First database of the impacts of invasive plants in Europe

Freely accessible, the database provides useful contextual information and identifies key gaps in European invasive-plant research.

A team of experts has created the first database of field studies on the impacts of invasive plants on native species, communities and ecosystems in Europe.

The dataset comprises 266 peer-reviewed publications reporting 4,259 field studies on 104 invasive species across 29 European countries. It is the first harmonised database of its kind at continental scale, and is freely accessible to the scientific community for future studies. Notably, one third of the studies focused on just five species that invade several central European countries.

Japanese knotweed (Reynoutria japonica) in a garden in Brastad, Lysekil Municipality, Sweden.

Published in NeoBiota, the project was mainly funded through the European Regional Development Fund (SUMHAL, LIFEWATCH, POPE). It was executed by researchers from the Spanish institutes, Estación Biológica de Doñana, Universidad de Sevilla, Instituto Pirenaico de Ecología and Universidad de Alcalá, as well as the University of Fribourg, Switzerland.

The comprehensive database indicates that invasive plants impact other plants, animals and microbes, all trophic levels (herbivores, parasites, plants, pollinators, predators, omnivores, decomposers and symbionts) and numerous ecosystem processes.

Map of locations (red dots) of field studies on the ecological impacts of invasive plant species in Europe.
Map of locations (red dots) of field studies on the ecological impacts of invasive plant species in Europe. Credit: Vilà et al.

More than half of the studies were conducted in temperate and boreal forests and woodlands and temperate grasslands. Major knowledge gaps are found in Baltic and Balkan countries, in desert and semi-arid shrublands, subtropical forests and high mountains.

Prof. Montserrat Vilà, coordinator of this task, highlights that the database provides information on whether the invasive species increase, decrease or have a neutral effect on the ecological variable of study. This allows investigation into the circumstances in which the invader has contrasting effects.

Himalayan balsam (Impatiens glandulifera). Credit: Guptaele via Wikimedia Commons, CC BY-SA 4.0.

The database will be updated as new field studies on the ecological impacts of invasive species are published. “We hope for more studies on species that are still locally rare and with restricted distribution,” Prof. Montserrat Vilà says, “this database is of interest for academic, management and policy-related purposes.”

The PLANTIMPACTSEUROPE database can be accessed at: https://figshare.com/s/0a890d22bf5632fe5cb5

Research article:

Vilà M, Trillo A, Castro-Díez P, Gallardo B, Bacher S (2024) Field studies of the ecological impacts of invasive plants in Europe. NeoBiota 90: 139-159. https://doi.org/10.3897/neobiota.90.112368

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Did European insects invade the world because settlers carried plants?

Researchers suggest European insect invaders may be so abundant due to colonial introductions of non-native plants.

Insects are among the most prolific and successful invaders of new habitats, but not all regions are equal in the numbers of insects that have spread beyond their borders.


Flows of non-native insects between N. America, Europe, and Australasia. Numbers are the total count of species established from donor to recipient.

European insects, in particular, stand out as highly successful invaders into other world regions. Why? Biologists have long understood that species are spread through international trade: insects are frequent stowaways in trade goods, and the value of international trade between world regions can be a good predictor of how many non-native species are exchanged.

However, recent research led by Dr. Rylee Isitt of the University of New Brunswick, and published in the journal NeoBiota, shows that after accounting for patterns of international trade, the number of insects that have spread from Europe into North America, Australia, and New Zealand far exceeds expectations.

Since patterns in international trade can’t explain these insect invasions, the researchers looked for other potential explanations. It’s possible that European insects are simply more numerous or better invaders than their North American or Australasian counterparts. However, Dr. Isitt and his collaborators didn’t find evidence for that – at most, there are only slightly more European species with the capacity to invade compared to North American and Australasian species.

Another possibility is North American and Australasian habitats are easier to invade than European ones. But prior research has shown that Europe has been heavily invaded by Asian insects, suggesting that it is no more resistant to invasion than North America or Australasia.

Instead, Dr. Isitt and collaborators have proposed that the abundance of European insect invaders may be a result of deliberate introductions of non-native plants into Europe’s colonies. Plants introduced into European colonies could have promoted the spread of European insects into North America and Australia by two different means.

First, insects may have been introduced along with the plants. Second, introduced plants may have provided suitable food and habitat for subsequent arrivals of non-native insects, who might have otherwise found the native flora to be unpalatable or unsuitable as a habitat.

Cumulative discoveries (observed and modelled) and establishments (modelled) of non-native insects exchanged between Europe (EU), North America (NA), and Australasia (AU) versus cumulative import value (inflation-corrected to 2020 British pounds sterling, billions), 1827–2014. Alternating background shading indicates decadal increments, with shading omitted prior to the 1940s for clarity.

Although the researchers haven’t completely resolved the mystery of the overabundance of European insects, they have ruled out several possibilities, leaving the connection to introduced plants as the prime suspect. The next steps? Determining to what extent European insects spread through introduced plants compared to insects from other world regions.

Because invasive species are reshaping our world, we need to understand how they move and establish. Evidence is mounting that trade in plants and plant products is responsible for a large proportion of insect invasions. If the researchers’ hypothesis is correct, the spread of European insects may be a remarkable example of the unintended consequences of deliberate plant introductions.

Research article:

Isitt R, Liebhold AM, Turner RM, Battisti A, Bertelsmeier C, Blake R, Brockerhoff EG, Heard SB, Krokene P, Økland B, Nahrung HF, Rassati D, Roques A, Yamanaka T, Pureswaran DS (2024) Asymmetrical insect invasions between three world regions. NeoBiota 90: 35-51. https://doi.org/10.3897/neobiota.90.110942

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Cost-benefit analysis of strategies against severely harmful giant hogweed in Germany

While invasive species are considered to be a primary driver of biodiversity loss across the globe, species such as the alien for Germany giant hogweed pose even greater risks, including health hazards to humans, limited accessibility to sites, trails and amenity areas, as well as ecological damages.

Since 1st January 2015, EU member states are obligated to develop concrete action plans against (further) spread of invasive alien species. In order to do so, however, policymakers need adequate knowledge about data of the current spread situation as well as information about costs and benefits of control measures. Therefore, German researchers analyse the present situation and control measures, as well as the cost-effectiveness of the possible eradication strategies. Their analysis is published in the open access journal NeoBiota.

Largely spread across Germany, the giant hogweed (H. mantegazzianum) grows in a wide range of habitats, including roadsides, grasslands, riparian habitats and woodland margins. The highest invasion percentage (18.5%) was found for abandoned grasslands, field and grassland margins, and tall-forb stands.

While the species poses a serious threat on native biodiversity through competitive displacement of native plants, it is particularly dangerous to human health. Its watery sap contains several chemical agents. In contact with the skin, this sap can cause severe blistering if the person is simultaneously exposed to sunlight. Furthermore, the hypersensitivity of the skin towards sunlight may persist for a number of years. Additionally, the giant hogweed can limit public accessibility to sites, trails and amenity areas, as well as inflict ecological damages, such as erosion at riverbanks.

In order to provide policymakers with the information needed for adequate control measures, Dr. Sandra Rajmis from the Julius Kühn-Institute, Dr. Jan Thiele from the University of Münster, and Prof. Dr. Rainer Marggraf from Georg-August-Universität Göttingen examine costs and benefits of controlling giant hogweed in Germany.

To address these challenges, the scientists firstly study the present state and costs of control measures, based on survey data received from German nature authorities. Then, they analyse the identified control options in terms of cost effectiveness with regard to the invaded area types and sizes in the infested German districts. To estimate the benefits of the eradication strategies, they turn to a choice experiment survey conducted in German households.

“Only in light of these findings, policymakers can properly understand about the societal costs and benefits of alternatives and decide about societal favored control options in Germany,” point out the researchers.

The team also notes that cost-effectiveness of eradication strategies depends on the length of the period over which they are implemented and observed.

“As this is the first cost-benefit analysis estimating welfare effects and societal importance of giant hogweed invasion control, it could serve as guideline for assessments of eradication control in other European countries and support the implementation of the EU directive 1143/2014,” they conclude.

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Original source: Rajmis S, Thiele J, Marggraf R (2016) A cost-benefit analysis of controlling giant hogweed (Heracleum mantegazzianum) in Germany using a choice experiment approach.NeoBiota 31: 19-41. doi: 10.3897/neobiota.31.8103