 2000, 2006, 2012 and 2018. For the first part, orthophotos and aerial photos in gray tones from various sources were used (online site of the Military Geographical Institute, Region and Civil Protection of Friuli-Venezia Giulia). Through the QGis software, the areas in which the gravel extractions took place in the times taken into consideration were identified. On the basis of the intensity of gray (lighter and darker tones indicate respectively lower and higher vegetation coverage) in the photos of the various years following that of the gravel extraction, the percentage of soil covered by vegetation was estimated. 27 areas were analyzed for the Cellina River and 111 areas for the Meduna river. In the field, botanical surveys were carried out in 42 sampling areas in the Meduna River, in which the types of vegetation present and the various environmental characteristics, including the type of substrate, were identified. Three categories of this last variable were identified: unexcavated areas, unlevelled screened gravel, and levelled screened gravel. In the analysis of these data, additional existing phytosociological surveys were added, for a total of 94 surveys analyzed. The study carried out showed that in the Magredi vegetation cover depends on several environmental variables, and in particular on the type of substrate, on the time elapsed after the last gravel extraction and on the number of species of the families other than grasses and legumes. For the first variable it was found that the unlevelled screened gravel are substrates very unsuitable for the establishment of plant species, compared to the levelled screened gravels and the unexcavated areas. Forty and more years after gravel extraction, the plant covers are respectively equal to about 30, 60 and 78%. From this result, it follows that the simple leveling of the screened gravel represents an inexpensive intervention to increase the recolonization speed in the Magredo areas after gravel extraction. It was also found that the trend of vegetation cover tends to increase rapidly in the first 20-25 years after gravel extraction, and then it reaches a value beyond which further change occurs very slowly. This trend was also observed for the number of species that increases quickly in the initial phase, and then remains steady. Through this study it was possible to evaluate for the Magredi of the Cellina and Meduna river the evolution of the post-gravel extraction vegetation cover in relation to various environmental parameters, obtaining results not only of scientific interest but also important for a reduction of the impacts of the anthropogenic interventions which were carried out for decades in these environments.| File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12608/35821