Distribution patterns of riparian plant species across river of Sardinia and Tuscany

This research project aims to analyze riparian vascular flora of four Mediterranean rivers belonging to two different regions (Sardinia and Tuscany). It focuses on the analysis of floristic differences, on distributional trends of functional and ecological groups, alien and endemic species, and also on the application of landscape classifications to be used as surrogate in conservation planning. The main goal is to evaluate similarities and differences among these rivers in the frame of a regional scale approach of study, thus contributing to improve the knowledge about their internal dynamics and their linkages with the main environmental factors, useful information for conservation management of these threatened habitats. The first part of the work focuses on distributional patterns of species and examines floristic differences at regional (between regions) as well as at local level (between rivers belonging to the same region), in order to elucidate the main gradients of riverbed floras and to investigate the role played by biogeography in driving riparian plant species distribution. Despite many floristic similarities between the two areas, always emerges the high floristic heterogeneity and the regional differentiation as the main variable affecting the distribution of our riverbed floras, thus confirming the primary role of geography in driving riparian plant species distribution at regional scale. At local level, longitudinal gradient results to strongly affect riverbed flora patterns in our rivers, while lateral gradient has a weak effect at regional scale and a relevant effect only in Tuscany. On the basis of the previous results, the second part was devoted to analyze more consistently endemic and alien flora of Sardinian rivers. This was done using a method to rapidly assess conservation priorities by comparing distribution models of these species along the fluvial corridors. The distributional trend of endemic and alien species resulted in general to follow the decreasing naturalness/increasing human impact gradient going toward the sea, but the study evidenced the presence of different degree of naturalness between the two rivers in general, nevertheless the presence of protected areas in both of them. The most critical areas resulted to be the middle course of the rivers, where endemic species coexist with alien species and overall with high human impact in the surroundings. These resulted to be the areas where should concentrate further conservation efforts. In the third part is tested the variation of riparian plant species composition along a Sardinian river according to lithological features. The analyses were based on field data recorded along Santa Lucia river, where the morphology is influenced by the bedrock-alluvial transition. The results underline that lithological types are the primary drivers in the organization of the riparian plant communities, followed by geomorphology and altitude. Moreover, the change bedrock-alluvial marks the highest species turnover, linked also to a different degree of human disturbance. The results indicate that the degree of bedrock/alluvial influence is an integral component to the patch structure and strongly influences riparian plant distribution patterns in a Mediterranean environment. 2 Starting from the previous findings, and going towards the definition of a morphological classification of rivers, in the fourth part is proposed (and applied in one river as a preliminary test) a method to assess the distribution of plant assemblages along rivers delimiting homogeneous fluvial types using morphological features, quantified with aerial photos and geographic information system software. This method identifies four fluvial types, characterized by well-defined indicator species, functional and ecological groups. Based on the ordination results, dividing fluvial types according to morphological features is justified by environmental and floristic differences, although plant species variability is only partially described. This results illustrate that the fluvial type classification created using this methodology is consistent with natural plant species distribution patterns, and can thus consider as a potential surrogate for riparian plant assemblages in a Mediterranean river with low human impact. Incorporating many landscape classifications in biodiversity surrogate schemes should increase concordance with biotic groups. Following this idea, in the last part is examined the strength of a morphology-based and a land-use based classification in accounting for riparian plant species and functional groups distribution in the four rivers, by applying a measure of classification strength. Moreover, is tested the hypothesis that a cross classification between morphology and land use would be more successful at explaining plant species variation than either of the separate approaches. Despite none of the classifications accounted for a large degree of variation in riparian plant assemblages, some of them performed better than others, suggesting that some factors at landscape scale could contribute to predict differences in biological characteristics at local scales, and that classifications created putting together many environmental variables would result in better performaces. These findings will be useful for better understand distributional trends of riparian flora and above all for prioritizing conservation actions in these areas, considering the threats to which rivers have currently subjected to. ------------------------------------------------------------------------------------------------------------------------- Il presente lavoro di ricerca analizza la flora vascolare ripariale di 4 fiumi mediterranei di 2 regioni diverse (Sardegna e Toscana), al fine di approfondirne le conoscenze riguardo le differenze floristiche, i trend di distribuzione di gruppi funzionali ed ecologici, di specie endemiche e aliene; infine, vengono applicate diverse classificazioni di paesaggio e ne viene testato l'utilizzo come potenziali surrogati per la pianificazione della conservazione. L'obiettivo principale ਠvalutare similarità  e differenze tra questi fiumi nell'ottica di un approccio di analisi a scala regionale, per contribuire al miglioramento della conoscenza sulle loro dinamiche interne e i loro legami con i principali fattori ambientali, fornendo utili informazioni per la gestione della conservazione di questi habitat fortemente minacciati. La prima parte del lavoro ਠincentrata sullo studio dei pattern di distribuzione delle specie ed ਠvolta ad esaminare differenze floristiche a scala regionale (tra regioni) e a scala locale (differenze tra fiumi della stessa regione), per chiarificare quali siano i principali gradienti della flora ripariale e quanto e come la biogeografia influenzi la distribuzione di specie vegetali lungo questi fiumi. Nonostante le molte similarità  floristiche tra le due aree, in tutte le analisi condotte ਠsempre emersa un'elevata eterogeneità  floristica. Inoltre, l'appartenenza a differenti regioni si configura come la principale variabile che influenza la flora di questi fiumi, confermando il ruolo prominente della geografia nel guidare la distribuzione delle specie vegetali a scala regionale. A scala locale, ਠinvece il gradiente longitudinale che risulta avere il maggior peso in tutti i fiumi indagati. Il gradiente laterale risulta avere un effetto rilevante solo in Toscana. Sulla base dei precedenti risultati, nella seconda parte del lavoro vengono analizzati in maniera pi๠approfondita il contingente di specie endemiche ed esotiche dei fumi sardi. Il metodo qui utilizzato permette di stabilire in maniera rapida priorità  di conservazione comparando modelli di distribuzione di queste specie lungo il corridoio fluviale. I trend di distribuzione di queste specie risultano seguire in generale il gradiente di decrescente naturalità / crescente impatto antropico verso il mare, ma lo studio evidenzia la presenza di differenti gradi di naturalità  tra i due fiumi in generale, nonostante la presenza di aree protette in entrambi. Le aree pi๠critiche sono state individuate nel medio corso dei fiumi, dove le endemiche coesistono con le aliene e soprattutto con un elevato impatto antropico nelle aree circostanti, e dove dovrebbero essere concentrati i futuri piani di conservazione.