Lorenzo Lazzaro

Soil and plant changing after invasion: the case of Acacia dealbata in a Mediterranean ecosystem.

Acacia dealbata Link (Fabaceae) is one of the most invasive species in the Mediterranean ecosystems of Europe, Africa and America, where it has been proved to exert strong effects on soil and plant communities. In Italy A. dealbata has been largely used for ornamental and forestry purpose and is nowadays spreading in several areas. The present study was addressed to evaluate the impacts on soil chemical properties, soil microbial communities and understory plant communities and to assess the relationships among these compartments after the invasion of A. dealbata in a typical Mediterranean shrubland. Towards these aims, a soil and vegetation sampling was performed in Elba Island where A. dealbata is invading the sclerophyllous native vegetation. Three levels of invasion status were differentiated according to the gradient from invaded, to transitional and non-invaded vegetation. Quantitative and qualitative alterations of soil chemical properties and microbial communities (i.e. bacterial and fungal communities) and above-ground understory plant communities were found. In particular, the invaded soils had lower pH values than both the non-invaded and transitional ones. High differences were detected for both the total N and the inorganic fraction (NH4(+) and NO3(-)) contents, which showed the ranking: invaded>transitional>non-invaded soils. TOC and C/N ratio showed respectively higher and lower values in invaded than in non-invaded soils. Total plant covers, species richness and diversity in both the non-invaded and transitional subplots were higher than those in the invaded ones. The contribution of the nitrophilous species was significantly different among the three invasion statuses, with a strong increase going from native to transitional and invaded subplots. All these data confirm that A. dealbata modifies several compartments of the invaded ecosystems, from soil chemical properties to soil and plant microbial communities determining strong changes in the local ecosystem processes.

Plant invasions on small Mediterranean islands: An overview

Abstract Biological invasions have become one of the main drivers of habitat degradation and a leading cause of biodiversity loss in island ecosystems worldwide. The spread of invasive species poses a particular environmental threat on the islands of the Mediterranean Basin, which are hot spots of biodiversity and contain rare habitats and endemic species, especially on small islands, which are highly vulnerable to biodiversity loss. Following a recent survey, in this paper we aim to provide an overview of the present-day non-native vascular flora of small Mediterranean islands based on a sample of 37 islands located in the middle of the Mediterranean Sea, off the coast of Italy. By comparing the current data with those gathered during a previous survey conducted in the same study area, we also aim to highlight the main changes that have occurred in non-native plant species diversity, establishment and distribution in recent years and to present a first general overview of the most prominent plant taxa in the island’s introduced flora, focusing on those most responsible for these changes and those that pose the greatest environmental threats. We recorded 203 non-native plant species, 147 of which have established on at least one of the islands investigated. Overall, we detected a sharp increase in the number of species, in their levels of establishment and in the extent of their distribution within the study area in recent years. This may be explained by the intensification of research on plant invasions, as well as to new introduction, escape, establishment and invasion events on the islands in recent decades. The most remarkable plants detected include acacias and succulents, two groups that appear to be emerging very rapidly and to be posing new threats to the conservation of the islands’ natural environment, especially the genus Carpobrotus, whose spread into natural habitats containing rare and endemic taxa is seriously threatening biodiversity on both a local and global scale. On the whole, our results show that the plant invasion phenomenon in the study area has in recent years intensified considerably. As this process seems likely to continue, we should expect more establishment events in the future and the further spread of species that are already present. This is of particular conservation concern on the islands investigated in this survey, which are rich in endemisms, but have been facing deep socio-economic and environmental transformations in these last decades as a consequence of the abandonment of traditional management practices and the development of tourism. Our study thus confirms that plant invasions on Mediterranean islands are a serious environmental problem that threatens biodiversity conservation not only in the Mediterranean biogeographic region, but also on the global scale, and highlights the need to further increase efforts aimed at preventing, controlling or mitigating the effects of plant invasions in island ecosystems.

A checklist of the alien flora of the Tuscan Archipelago (Italy)

Biological invasions represent one of the major threats to biodiversity. Their impact is considered to be even higher in the island ecosystems, especially in Mediterranean ones, which host a very high diversity. Moreover nowadays the global changes and the local changes in the socio-economic drivers of these island enhanced human impact on the insular biota, also leading to an increase in alien species introductions and in a shift in the introduction pathways. In this framework, checklists of alien species represent a valuable tool for monitor the invasion process at a local scale. Aim of this paper is to provide an updated Checklist of the alien flora of the Tuscan Archipelago, also reporting some important information such year of first and more recent record and invasion status for each island. Intense field surveys were made to verify the presence of the reported species and detect the presence of new arrivals. The Checklist includes a total of 141 taxa belonging to 101 genera in 49 families. 31 taxa are considered invasive, 62 naturalized and 48 casual. Most of the species were introduced for ornamental purpose, according to socio-economical changes which nowadays see the tourism as the main economic driver in the Archipelago.

Detailed Natura 2000 and CORINE Biotopes habitat maps of the island of Elba (Tuscan Archipelago, Italy)

The island of Elba (Tuscan Archipelago, Italy) Natura 2000 habitat map (1:25,000) and the CORINE Biotopes habitat map (1:25,000) were derived from the phytosociological map of Elba integrated with recent studies and field knowledge of the vegetation units. Conventional geographical information system queries were used to manage and select the spatial information. For each map polygon, the following attributes were assigned: (i) habitat typology and (ii) percentage cover of each habitat type. Where multiple habitat types were associated with the same polygon, the percentage cover of each habitat type was estimated. A total of 27 Natura 2000 habitat types and 58 CORINE Biotopes habitat types were identified, these being distributed in single and/or multiple typological units. Distribution and covers of the different habitat types are discussed. The usefulness of this kind of map for monitoring and managing conservation actions is discussed.

Plant recording across two centuries reveals dramatic changes in species diversity of a Mediterranean archipelago

Although islands are model systems for investigating assembly of biological communities, long-term changes in archipelago communities are not well understood because of the lack of reliable data. By using a vast amount of floristic data we assembled a dataset of the plant species occurring on 16 islands of the Tuscan Archipelago, Italy, across two periods, 1830–1950 and 1951–2015. We collected 10,892 occurrence records for 1,831 species. We found major changes in the island plant assemblages between the two periods, with native flora significantly decreasing (−10.7%) and alien flora doubling (+132.1%) in richness. The species–area relationships demonstrated the scale-dependence of the observed changes for native and alien species. The observed floristic changes were dependent on island area, with smaller islands displaying high variability in richness and compositional changes and larger islands having more stable species assemblages. The richness of species associated with open landscapes, that had been maintained for centuries by traditional practices, markedly reduced while the number of woody species, associated with afforestation processes and invasion by alien woody plants, significantly incresed. These results demonstrate the great power of floristic studies, often available in grey literature, for understanding long-term biotic changes in insular ecosystems.

Demographic and macro-morphological evidence for common reed dieback in central Italy

Background: Phragmites australis dieback syndrome, recently reported for the Mediterranean basin, features several symptomatic traits among which the clumping habit seems to be one of the most diagnostic. Aims: We evaluated the effect of water depth on the intensity of the clumping habit and evaluated the diagnostic role of other traits. Methods: We investigated patterns of macro-morphological (culm height and diameter, flowering head and dead apical bud rates) and demographic (density) traits of P. australis in function of submersion (PF-permanent vs. NF-temporary) at five Italian wetland sites. We related the occurrence of clumping and its frequency with water depth. Results: There were clear trends, modulated by site-specific effects, for most of the considered traits in function of the duration of submersion. The clumping rate was close to zero in NF-stands, reached high values in PF-stands and was positively correlated with water depth. Conclusions: We have shown that permanent submersion with deep water levels plays a crucial role in the occurrence of reed dieback. As all other considered traits, with the exception of the occurrence of dead apical buds, well correlate with the clumping habit, we propose using clumping as a key indicator for detecting potential reed dieback.

Predicting risk of invasion in a Mediterranean island using niche modelling and valuable biota

Abstract Invasion by alien species is nowadays considered as one of the major threats to biodiversity. Thus, the identification of the areas exposed to a greater risk of invasion represents a priority for management purpose, especially in presence of habitats worthy of conservation. This paper aims to propose a method to produce a map of risk of invasion, merging together the threat of invasion by invasive plants and the distribution of habitats with high conservation value, on the case study of the Island of Elba (Tuscan Archipelago). We modelled the potential distribution of six particularly harmful invasive plants and merged these distributions into a map of threat of invasion. This map was overlapped to the map of density of Natura2000 habitats, finally obtaining a map of risk of invasion. According to our analyses, the potential distribution of the invasive species resulted highly influenced by human-related factors. The habitats more at risk are those closer to streets and anthropic habitats, which are more likely to be colonized by the invasive species we studied. We identified some rare habitats which are strongly endangered, highlighting that around 20% of the surface of the Island is exposed to some level of risk of invasion.

Temperature-related effects on the germination capacity of black locust ( Robinia pseudoacacia L., Fabaceae) seeds

Germination is a key trait promoting species invasiveness and has become a major goal in invasion ecology. In this study, the effects of different scarification methods and temperature regimes on seed germination performance of the invasive exotic tree Robinia pseudoacacia L. were investigated. Ripe seeds were gathered from six collection sites in Tuscany (central Italy). Mechanical, chemical and thermal scarifications and no pretreatment were applied; seeds were incubated in a range (9–21°C) of constant temperature regimes. The scarification treatments proved highly important for the germination performance of seeds in term of both final response and germination rate in time, with mechanical scarification being the most effective treatment. Temperature significantly affected the germination rate and the mean germination time of the mechanically scarified seeds. The cumulative germination rate significantly decreased with the reduction of the temperature, with the highest value in the 18–21°C regimes (ca 98%), and the lowest in the 9–12°C regimes (ca 60%). The mean germination time slightly decreased with increasing temperature, but was substantially similar between 18°C and 21°C. Our data indicate that the temperature affected the onset of seed germination and that the lowest temperature tested delayed germination. These plastic germination responses, as well as the high germination capacity at lower temperature, may result in the spread of the propagule germination over a large time interval, contributing to the invasiveness of this species.

Plant species loss and community nestedness after leguminous tree Acacia pycnantha invasion in a Mediterranean ecosystem

Invasions of ecosystems by alien species are one of the major threats to biodiversity. Among alien plant species, members of the family Fabaceae s.l. represent some of the most dangerous and well known global invaders. In Mediterranean ecosystems, many Australian acacias have been found to establish and rapidly spread, often determining severe impacts on understorey vegetation. In the present work, we report a case study of an Acacia pycnantha invasion in a typical Mediterranean matorral (Elba Island, central Mediterranean Sea, Italy). We conducted a survey of understorey plant communities across an invasion gradient from non-invaded to transitional and invaded areas, aiming to quantify the impacts on the understorey assemblage and to investigate the ecological processes involved in the changes in species composition. The understorey plant community was highly affected starting from the intermediate stage of invasion. Species richness, diversity and total cover were all lower in invaded than in non-invaded plots, with a transition generally in the middle. In addition, plant community composition severely changed along the invasion gradient. The species set we recorded showed a nested structure, with the composition of species in the invaded plots representing a subset of the others. According to our findings, A. pycnantha exerted detrimental impacts on the native vegetation, mainly causing a severe species loss in the understorey assemblage and the impoverishment of the invaded ecosystems.

Impacts of Myriophyllum aquaticum invasion in a Mediterranean wetland on plant and macro-arthropod communities

Abstract The invasion by alien macrophytes in aquatic ecosystems may produce a strong alteration of the native aquatic vegetation leading to heavy impacts for both plant and faunal native diversity. Myriophyllum aquaticum is an aquatic plant native of Southern America, invasive in several part of the world. We studied the effects of M. aquaticum invasion on plant and macro-arthropod communities in the canals around a protected wetland in the Mediterranean basin. We sampled plant and macro-arthropod communities in 10 transects in invaded and non-invaded tracts of the canals. We assessed the differences in plant and macro-arthropod species richness, diversity, taxonomic diversity and species composition between invaded and non-invaded habitats by means of univariate and multivariate analyses. Our study shows a significant loss of plant diversity between non-invaded to invaded sites, leading to communities numerically and taxonomically impoverished and highly divergent in the species composition. We also detected significant differences in arthropod species composition between invaded and non-invaded transects. Some taxa such as mosquitoes and malacostraca were more frequent in the M. aquaticum-dominated stands. Furthermore, the study shows a positive relation between invaded habitats and juvenile individuals of the invasive alien crayfish Procambarus clarkii.