Corresponding author: Silvia Giulio ( silvia.giulio@uniroma3.it ) Academic editor: Daniele Viciani
© 2021 Silvia Giulio, Luigi Cao Pinna, Marta Carboni, Flavio Marzialetti, Alicia Teresa Rosario Acosta.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Giulio S, Cao Pinna L, Carboni M, Marzialetti F, Acosta ATR (2021) Invasion success on European coastal dunes. Plant Sociology 58(1): 29-39. https://doi.org/10.3897/pls2021581/02
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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.
alien plants, coastal vegetation, ecological success, generalist species, local abundance, niche breadth, regional distribution, sand dunes
The repeated introduction of alien species is a major component of ongoing global changes and a major threat to global biodiversity (
As effective invasion management strategies cannot possibly consider the large number of invasive plants currently present on European coastal dunes, a more realistic approach would be to focus management efforts on those aliens which have greater invasion success. The ecological success of introduced species depends on their biological traits, on the pressure of introduced propagules and on local ecosystem invasibility (
Different studies have highlighted the importance of life forms and geographical species origin as factors related to invasion success (
Similarly, considering the geographic origin of successful invasive plants may allow to tune prevention strategies to avoid further introductions. Geographic origin of invasive species depends on different factors (
In a previous study,
Our study focuses on the two most characteristic and dynamic habitat types in the coastal dune vegetation zonation (
An initial dataset of 23,446 georeferenced vegetation plots (relevés) containing 2,035 vascular plant species with cover values was extracted from EVA (
We applied the Rabinowitz’s classification of rarity and abundance (
(1) Local abundance was taken from the average percentage cover of each alien species within the plots where it occurred. To calculate it, we first converted the Braun-Blanquet cover classes to cover percentages using the median value of the corresponding class of cover percentage, then we calculated the mean for each species.
(2) to quantify the regional distribution of each alien plant in the study area, we calculated the species’ frequency of occurrence. To calculate it, we counted the number of plots where each alien species occurred. Because few species had an extremely high number of occurrences compared to most, we performed a logarithmic transformation. This measure was strongly correlated with geographical spread (calculated as a multiplication between the latitudinal and the longitudinal range to approximate the area of a rectangular polygon encompassing all occurrence points).
(3) To calculate the niche breadth, we extracted, for each alien plant location, the value of two climatic variables, annual temperature and annual precipitation, at a spatial resolution of ̴1 km (
We also used these three indices to calculate a synthetic index of success through a PCA (Fig.
Finally, we performed a Kruskal-Wallis test for non-parametric distributions to check if there was an effect of alien species’ life forms and origins on the invasion success’ components, followed by a pairwise comparison test with Bonferroni correction between life forms and origins to identify significantly different pairs. All analyses were performed in the R software (
Principal component analysis performed to calculate the synthetic index of invasion success. The scatterplot of alien species is distributed in relation to the three vectors representing the three components of invasion success projected along the first and second components. Ch = chamephyte; G = geophyte; H = Hemicryptophyte; P = phanerophyte; T = therophyte; more than one = species able to exist under more than one life form. Africa = species from Africa (excluding Northern Africa); America C/S = species from Central or South America; America N = species from North America; Eastern Asia = species from Eastern Asia (for example from India, China or Japan); Oceania = species from Australia and surrounding regions. Correlation matrix between variables and axis are showed in appendix S1 of Supporting information.
The Kruskal-Wallis test highlighted that life forms had a statistically significant effect on local abundance, on regional distribution, and on the general invasion success, but not on niche breadth (Table
The species which showed the greatest invasion success was Xanthium orientale, followed by Erigeron canadensis and Oenothera gr. biennis (Appendix II). All these three species had very wide niche breadth and regional distribution, but low local abundance. The species with the widest niche breadth was Gomphocarpus fruticosus. Other species with wide niche breath were Amorpha fruticosa, Ambrosia artemisiifolia and Helianthus annuus, while other species with wide regional distribution were Carpobrotus spp. and Xanthium strumarium. Carpobrotus also had intermediate levels of local abundance and niche breadth, and Xanthium strumarium wide niche breadth. The other species with high invasion success had wide niche breadth, intermediate levels of regional distribution, and in some cases also intermediate levels of local abundance, such as Senecio inaequidens, Oenothera drummondii and Oenothera glazioviana. The species with greatest local abundance were Lepidium densiflorum, Amsinckia menziesii, Populus trichocarpa, Pseudognaphalium undulatum and Solanum tuberosum, but these occurred in no more than one plot across the study area. Arctotheca calendula had both very high local abundance and wide niche breadth, while Paspalum vaginatum high local abundance and an intermediate level of regional distribution. Also Lupinus arboreus and Epilobium brunnescens had high local abundance, but low levels of the other components. Ambrosia psilostachya had instead intermediate levels in all the three components.
Violin plots of the three components of ecological success related to (a) life forms and (b) species’ origins. Values were rescaled between 0 and 1 (by subtracting the minimum and dividing by the range) for comparability. Bold segment shows the mean and fine segments the quantiles. Asterisks highlight the groups with significantly higher values than other groups according to pairwise Wilcoxon test with Bonferroni correction (Local abundance of G > P, p-value = 0.026; G > T, p-value = 0.041; Regional distribution of G > P, p-value = 0.024). Oceanian origin and chamaephyte group were not represented in these graphs because they included a small number of species (respectively only one and three species). G = geophytes, H = hemicryptophytes, P = phanerophytes, T = therophytes.
Kruskal-Wallis chi-squared tests of the effect of life form and origin on each component of invasion success.
Kruskal-Wallis chi-squared test | Degrees of freedom | p-value | |
Life form | |||
Local abundance | 12.35 | 3 | 0.006 |
Regional distribution | 9.06 | 3 | 0.029 |
Niche breadth | 4.93 | 3 | 0.177 |
Invasion success | 8.10 | 3 | 0.044 |
Origin | |||
Local abundance | 3.79 | 3 | 0.285 |
Regional distribution | 2.56 | 3 | 0.465 |
Niche breadth | 2.45 | 3 | 0.484 |
Invasion success | 3.90 | 3 | 0.273 |
Synthetic index of invasion success, related to (a) life forms and (b) species’ origins. Values are the normalized first component's scores. Bold segment shows the mean and the other segments the quantiles. Oceanian origin and Chamaephyte group were not represented in these graphs because they included a small number of species (respectively only one and three species). G = geophytes, H = hemicryptophytes, P = phanerophytes, T = therophytes.
In this study we quantified for the first time the main components of invasion success for alien plants from outside of Europe found on European coastal dunes. We observed that geophytes and therophytes were the species with the greatest invasion success, and African alien species were the group with slightly higher mean success. However, many of the alien plants with the highest invasion success were also of North American origin.
Life form confirmed to be a highly informative ecological trait in the coastal environment (
Alien plants from Africa did include more species with high local abundance and consequently this was the group with slightly higher mean invasion success. However, we should note that the relationship between geographic origins and the invasion success of alien plants was not statistically significant. This result confirmed those of
The plants with the highest invasion success level (Xanthium orientale, Erigeron canadensis and Oenothera gr. biennis) are all ruderal therophytes or hemicryptophytes from North America. Their invasion has been related to human disturbance (
Overall, the present work provides useful information for keeping track of the alien species which have most invasion success on coastal dunes which is a key issue in European invasion management strategies. Our list of successful alien species could be particularly valuable to plan prioritising management targets, from regional to local scales. Management planning should target first the most successful invaders and monitor emerging invasions (
Species with most invasion success. Values are scaled between 0 and 1. Ch = chamephyte, G = geophyte, H = hemicryptophyte, P = phanerophyte, T = therophyte. Bold corresponds to higher values of niche breadth, local abundance and regional distribution. The complete list of aliens and their invasion success’ values is in Appendix II.
Species | Origin | Life form | Local abundance | Regional distribution | Niche breadth | Invasion success |
Xanthium orientale L. | America N | T | 0.30 | 1.00 | 0.75 | 1.00 |
Erigeron canadensis L. | America C | T | 0.24 | 0.90 | 0.90 | 0.99 |
Oenothera gr. biennis L. | America N | H | 0.36 | 0.85 | 0.78 | 0.93 |
Carpobrotus N.E.Br. spp. | Africa | Ch | 0.55 | 0.81 | 0.57 | 0.82 |
Xanthium strumarium L. | America S | T | 0.14 | 0.79 | 0.71 | 0.82 |
Amorpha fruticosa L. | America N | P | 0.16 | 0.56 | 0.94 | 0.78 |
Ambrosia artemisiifolia L. | America N | T | 0.08 | 0.56 | 0.94 | 0.78 |
Senecio inaequidens DC | Africa | Ch / T | 0.53 | 0.58 | 0.74 | 0.75 |
Oenothera drummondii Hook. | America N | H | 0.44 | 0.52 | 0.75 | 0.71 |
Oenothera glazioviana Micheli | America N | H | 0.45 | 0.45 | 0.85 | 0.71 |
Oenothera parviflora L. | America N | H | 0.18 | 0.48 | 0.87 | 0.71 |
Arctotheca calendula L. | Africa | T | 0.98 | 0.36 | 0.81 | 0.70 |
Cuscuta campestris Yunck | America C | T | 0.21 | 0.48 | 0.77 | 0.67 |
Prunus serotina Ehrh. | America N | P | 0.00 | 0.52 | 0.72 | 0.65 |
Ambrosia psilostachya DC | America N | G | 0.65 | 0.60 | 0.41 | 0.64 |
Rosa rugosa Thunb. | Eastern Asia | P | 0.08 | 0.51 | 0.66 | 0.62 |
Helianthus annuus L. | America N | T | 0.06 | 0.29 | 0.94 | 0.60 |
Acosta ATR was supported by the Grant of Excellence Departments, MIUR Italy (article 1, subsection 314–337, law 232/2016), Carboni M by a Rita Levi Montalcini Grant, MIUR Italy, Giulio S and Cao Pinna L by PhD fellowship of Roma Tre University, and Marzialetti F by PhD fellowship of University of Molise.
We acknowledge the custodians and deputy custodians of the EVA project, who provided data to make this work possible (Corrado Marcenò, Maike Isermann, John Rodwell, Jan Pergl, Petr Pyšek, Juan Antonio Campos, Javier Loidi, Mercedes Herreira, John A. M. Janssen, Joop H. J. Schaminée, Zygmunt Kącki). We also acknowledge the Grant of Excellence Departments, MIUR-Italy (ARTICOLO 1, COMMI 314 – 337 LEGGE 232/2016).
Values of local abundance, regional distribution, niche breadth and invasion success, ranked from the most to the least successful species. Values are scaled between 0 and 1. Ch = chamaephyte, G = geophyte, H = hemicryptophyte, P = phanerophyte, T = therophyte.
Species | Origin | Life form | Local abundance | Regional distribution | Niche breadth | Invasion success |
Xanthium orientale L. | America N | T | 0.30 | 1.00 | 0.75 | 1.00 |
Erigeron canadensis L. | America C | T | 0.24 | 0.90 | 0.90 | 0.99 |
Oenothera gr. biennis L. | America N | H | 0.36 | 0.85 | 0.78 | 0.93 |
Carpobrotus N.E.Br. spp. | Africa | Ch | 0.55 | 0.81 | 0.57 | 0.82 |
Xanthium strumarium L. | America S | T | 0.14 | 0.79 | 0.71 | 0.82 |
Amorpha fruticosa L. | America N | P | 0.16 | 0.56 | 0.94 | 0.78 |
Ambrosia artemisiifolia L. | America N | T | 0.08 | 0.56 | 0.94 | 0.78 |
Senecio inaequidens DC | Africa | Ch / T | 0.53 | 0.58 | 0.74 | 0.75 |
Oenothera drummondii Hook. | America N | H | 0.44 | 0.52 | 0.75 | 0.71 |
Oenothera glazioviana Micheli | America N | H | 0.45 | 0.45 | 0.85 | 0.71 |
Oenothera parviflora L. | America N | H | 0.18 | 0.48 | 0.87 | 0.71 |
Arctotheca calendula L. | Africa | T | 0.98 | 0.36 | 0.81 | 0.70 |
Cuscuta campestris Yunck | America C | T | 0.21 | 0.48 | 0.77 | 0.67 |
Prunus serotina Ehrh. | America N | P | 0.00 | 0.52 | 0.72 | 0.65 |
Ambrosia psilostachya DC | America N | G | 0.65 | 0.60 | 0.41 | 0.64 |
Rosa rugosa Thunb. | Eastern Asia | P | 0.08 | 0.51 | 0.66 | 0.62 |
Helianthus annuus L. | America N | T | 0.06 | 0.29 | 0.94 | 0.60 |
Stenotaphrum secundatum (Walt.) | America C | G | 0.60 | 0.56 | 0.39 | 0.60 |
Cenchrus spinifex Cav. | America C | T | 0.21 | 0.53 | 0.54 | 0.60 |
Xanthium spinosum L. | America S | T | 0.34 | 0.54 | 0.39 | 0.55 |
Gomphocarpus fruticosus (L.) R. Br. | Africa | P | 0.00 | 0.17 | 1.00 | 0.54 |
Matricaria discoidea DC | America N | T | 0.18 | 0.35 | 0.68 | 0.54 |
Digitaria ciliaris (Retz.) Koeler | Eastern Asia | T | 0.18 | 0.46 | 0.46 | 0.51 |
Symphyotrichum subulatum (Spreng.) G.L. Nesom | America N | T | 0.00 | 0.31 | 0.68 | 0.50 |
Amaranthus retroflexus L. | America N | T | 0.00 | 0.24 | 0.77 | 0.49 |
Xanthium pungens Wallr. | America N | T | 0.00 | 0.24 | 0.75 | 0.48 |
Paspalum vaginatum Sw. | Africa | G | 0.88 | 0.44 | 0.22 | 0.48 |
Oenothera oakesiana (A. Gray) J.W. Robbins ex S. Watson. | America N | H | 0.31 | 0.61 | 0.08 | 0.46 |
Erigeron bonariensis L. | America S | T | 0.00 | 0.29 | 0.60 | 0.45 |
Hydrocotyle bonariensis Lam. | America C | G | 0.68 | 0.35 | 0.32 | 0.44 |
Erigeron floribundus (Kunth) Sch. Bip. | America S | T | 0.53 | 0.43 | 0.23 | 0.43 |
Lupinus arboreus Sims | America N | H | 0.88 | 0.37 | 0.21 | 0.43 |
Vitis rotundifolia Michx. | America C | P | 0.62 | 0.35 | 0.30 | 0.43 |
Solanum triflorum Nutt. | America N | T | 0.34 | 0.35 | 0.35 | 0.42 |
Spartina anglica (C.E.Hubb.) P.M.Peterson & Saarela | America N | G | 0.13 | 0.27 | 0.50 | 0.41 |
Cenchrus longispinus (Hack.) Fernald | America N | T | 0.40 | 0.46 | 0.14 | 0.40 |
Heterotheca subaxillaris (Lam.) Britton & Rusby | America N | H | 0.53 | 0.44 | 0.11 | 0.39 |
Claytonia perfoliata Donn ex Willd. | America N | T | 0.27 | 0.44 | 0.18 | 0.39 |
Yucca gloriosa L. | America N | P | 0.67 | 0.27 | 0.25 | 0.36 |
Amaranthus albus L. | America N | T | 0.00 | 0.10 | 0.67 | 0.36 |
Oenothera fallax Soldano & Rostański | America N | H | 0.52 | 0.45 | 0.01 | 0.35 |
Agave americana L. | America C | P | 0.25 | 0.21 | 0.43 | 0.35 |
Erigeron sumatrensis Retz. | America S | T | 0.00 | 0.21 | 0.50 | 0.35 |
Robinia pseudoacacia L. | America N | P | 0.00 | 0.10 | 0.62 | 0.34 |
Lycium barbarum L. | Eastern Asia | P | 0.50 | 0.10 | 0.45 | 0.32 |
Oxalis pescaprae L. | Africa | G | 0.38 | 0.33 | 0.11 | 0.30 |
Oenothera suaveolens Desf. ex Pers. | America N | H | 0.40 | 0.40 | 0.00 | 0.30 |
Sporobolus indicus (L.) R. Br. | America C | H | 0.60 | 0.24 | 0.17 | 0.30 |
Epilobium ciliatum Raf. | America N | H | 0.00 | 0.17 | 0.41 | 0.28 |
Oenothera ammophila Focke | America N | H | 0.36 | 0.36 | 0.00 | 0.27 |
Ambrosia tenuifolia Spreng. | America S | G | 0.67 | 0.27 | 0.00 | 0.25 |
Cortaderia selloana (Schult. & Schult. f.) Asch. & Graebn. | America S | H | 0.00 | 0.17 | 0.33 | 0.25 |
Epilobium brunnescens (Cockayne) P. H. Raven & Engelhorn | Oceania | H | 0.75 | 0.21 | 0.01 | 0.23 |
Populus balsamifera L. | America N | P | 0.00 | 0.29 | 0.00 | 0.19 |
Oenothera longiflora L. | America S | H | 0.20 | 0.24 | 0.00 | 0.18 |
Elaeagnus commutata Bernh. ex Rydb. | America N | P | 0.00 | 0.24 | 0.00 | 0.15 |
Solanum linnaeanum Hepper & P.-M.L. Jaeger | Africa | P | 0.00 | 0.17 | 0.10 | 0.15 |
Cycloloma atriplicifolium (Spreng.) J.M. Coult. | America N | T | 0.00 | 0.21 | 0.00 | 0.13 |
Lepidium densiflorum Schrad. | America N | H | 1.00 | 0.00 | 0.00 | 0.12 |
Amsinckia menziesii (Lehm.) A. Nelson & J.F. Macbr. | America N | P | 1.00 | 0.00 | 0.00 | 0.12 |
Populus trichocarpa Torr. & A.Gray ex. Hook. | America N | P | 1.00 | 0.00 | 0.00 | 0.12 |
Pseudognaphalium undulatum L. | Africa | T | 1.00 | 0.00 | 0.00 | 0.12 |
Solanum tuberosum L. | America S | T | 1.00 | 0.00 | 0.00 | 0.12 |
Juncus tenuis Willd. | America N | H | 0.00 | 0.17 | 0.00 | 0.10 |
Tetragonia tetragonoides (Pall.) Kuntze | Eastern Asia | T | 0.20 | 0.10 | 0.00 | 0.09 |
Suaeda foliosa Moq. | America S | Ch | 0.00 | 0.10 | 0.04 | 0.09 |
Vaccinium macrocarpon Ait. | America N | P | 0.00 | 0.10 | 0.01 | 0.07 |
Hypericum canadense L. | America N | P | 0.00 | 0.10 | 0.00 | 0.07 |
Heliotropium curassavicum L. | America C | Ch | 0.00 | 0.10 | 0.00 | 0.07 |
Symphyotrichum novibelgii (L.) G.L. Nesom | America N | H | 0.00 | 0.10 | 0.00 | 0.07 |
Aloe maculata All. | Africa | P | 0.00 | 0.10 | 0.00 | 0.07 |
Symphoricarpos albus (L.) S.F. Blake | America N | P | 0.00 | 0.10 | 0.00 | 0.07 |
Setaria italica (L.) P. Beauv. | Eastern Asia | T | 0.00 | 0.10 | 0.00 | 0.07 |
Solidago canadensis L. | America N | H | 0.40 | 0.00 | 0.00 | 0.05 |
Oenothera rubricaulis Kleb. | America N | H | 0.00 | 0.00 | 0.00 | 0.00 |
Oenothera stricta Ledeb. ex Link | America S | H | 0.00 | 0.00 | 0.00 | 0.00 |
Symphyotrichum lanceolatum (Willd.) G.L. Nesom | America N | H | 0.00 | 0.00 | 0.00 | 0.00 |
Eschscholzia californica L. | America N | H / T | 0.00 | 0.00 | 0.00 | 0.00 |
Phytolacca acinosa Roxb. | Eastern Asia | Ch / H | 0.00 | 0.00 | 0.00 | 0.00 |
Ailanthus altissima (Mill.) Swingle | Eastern Asia | P | 0.00 | 0.00 | 0.00 | 0.00 |
Baccharis halimifolia L. | America C | P | 0.00 | 0.00 | 0.00 | 0.00 |
Lonicera japonica Thunb. | Eastern Asia | P | 0.00 | 0.00 | 0.00 | 0.00 |
Mahonia aquifolium (Pursh) Nutt. | America N | P | 0.00 | 0.00 | 0.00 | 0.00 |
Opuntia ficusindica (L.) Mill. | America C | P | 0.00 | 0.00 | 0.00 | 0.00 |
Amaranthus blitoides S. Watson | America N | T | 0.00 | 0.00 | 0.00 | 0.00 |
Datura stramonium L. | America C | T | 0.00 | 0.00 | 0.00 | 0.00 |
Iva xanthifolia Nutt. | America N | T | 0.00 | 0.00 | 0.00 | 0.00 |
Lepidium didymum L. | America S | T | 0.00 | 0.00 | 0.00 | 0.00 |