Plant invasion in Mediterranean Europe: current hotspots and future scenarios

The Mediterranean Basin has historically been subject to alien plant invasions that threaten its unique biodiversity. This seasonally dry and densely populated region is undergoing severe climatic and socioeconomic changes, and it is unclear whether these changes will worsen or mitigate plant invasions. Predictions are often biased, as species may not be in equilibrium in the invaded environment, depending on their invasion stage and ecological characteristics. To address future predictions uncertainty, we identified invasion hotspots across multiple biased modelling scenarios and ecological characteristics of successful invaders. We selected 92 alien plant species widespread in Mediterranean Europe and compiled data on their distribution in the Mediterranean and worldwide. We combined these data with environmental and propagule pressure variables to model global and regional species niches, and map their current and future habitat suitability. We identified invasion hotspots, examined their potential future shifts, and compared the results of different modelling strategies. Finally, we generalised our findings by using linear models to determine the traits and biogeographic features of invaders most likely to benefit from global change. Currently, invasion hotspots are found near ports and coastlines throughout Mediterranean Europe. However, many species occupy only a small portion of the environmental conditions to which they are preadapted, suggesting that their invasion is still an ongoing process. Future conditions will lead to declines in many currently widespread aliens, which will tend to move to higher elevations and latitudes. Our trait models indicate that future climates will generally favour species with conservative ecological strategies that can cope with reduced water availability, such as those with short stature and low specific leaf area. Taken together, our results suggest that in future environments, these conservative aliens will move farther from the introduction areas and upslope, threatening mountain ecosystems that have been spared from invasions so far

Shedding light on typical species : implications for habitat monitoring

Habitat monitoring in Europe is regulated by Article 17 of the Habitats Directive, which suggests the use of typical species to assess habitat conservation status. Yet, the Directive uses the term “typical” species but does not provide a definition, either for its use in reporting or for its use in impact assessments. To address the issue, an online workshop was organized by the Italian Society for Vegetation Science (SISV) to shed light on the diversity of perspectives regarding the different concepts of typical species, and to discuss the possible implications for habitat monitoring. To this aim, we inquired 73 people with a very different degree of expertise in the field of vegetation science by means of a tailored survey composed of six questions. We analysed the data using Pearson's Chi-squared test to verify that the answers diverged from a random distribution and checked the effect of the degree of experience of the surveyees on the results. We found that most of the surveyees agreed on the use of the phytosociological method for habitat monitoring and of the diagnostic and characteristic species to evaluate the structural and functional conservation status of habitats. With this contribution, we shed light on the meaning of “typical” species in the context of habitat monitoring

Invasion success on European coastal dunes

Many invasive plants are threatening the already highly vulnerable habitats of coastal dunes in Europe. Setting priority target species to control is mandatory for an effective planning of invasion management strategies at European level. This can be possible after identifying the species that currently have greater invasion success, in consideration of their ecological traits and origin. We quantified the three main components of invasion success for the extra-European alien plants found on European coastal dunes: local abundance, regional distribution and niche breadth, and related them to their life forms and origins. We found that life form was a better predictor of invasion success. In particular, geophytes and therophytes were the species with the greatest invasion success. Quite surprisingly, alien plants from Africa appeared as the group with slightly higher mean invasion success although this result was no statistically significant. We also highlighted the species deserving special attention. Among these, Xanthium orientale, Erigeron canadensis and Oenothera gr. biennis showed the widest levels of niche breadth and regional distribution, and had overall the greatest invasion success, but other species also had high levels in one of the three components of invasion success

Exploring temporal trends of plant invasion in mediterranean coastal dunes

© 2021 by the authors.Alien plants represent a significant threat to species diversity and composition in natural habitats. Nevertheless, little is known about the dynamic of the invasion process and how its effects on native species change over time. In this study, we explored vegetation changes that occurred in invaded coastal dune habitats over the last 10–15 years (2005–2020), particularly addressing impacts on alien and diagnostic species. To monitor temporal trends, we used data resulting from a revisitation study. After detecting overall changes in alien species occurrence and cover over time, 127 total plots were grouped into plots experiencing colonization, loss, or persistence of alien species. For these three categories, we compared historical and resurveyed plots to quantify changes in native species composition (using the Jaccard dissimilarity index) and to measure variations in diagnostic species cover. The number of alien species doubled over time (from 6 to 12) and two species, Yucca gloriosa and Agave americana, strongly increased their cover (+5.3% and +11.4%, respectively). Furthermore, plots newly invaded appeared to record the greatest changes in both native and diagnostic species. Our results suggest the need for regular monitoring actions to better understand invasion processes over time and to implement effective management strategies in invaded coastal dune habitats

Exploring Temporal Trends of Plant Invasion in Mediterranean Coastal Dunes

Alien plants represent a significant threat to species diversity and composition in natural habitats. Nevertheless, little is known about the dynamic of the invasion process and how its effects on native species change over time. In this study, we explored vegetation changes that occurred in invaded coastal dune habitats over the last 10–15 years (2005–2020), particularly addressing impacts on alien and diagnostic species. To monitor temporal trends, we used data resulting from a revisitation study. After detecting overall changes in alien species occurrence and cover over time, 127 total plots were grouped into plots experiencing colonization, loss, or persistence of alien species. For these three categories, we compared historical and resurveyed plots to quantify changes in native species composition (using the Jaccard dissimilarity index) and to measure variations in diagnostic species cover. The number of alien species doubled over time (from 6 to 12) and two species, Yucca gloriosa and Agave americana, strongly increased their cover (+5.3% and +11.4%, respectively). Furthermore, plots newly invaded appeared to record the greatest changes in both native and diagnostic species. Our results suggest the need for regular monitoring actions to better understand invasion processes over time and to implement effective management strategies in invaded coastal dune habitats

Exploring Temporal Trends of Plant Invasion in Mediterranean Coastal Dunes

Alien plants represent a significant threat to species diversity and composition in natural habitats. Nevertheless, little is known about the dynamic of the invasion process and how its effects on native species change over time. In this study, we explored vegetation changes that occurred in invaded coastal dune habitats over the last 10–15 years (2005–2020), particularly addressing impacts on alien and diagnostic species. To monitor temporal trends, we used data resulting from a revisitation study. After detecting overall changes in alien species occurrence and cover over time, 127 total plots were grouped into plots experiencing colonization, loss, or persistence of alien species. For these three categories, we compared historical and resurveyed plots to quantify changes in native species composition (using the Jaccard dissimilarity index) and to measure variations in diagnostic species cover. The number of alien species doubled over time (from 6 to 12) and two species, Yucca gloriosa and Agave americana, strongly increased their cover (+5.3% and +11.4%, respectively). Furthermore, plots newly invaded appeared to record the greatest changes in both native and diagnostic species. Our results suggest the need for regular monitoring actions to better understand invasion processes over time and to implement effective management strategies in invaded coastal dune habitats

The biogeography of alien plant invasions in the Mediterranean Basin

Aims Humans have deeply eroded biogeographic barriers, causing a rapid spread of alien species across biomes. The Mediterranean Basin is a biodiversity hotspot but is also known as a hub of alien plant invasions, particularly in its European part. Yet, a comprehensive inventory of alien species in the area is missing and understanding of the drivers of Mediterranean invasions is poor. Here, we aim to identify the main alien plant species in the European part of the Mediterranean Basin and quantify their invasion success in order to understand the plant species flows from other biomes of the world. Location The Mediterranean region of Europe, Anatolia and Cyprus. Methods We analyzed 130,000 georeferenced vegetation plots from the European Vegetation Archive (EVA) and identified 299 extra-European alien plant species. We identified their biomes of origin and quantified the mean geographic distance, trade exchange and climatic similarity from each biome to the study area. After estimating the invasion success of each species in the study area, we tested which biomes have donated more alien species than expected by chance and which drivers best explain these non-random patterns. Results We found that other Mediterranean climatic regions, as well as temperate and xeric biomes of the world, are the main donors of successful alien species to Mediterranean Europe, beyond what would be expected by chance. Our results suggest that climatic matching, rather than geographic proximity or trade, has been the most important driver of invasion. However, climatic pre-adaptation alone also does not appear to predict the invasion success of established species in the study area. Conclusions Our results highlight the need to pay special attention to alien plant species from the same or climatically similar biomes, but also suggest that further research is needed for early screening of the most problematic alien species

The biogeography of alien plant invasions in the Mediterranean Basin

Aims Humans have deeply eroded biogeographic barriers, causing a rapid spread of alien species across biomes. The Mediterranean Basin is a biodiversity hotspot but is also known as a hub of alien plant invasions, particularly in its European part. Yet, a comprehensive inventory of alien species in the area is missing and understanding of the drivers of Mediterranean invasions is poor. Here, we aim to identify the main alien plant species in the European part of the Mediterranean Basin and quantify their invasion success in order to understand the plant species flows from other biomes of the world. Location The Mediterranean region of Europe, Anatolia and Cyprus. Methods We analyzed 130,000 georeferenced vegetation plots from the European Vegetation Archive (EVA) and identified 299 extra-European alien plant species. We identified their biomes of origin and quantified the mean geographic distance, trade exchange and climatic similarity from each biome to the study area. After estimating the invasion success of each species in the study area, we tested which biomes have donated more alien species than expected by chance and which drivers best explain these non-random patterns. Results We found that other Mediterranean climatic regions, as well as temperate and xeric biomes of the world, are the main donors of successful alien species to Mediterranean Europe, beyond what would be expected by chance. Our results suggest that climatic matching, rather than geographic proximity or trade, has been the most important driver of invasion. However, climatic pre-adaptation alone also does not appear to predict the invasion success of established species in the study area. Conclusions Our results highlight the need to pay special attention to alien plant species from the same or climatically similar biomes, but also suggest that further research is needed for early screening of the most problematic alien species