Laura Celesti-Grapow

Inventory of the non‐native flora of Italy

Abstract In this paper we present a comprehensive inventory of the non‐native vascular flora of Italy, which was produced within the project “A survey of the Italian non‐native flora”, funded by the Italian Ministry for the Environment. Previously published floristic accounts were the main source of information. Historical records were critically revised and integrated with recent literature, data from herbaria and some unpublished information, so as to obtain a complete, up‐to‐date catalogue of the non‐native vascular plant species that occur spontaneously in Italy. The inventory lists 1023 non‐native species and subspecies, which account for 13.4% of all the Italian flora. The Italian non‐native flora was divided, according to its residence time, into 103 archaeophytes and 920 neophytes. According to its current invasion status, it was classified into 437 casual (42.7% of all non‐native) and 524 established taxa, the latter being divided into 361 naturalized non‐invasive (35.3%) and 163 invasive taxa (15.9%). The inventory includes a group of 62 species (6.1%) that lack recent records (i.e. since 1950). By combining local expertise into a unified, nationwide scheme using a standardized method and terminology, the inventory provides the essential scientific basis for the development of plant invasion research and management in the country.

No saturation in the accumulation of alien species worldwide

Although research on human-mediated exchanges of species has substantially intensified during the last centuries, we know surprisingly little about temporal dynamics of alien species accumulations across regions and taxa. Using a novel database of 45,813 first records of 16,926 established alien species, we show that the annual rate of first records worldwide has increased during the last 200 years, with 37% of all first records reported most recently (1970–2014). Inter-continental and inter-taxonomic variation can be largely attributed to the diaspora of European settlers in the nineteenth century and to the acceleration in trade in the twentieth century. For all taxonomic groups, the increase in numbers of alien species does not show any sign of saturation and most taxa even show increases in the rate of first records over time. This highlights that past efforts to mitigate invasions have not been effective enough to keep up with increasing globalization.

Non‐native flora of Italy: Species distribution and threats

Abstract In this paper, we provide an overview of the distribution and invasive status of non‐native species in the Italian flora across its administrative regions, biogeographic regions and main land use types, and a synthesis of current knowledge on the threats they pose within the country. The information on non‐native plant species collected during the project “A survey of the non‐native Italian flora” was used to compile comprehensive regional and national databases. The number of non‐native species within a given administrative region increases in proportion to its size, resident population density and latitude, reaching the highest values in the intensively cultivated, heavily industrialized and urbanized Po Plain in northern Italy. The number of casual species is positively correlated with the number of yearly visitors in each region and negatively correlated with the proportion of mountainous terrain within the region. If compared with the Continental and Mediterranean biogeographic regions, the Alpine region yields the lowest number of non‐native species and lowest proportion of casual species. The number and density of introduced species is highest in artificial land use types, particularly in urban areas. A negative impact is reported to be exerted by 203 species, most of which are agricultural weeds.

Widespread plant species: natives versus aliens in our changing world

Estimates of the level of invasion for a region are traditionally based on relative numbers of native and alien species. However, alien species differ dramatically in the size of their invasive ranges. Here we present the first study to quantify the level of invasion for several regions of the world in terms of the most widely distributed plant species (natives vs. aliens). Aliens accounted for 51.3% of the 120 most widely distributed plant species in North America, 43.3% in New South Wales (Australia), 34.2% in Chile, 29.7% in Argentina, and 22.5% in the Republic of South Africa. However, Europe had only 1% of alien species among the most widespread species of the flora. Across regions, alien species relative to native species were either as well-distributed (10 comparisons) or more widely distributed (5 comparisons). These striking patterns highlight the profound contribution that widespread invasive alien plants make to floristic dominance patterns across different regions. Many of the most widespread species are alien plants, and, in particular, Europe and Asia appear as major contributors to the homogenization of the floras in the Americas. We recommend that spatial extent of invasion should be explicitly incorporated in assessments of invasibility, globalization, and risk assessments.

The Role of Alien and Native Weeds in the Deterioration of Archaeological Remains in Italy

Abstract Plants growing on ancient buildings and archaeological remains pose a severe threat to their conservation. Controlling such weeds is costly, and the use of herbicides may lead to serious ecological problems. We surveyed 20 archaeological sites in Mediterranean Italy and estimated the relative effect of alien and native weeds on archaeological remains on the basis of their abundance, frequency, and danger index (DI), which is a measure of the potential damage that each species can cause to buildings and remains. DI is assessed according to plant morphology, vigor, and life-form. The results show that, although alien plant species are potentially harmful, as revealed by their significantly higher DI, they rarely grow on remains, whereas native plants thrive. Despite human disturbance and abundant propagule supply, factors that generally enhance the establishment of aliens, the flora growing on archaeological remains was relatively resistant to alien invasion. Among the aliens observed, only tree-of-heaven turned out to be relatively harmful. Although this invasive tree is not frequent on remains, it is expected to become more widespread on them, as areas surrounding archaeological sites become increasingly urbanized. Nomenclature: Tree-of-heaven, Ailanthus altissima (Mill.) Swingle #3 AILAL. Additional index words: Biodeterioration, invasion resistance, Mediterranean Basin. Abbreviations: DI, danger index.

Determinants of non-native plant species richness and composition across small Mediterranean islands

The main aim of this paper is to assess the drivers of non-native plant species richness and composition on a set of 37 small Mediterranean islands in Italy. We compiled the list of the non-native flora and distinguished species according to their establishment status. The non-native flora of the islands studied consists of 154 species, 105 of which are established on at least one island. Regression tree analysis revealed that the main determinants of both total non-native and established non-native species richness are the variables linked to tourist development and the sprawl of artificial surfaces. The variation partitioning approach shows that the variation in total non-native flora composition is driven above all by environmental variables, whereas when established taxa are considered, human-mediated factors account for most of the explained variation. Mediterranean islands have recently experienced changes in the type and intensity of human activities, leading to a decline in rural landscape and the development of tourist facilities. Our results indicate that tourism and the increase in the extension of artificial surfaces are also the main drivers of non-native plant species occurrence and establishment. These factors outweigh the effects of abiotic variables such as climate and lithology in determining the number of non-native species, whether it be total or established, as well as variations in the composition of established species. High human pressure and ornamental introductions associated with tourist activities appear to be the key elements that need to be considered when planning strategies aimed at managing plant invasions in Mediterranean islands.

Exploring taxonomic filtering in urban environments

Abstract Question: Several mechanisms have been proposed that control the spatio-temporal pattern of species coexistence. Among others, the species pool hypothesis states that the large-scale species pool is an important factor in controlling small-scale species richness through filtering of species that can persist within a species assemblage on the basis of their tolerance of the abiotic environment. Because of the process of environmental filtering, co-occurring species that experience similar environmental conditions are likely to be more taxonomically similar than ecologically distant species. This is because, due to the conservatism of many species traits during evolutionary diversification, the ability of species to colonize the same ecological space is thought to depend at least partially on their taxonomic similarity. The question for this study is: Under the assumption of trait conservatism, does environmental filtering lead to nonrandom species assemblages with respect to their taxonomic structure? Methods: The significance of taxonomic filtering in regulating species coexistence is tested using data from 15 local species assemblages from the urban flora of Rome (Italy). To find out whether the taxonomic structure of the selected ‘local’ species assemblages was significantly different from random, we used a Monte Carlo simulation in which for each local species assemblage, the actual taxonomic diversity was compared to the taxonomic diversity of 1000 virtual species lists of the same size extracted at random from a larger ‘regional’ species pool. Results: We found that in most cases the local species assemblages have a higher degree of taxonomic similarity than would be expected by chance showing a phenomenon of ‘species condensation’ in a small number of higher-level taxa. Conclusions: Our observations support the species pool hypothesis and imply that environmental filtering is an important mechanism in shaping the taxonomic structure of species assemblages. Therefore, the incorporation of taxonomic diversity into landscape and community ecology may be beneficial for a better understanding of the processes that regulate species coexistence. Nomenclature: Conti et al. 2005.

Comparative patterns of plant invasions in the mediterranean biome

The objective of this work was to compare and contrast the patterns of alien plant invasions in the world’s five mediterranean-climate regions (MCRs). We expected landscape age and disturbance history to have bearing on levels of invasion. We assembled a database on naturalized alien plant taxa occurring in natural and semi-natural terrestrial habitats of all five regions (specifically Spain, Italy, Greece and Cyprus from the Mediterranean Basin, California, central Chile, the Cape Region of South Africa and Southwestern - SW Australia). We used multivariate (hierarchical clustering and NMDS ordination) trait and habitat analysis to compare characteristics of regions, taxa and habitats across the mediterranean biome. Our database included 1627 naturalized species with an overall low taxonomic similarity among the five MCRs. Herbaceous perennials were the most frequent taxa, with SW Australia exhibiting both the highest numbers of naturalized species and the highest taxonomic similarity (homogenization) among habitats, and the Mediterranean Basin the lowest. Low stress and highly disturbed habitats had the highest frequency of invasion and homogenization in all regions, and high natural stress habitats the lowest, while taxonomic similarity was higher among different habitats in each region than among regions. Our analysis is the first to describe patterns of species characteristics and habitat vulnerability for a single biome. We have shown that a broad niche (i.e. more than one habitat) is typical of naturalized plant species, regardless of their geographical area of origin, leading to potential for high homogenization within each region. Habitats of the Mediterranean Basin are apparently the most resistant to plant invasion, possibly because their landscapes are generally of relatively recent origin, but with a more gradual exposure to human intervention over a longer period.

Geographical Constraints Are Stronger than Invasion Patterns for European Urban Floras

Understanding the mechanisms that affect invasion success of alien species is an important prerequisite for the effective management of present and future aliens. To gain insight into this matter we asked the following questions: Are the geographical patterns of species distributions in urban floras different for native compared with alien plant species? Does the introduction of alien species contribute to the homogenization of urban floras? We used a Mantel test on Jaccard dissimilarity matrices of 30 urban floras across the British Isles, Italy and central Europe to compare the spatial distribution of native species with four classes of alien species: archaeophytes, all neophytes, non-invasive neophytes, and invasive neophytes. Archaeophytes and neophytes are species that were introduced into Europe before and after 1500 AD, respectively. To analyze the homogenizing effect of alien species on the native urban floras, we tested for differences in the average dissimilarity of individual cities from their group centroid in ordination space. Our results show that the compositional patterns of native and alien species seem to respond to the same environmental drivers, such that all four classes of alien species were significantly related to native species across urban floras. In this framework, alien species may have an impact on biogeographic patterns of urban floras in ways that reflect their history of introduction and expansion: archaeophytes and invasive neophytes tended to homogenize, while non-invasive neophytes tended to differentiate urban floras.

The silent invasion of Eichhornia crassipes (Mart.) Solms. in Italy

This article provides general information and original data on the period of first introduction in Europe (1823–1825) and in Italy (first half of the 19th century), and on the current distribution and impacts in Italy of the invasive macrophyte Eichhornia crassipes. Two main pathways are responsible for the presence of this species in Italy: (i) introduction as an ornamental and (ii) research and use for phytoremediation. After a time lag of more than 100 years, E. crassipes has recently started invading the Italian freshwaters. A specific action plan for this species is required, including local eradication and awareness campaigns. Furthermore, regulations in the trade sector of invasive aquatic plant species need to be introduced and the possibilities for biological or integrated control evaluated.