Tag: invasive plants

Listen to the trees: a detective work on the origin of invasive species

An attempt to explore the history of the spread of four non-indigenous invasive tree species in one of the most important Hungarian forest-steppe forests of high conservation value.

Guest blog post by Arnold Erdélyi, Judit Hartdégen, Ákos Malatinszky, and Csaba Vadász

Today, almost everyone is familiar with the term “biological invasion”. Countless studies have been carried out to describe the various processes, and explore the cause and effect, and several methods have been developed in order to control certain invasive species. However, one of the biggest puzzles is always the question of how it all happened. It is not always easy to answer, and, in general, the smaller the area, the more difficult or even impossible it is to answer. In the course of our work, we attempted to explore the history of the spread of four, non-indigenous invasive tree species in one of the most important Hungarian forest-steppe forests of high conservation value, the Peszér Forest (approximately 1000 ha). Last week, we published our study in the journal One Ecosystem.

An open formation of the Eurosiberian steppic woods with Quercus spp., a priority natural habitat type of Community interest under the European Union’s Habitats Directive
A closed formation of steppic oak forest with a dense shrub layer and a herb layer dominated by the lily of the valley (Convallaria majalis).

The Far Eastern tree of heaven (Ailanthus altissima), as well as the North American black cherry (Prunus serotina), the box elder (Acer negundo) and the common hackberry (Celtis occidentalis) are among the worst invasive plant species in Hungary. They are also responsible for serious conservation and economic problems in the Peszér Forest.

Invasion of tree of heaven (top left) and common hackberry (top right) in poplar stands, carpet of seedlings of black cherry (bottom left), and monodominant stand of box elder, regrown from stump after cutting (bottom right)

Historical reconstructions of the spread of invasive species are most often based on only one, or sometimes a few aspects. We used six approaches simultaneously:

  • we reviewed the published and grey literature,
  • extracted tree species data from the National Forest Database since 1958,
  • conducted a field survey with full spatial coverage (16,000 survey units (25×25 m quadrats)) – instead of sampling,
  • recorded all the largest (and presumably the oldest) individuals for annual ring counts,
  • performed hotspot analyses on the field data
  • collected local knowledge.
Cutting down the oldest common hackberry trees in order to count the annual rings from trunk discs

Our results show that each approach provided some new information, and without any of them the story revealed would have been much shorter and more uncertain. We have also highlighted that at the local level, the use of one or two aspects can be not only inadequate but also misleading.

From the literature it was possible to determine the exact place and date of the first occurrence of the tree of heaven and the black cherry. However, in the case of black cherry, for example, it was only possible to piece together the circumstances of the first plantings by combining three different sources. The first occurrences of box elder were found in forestry data. Finally, in the case of the common hackberry, searching for old individuals and determining their age gave the best results.

Common hackberry in the Peszér forest according to the recent forestry data (2016) and the field survey (2017-2019). The difference is clear: in the official forestry database, the tree species is underrepresented several times over

A well-explored story of a biological invasion can go a long way in making more and more people understand that controlling these non-indigenous species can only be beneficial. On the other hand, it can also help to strengthen conservation efforts, for example by increasing the volunteer workforce, which can be a major factor in the reduction of certain species. We hope that our work and the approaches we have taken will serve as a good model for exploring other invasion stories around the world.

Winter snapshot from the Peszér Forest, a diverse forest edge habitat along an inner road.

Research article:

Erdélyi A, Hartdégen J, Malatinszky Á, Vadász C (2023) Historical reconstruction of the invasions of four non-native tree species at local scale: a detective work on Ailanthus altissima, Celtis occidentalis, Prunus serotina and Acer negundo. One Ecosystem 8: e108683. https://doi.org/10.3897/oneeco.8.e108683

Can we predict if a plant species will become exotic?

A new approach compared characteristics of species that succeeded or failed to establish after probably following the same historical introduction route.

Plant species become exotic after being accidentally or deliberately transported by humans to a new region outside their native range, where they establish self-perpetuating populations that quickly reproduce and spread. This is a complex process mediated by many factors, such as plant traits and genetics, which challenges the creation of general guidelines to predict or manage plant invasions. Scientists from Spanish and Australian institutions have now defined a new framework to find the predictors of invasiveness, investigating species that have succeeded or failed to establish abroad after following similar historical introduction routes.

Dr Javier Galán Díaz, University of Seville, Spain, Dr Enrique G. de la Riva, University of León, Spain, Dr Irene Martín-Forés, The University of Adelaide, Australia, and Dr Montserrat Vilà, Doñana Biological Station (EBD-CSIC), Spain, described their findings in a new paper in the open-access journal NeoBiota.

Ancient agricultural landscape dominated by plant species introduced in other Mediterranean regions (Parque Natural de Los Alcornocales, Andalucía, Spain). Photo by Dr Javier Galán Díaz

“While current policies exert strong control on the import and export of living organisms, including pests, across countries, until only a few decades ago, very little attention was paid to this issue. This means that many species were translocated to new regions without any consideration of their potential impacts,” says Dr Javier Galán Díaz.

An example of this is the massive plant exchange among Mediterranean‐type regions as a consequence of European colonialism: crops and cattle were exported, along with tools and materials, potentially bringing along the seeds of many plant species.

Agricultural landscape dominated by exotic species of European origin (Merced Vernal Pool and Grassland Reserve, California, U.S.A.). Photo by Dr Javier Galán Díaz

“So far, most studies on plant invasions have tried to explain the success of exotic species by comparing their traits with those of the native plant communities where they arrive, or by comparing the traits of plant species that have achieved different levels of invasion in the same region. But, if we take into account that the most common plant species from European agricultural landscapes have been in contact with humans and have therefore had the potential to be inadvertently transported to other Mediterranean regions, then only those that have successfully invaded other regions have something different in them that allowed them to establish and spread abroad,” Dr Galán Díaz explains.

Following this approach, the scientists found that, when comparing plant species transported from the Mediterranean Basin to other Mediterranean-climate regions (California, Central Chile, the Cape Region of South Africa and Southwestern and South Australia) in the search of predictors of invasiveness, only those species with large distribution ranges that occupy climatically diverse habitats in their native region became exotic. Also, species with many dispersal vectors (for instance those that have seeds dispersed by animals, water or wind), long bloom periods and acquisitive above- and belowground strategies of resource use are most likely to become exotic. Most of this plant information is readily available or easy to obtain from free and open-access repositories.

  • Lotus corniculatus, one of the species that the study identified as invasive in other Mediterranean-climate regions of the world. Photo by Teresa Grau Ros under a CC-BY 2 license
  • Rumex acetosella, one of the species that the study identified as invasive in other Mediterranean-climate regions of the world. Photo by Jakub T. Jankiewicz under a CC-BY 2 license
  • Carduus tenuiflorus, one of the species that the study identified as invasive in other Mediterranean-climate regions of the world. Photo by jacinta lluch valero under a CC-BY 2 license
  • Poa pratensis, one of the species that the study identified as invasive in other Mediterranean-climate regions of the world. Photo by AnneTanne under a CC BY-NC-SA 2 license

“Determining the factors that pre-adapt plant species to successfully establish and spread outside of their native ranges constitutes a powerful approach with great potential for management,” the researchers write in their paper. “This framework has the potential to improve prediction models and management practices to prevent the harmful impacts from species in invaded communities.”

“Using the existing information, we can identify the key species to monitor. This is especially encouraging in the era of Big Data, where observations from citizen science applications add to those of scientists, increasing the potential of screening systems,” Dr Galán Díaz says in conclusion.

Research article:

Galán Díaz J, de la Riva EG, Martín-Forés I, Vilà M (2023) Which features at home make a plant prone to become invasive? NeoBiota 86: 1-20. https://doi.org/10.3897/neobiota.86.104039

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Study ranks potentially harmful invasive species in Ghana

Scientists ranked the 110 arthropod and 64 pathogenic species posing the greatest potential threat to the country if established.

A CABI-led study has conducted a comprehensive survey of nearly 200 potentially harmful alien plant species that could have a detrimental impact upon agriculture, forestry and biodiversity in Ghana once they enter the country.

Invasive Alien Species (IAS) continue to shape the global landscape through their effects on biological diversity and agricultural productivity. The effects are particularly pronounced in Sub-Saharan Africa, which has seen the arrival of many IAS in recent years. This has been attributed to porous borders, weak cross border biosecurity, and inadequate capacity to limit or stop invasions.

A farmer shows cassava root affected by cassava brown streak virus alongside a healthy root in a country where the disease is present – one of the 64 pathogens assessed by the scientists. Credit: CABI

The research, the findings of which are published in the journal NeoBiota, ranks 110 arthropod and 64 pathogenic species that pose the greatest threat but are not yet officially present in the country. However, they could arrive as ‘stowaways’ in cargo from other countries around the world, the scientists believe.

Dr Marc Kenis, Head Risk Analysis and Invasion Ecology at CABI, led on the horizon scanning exercise supported by colleagues from a range of institutions including Ghana’s Plant Protection and Regulatory Services Directorate (PPRSD).

Among the top arthropods prioritised by Dr Kenis and his team were the pink hibiscus mealybug (Maconellicoccus hirsutus Green) and melon thrips (Thrips palmi Karny) while the top pathogens highlighted include cassava brown streak virus and Maize lethal necrosis disease.

Cassava in Ghana, for example, is a main staple crop and contributes about 22% and 30% to the Agricultural Gross Domestic Product (AGDP) and daily calories intake respectively. The crop, however, can be at risk from cassava brown streak virus which can reduce yields by up to 70%.

Maize lethal necrosis disease, on the other hand for instance, can be a major disruptor of maize crops in Ghana where maize accounts for more than 50% of the country’s total cereal production. The disease can cause losses of between 50-90% depending on the variety of maize and the growing conditions of the year.

The scientists also found other species recorded in Africa that included 19 arthropod and 46 pathogenic species which were already recorded in the neighbouring countries of Burkina Faso, Côte d’Ivoire, and Togo.

Dr Kenis, who is based at CABI’s centre in Switzerland, said, “The ultimate objective of this research was to enable prioritization of actions including pest risk analysis, prevention, surveillance and contingency plans. Prioritisation was carried out using an adapted version of horizon scanning and consensus methods developed for ranking IAS worldwide.

“We have demonstrated that through horizon scanning, a country can identify potential invasive plant pests, both invertebrates and pathogens, and use the information to determine the risk associated with each.

“This will enable the country to invest the limited resources in priority actions such as preventing arrival and establishment of IAS, Pest Risk Analysis (PRA), surveillance and developing contingency plans.

“This study can serve as a model for future projects on plant pests’ prioritisation in Africa and elsewhere. It would be applicable for assessing the risk of invasive plant pests in any country or region, e.g. trade blocks, with minor modifications of the method, particularly in the mini-PRA protocol used to score species.”

The full lists of arthropod and pathogenic species surveyed can be found within the full paper which can be read online.

Mr Prudence Attipoe, Deputy Director Head Plant Quarantine Division, PPRSD, said, “The horizon scanning exercise for Ghana would give the PPRSD an insight into invasive pests which could possibly enter the Nation. The tool is timely and appropriate for conducting PRA for planning, training and future preparedness. The success of this exercise would pre-empt the introduction of these invasive pests into the country in order to protect Ghana’s agriculture, forestry and also cause staff of PPRSD to be more vigilant at the borders for these pests.”

Research paper:

Kenis M, Agboyi LK, Adu-Acheampong R, Ansong M, Arthur S, Attipoe PT, Baba A-SM, Beseh P, Clottey VA, Combey R, Dzomeku I, Eddy-Doh MA, Fening KO, Frimpong-Anin K, Hevi W, Lekete-Lawson E, Nboyine JA, Ohene-Mensah G, Oppong-Mensah B, Nuamah HSA, van der Puije G, Mulema J (2022) Horizon scanning for prioritising invasive alien species with potential to threaten agriculture and biodiversity in Ghana. NeoBiota 71: 129 148. https://doi.org/10.3897/neobiota.71.72577

An invasive plant may cost a Caribbean island 576,704 dollars per year

Guest blog post by Wendy Jesse

Coralita overgrowing vegetation. Photo from https://www.wur.nl/en/show/invasive-plants-in-caribbean-netherlands.htm

A recent study in One Ecosystem has estimated the severe loss of ecosystem service value as a result of the widespread invasion by the plant species Coralita (Antigonon leptopus) on the Caribbean island of St. Eustatius. The results illustrate the drastic impact that a single invader can have on the economy of a small island and inform policy makers about priority areas for invasive species management.

See for full article: Huisman, S., Jesse, W., Ellers, J., & van Beukering, P. (2021). Mapping the economic loss of ecosystem services caused by the invasive plant species Antigonon leptopus on the Dutch Caribbean Island of St. Eustatius. One Ecosystem, 6, e72881. https://doi.org/10.3897/oneeco.6.e72881

The invader: Coralita

  • Flowering coralita, creeping vertically over fences and horizontally across the ground.
  • Coralita intertwined with electricity box and cables. Photo by Adam Mitchell

Coralita is a fast-growing, climbing vine with beautiful pink or white flowers. Originally from Mexico, it was introduced as a popular garden plant to many Caribbean islands and around the world. Its fast-growing nature means that it can outcompete most native species for terrain, quickly becoming the dominant species and reducing overall diversity (Jesse et al. 2020, Nature Today 2020, Eppinga et al. 2021a). This is especially the case on St. Eustatius, where published ground surveys indicate that the plant already appears on 33 percent of the island.

Losses of ecosystem services

Coralita overgrowing cars. Photo by Rotem Zilber

We estimated the total terrestrial ecosystem service (ES) value on St. Eustatius to be $2.7 million per year by mapping five important terrestrial ecosystem services: Tourism, Carbon sequestration, Non-use (i.e., intrinsic biodiversity) value, Local recreational value, and Archeological value. Subsequently, we calculated Coralita-induced loss of ecosystem services under two realistic distributional scenarios of Coralita cover on the island: 3% of island dominantly covered (based on Haber et al. 2021, Nature Today 2021) and 36% dominant cover (if entire range would reach dominant coverage), causing an annual ES value loss of $39,804 and $576,704 respectively. The highest ES value (17,584 $/ha/year) as well as the most severe losses (3% scenario: 184 $/ha/year; 36% scenario: 1,257 $/ha/year) were located on the dormant Quill volcano; a highly biodiverse location with popular hiking trails for locals and tourists alike.

Consequences for policy makers and practitioners

Coralita blocking water a drainage channel. Photo by Wendy Jesse.

There is an urgent need for studies such as this one that help to bridge the gap between academia and policy planning, as these translate abstract numbers into intuitive information. Instead of invasive species being just a biological term, direct impacts on people’s value systems and sources of income immediately strike a chord. I experience this on a daily basis, because in addition to being a coauthor on this paper, I currently work as a policy employee in nature protection and management.

Coralita overgrowing archeological heritage on St. Eustatius. Photo from St. Eustatius Center for Archeological Research (SECAR)

This study helps to prioritize locations for invasive species prevention, management, eradication, and restoration. It is imperative that invasive species do not reach locations of high ecosystem service value. Management of isolated satellite patches of Coralita close to locations of high ES value will likely be most effective in halting the plant’s invasive spread (Eppinga et al. 2021b). Setting up a targeted monitoring and rapid response strategy, as well as legislation for biosecurity measures to prevent other invasive species from entering the island, would likely help to reduce impacts on the important ecosystem services on St. Eustatius.

References

Academic literature:

Eppinga, M. B., Haber, E. A., Sweeney, L., Santos, M. J., Rietkerk, M., & Wassen, M. J. (2021a). Antigonon leptopus invasion is associated with plant community disassembly in a Caribbean island ecosystem. Biological Invasions, 1-19.

Eppinga M, Baudena M, Haber E, Rietkerk M, Wassen M, Santos M (2021b) Spatially explicit removal strategies increase the efficiency of invasive plant species control.

Ecological Applications 31 (3): 1‑13. https://doi.org/10.1002/eap.2257Haber E, Santos M, Leitão P, Schwieder M, Ketner P, Ernst J, Rietkerk M, Wassen M, Eppinga M (2021) High spatial resolution mapping identifies habitat characteristics of the invasive vine Antigonon leptopuson St. Eustatius (Lesser Antilles). Biotropica 53 (3): 941‑953. https://doi.org/10.1111/btp.12939

Jesse, W. A., Molleman, J., Franken, O., Lammers, M., Berg, M. P., Behm, J. E., … & Ellers, J. (2020). Disentangling the effects of plant species invasion and urban development on arthropod community composition. Global change biology, 26(6), 3294-3306.

Blog posts on Nature Today website:

van Maanen, G. Molleman, J., Jesse, W.A.M. (2020) Drastic effects of coralita on the biodiversity of insects and spiders. Nature Today. naturetoday.com/intl/en/nature-reports/message/?msg=26339

Dutch Caribbean Nature Alliance (2021) Using satellite imagery to map St. Eustatius’ coralita invasion. Nature Today. naturetoday.com/intl/en/nature-reports/message/?msg=28317

NeoBiota invites risk analysis studies in a new Special Issue on advancements in the screening of freshwater and terrestrial non-native species

The “Recent advancements in the risk screening of freshwater and terrestrial non-native species” Special Issue in the open-access, peer-reviewed scholarly journal NeoBiota is now open for submissions. The deadline for submission is 30 April 2022, with the issue scheduled for publication in August 2022.

The “Recent advancements in the risk screening of freshwater and terrestrial non-native species” Special Issue in the open-access, peer-reviewed scholarly journal NeoBiota is now open for submissions.

The issue is managed by the international team of guest editors of Dr Daniela Giannetto (Mugla Sitki Kocman University, Turkey), Prof. Marina Piria (University of Zagreb, Croatia), Prof. Ali Serhan Tarkan (Mugla Sitki Kocman University, Turkey) and Dr Grzegorz Zięba (University of Lodz, Poland).

Update: The deadline for submission has been extended to 30 April 2022, with the issue expected to be published in August 2022. 

The new special issue is expected to collate prominent contributors from the field of invasive ecology, thereby addressing existing gaps in the knowledge about both freshwater and terrestrial non-native species and their management.

The editors note that despite the current efforts and measures to monitor and tackle the spread of non-native species, and especially those posing imminent threat to local biodiversity and ecosystems, further expansion of such populations has increasingly been recorded in recent years. Of special concern are developing countries, where legislation for controlling non-native species is still lacking.

A major problem is that – as of today – we are still missing on risk screening studies needed to provide evidence for the invasiveness potential of many non-native species across several taxonomic groups, which would then be used to support specific conservation efforts. Unfortunately, this is particularly true for species inhabiting the world’s biodiversity hotspots, point out the editors.

Risk-based identification of non-native species is an essential process to inform policy and actions for conservation and management of biodiversity. Previously published papers on risk screening of aquatic non-native species, and especially those using the most widely-employed ‘-ISK’ decision-support toolkits, have attracted mounting interest from the wider scientific community.

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Roadside invader: the higher the traffic, the easier the invasive common ragweed disperses

Common ragweed is an annual plant native to parts of the United States and southern Canada. It’s an invasive species that has spread to Europe. An important agricultural weed, this plant is particularly well-adapted to living at roadsides, and there are several theories why.

Its rapid expansion in Europe can’t be explained by its natural dispersal rate, which is limited to distances of around 1 meter. Rather, there are other factors in play, human-mediated, that support its invasion success – along roads, for example, it spreads mainly thanks to agricultural machineries, soil movements, roadside maintenance and road traffic.

Common ragweed. Photo: Uwe Starfinger

Studying common ragweed’s distribution patterns is important, because its allergenic pollen affects human health, mainly in southeast Central Europe, Italy and France. Finding out where it thrives, and why, can help with the management and control of its populations.

This is why scientists Andreas Lemke, Sascha Buchholz, Ingo Kowarik and Moritz von der Lippe of the Technical University of Berlin and Uwe Starfinger of the Julius Kühn Institute set out to explore the drivers of roadside invasions by common ragweed. Mapping 300 km of roadsides in a known ragweed hotspot in Germany’s state of Brandenburg, they recorded plant densities at roadsides along different types of road corridors and subject to different intensities of traffic over a period of five years. They then explored the effect of traffic density and habitat type, and their interactions, on the dynamics of these populations. Their research is published in the open-access, peer-reviewed journal NeoBiota.

Surprisingly, high-traffic road cells displayed a consistently high population growth rate even in shaded and less disturbed road sections – meaning that shading alone would not be enough to control ragweed invasions in these sections.  Population growth proceeded even on roadsides with less suitable habitat conditions – but only along high-traffic roads, and declined with reduced traffic intensity. This indicates that seed dispersal by vehicles and by road maintenance can compensate, at least partly, for less favorable habitat conditions. Disturbed low-traffic road cells showed constantly high population growth, highlighting the importance of disturbance events in road corridors as a driver for common ragweed invasions.

These findings have practical implications for habitat and population management of ragweed invasions along road networks. Reducing the established roadside populations and their seed bank in critical parts of the road network, introducing an adjusted mowing regime and establishing a dense vegetation layer can locally weaken, suppress or eradicate roadside ragweed populations.

Original source:Lemke A, Buchholz S, Kowarik I, Starfinger U, von der Lippe M (2021) Interaction of traffic intensity and habitat features shape invasion dynamics of an invasive alien species (Ambrosia artemisiifolia) in a regional road network. NeoBiota 64: 55-175. https://doi.org/10.3897/neobiota.64.58775

Experiment suggests the best ways to tackle invasive Oregon grape in Belgian coastal dunes

The Belgian coastal dunes, a protected habitat of high conservation value, are getting severely impacted by one of its worst enemies amongst invasive species: the Oregon grape. To help mitigate the detrimental effect of this North American shrub invader, Belgian scientists carried out an experiment to assess the effectiveness of different management methods.

The Belgian coastal dunes, a protected habitat of high conservation value, are getting severely impacted by one of its worst enemies amongst invasive species: the Oregon grape. To help mitigate the detrimental effect of this North American shrub invader, Belgian scientists carried out an experiment to assess the effectiveness of different management methods.

The Atlantic coastal dunes form a dynamic and diverse ecosystem, home to a large number of native species, many of which are regionally threatened. Embryonic dunes, shifting white dunes, moss dunes, dune grasslands, and dune slacks are considered high conservation value sites, according to the interpretation manual of European habitats. However, the dunes are highly affected by external influences, and one of the most important threats to their biodiversity are invasive non-native plant species. These plants often colonised the dunes as garden escapes or spread from garden waste dumps or public plantings. Oregon grape is one of the worst invaders amongst them.

Oregon grape growing on sand dune (Belgium).
Photo by Tim Adriaens.

In their study, published in the open-access journal NeoBiota, the scientists, led by Tim Adriaens and Sam Provoost of the Research Institute for Nature and Forest (INBO), focus on the management of the current populations of Oregon grape (Berberis aquifolium) in the Belgian coastal dunes, where the species has already managed to invade half of the 46 nature reserves and is starting to replace native vegetation. Such a negative effect on the biodiversity of the area requires practical management advice. Due to the high level of infestation of the dunes, the researchers recommend prompt eradication as the most appropriate management strategy. So far, however, it has been unclear which method would show the best effectiveness.

“Invasive shrub species exert an additional pressure on Belgian dune ecosystems, which are already highly fragmented by urbanisation. Oregon grape is one of the worst and should be tackled urgently before it gets out of control,” says Tim Adriaens.

Having compared four previously suggested treatments: manual uprooting, foliar herbicide application, stem cutting followed by herbicide and salt application, the scientists reported herbicide leaf treatment to be the most effective method. Manual removal by digging and treating stems with glyphosate showed medium effectiveness. Treating stems with a saturated salt solution appeared rather cosmetic. However, it’s not that easy to choose which method would be the best to work with, since with herbicide use there are non-target effects on the environment, economy, and society to be considered.

Dune restoration by mechanical removal of dense Oregon grape infestation (left) and leaf treatment of Oregon grape clone with a hand sprayer (right).
Photo by Tim Adriaens.

“Individual clones are best treated with herbicide, large surface areas provide opportunities for landscape-scale ecological restoration, combining invasive shrub removal with sand dune creation,” further explains Tim Adriaens.

In Belgium, Oregon grape was first recorded in the wild in 1906 and naturalised in the period 1920-1950. It has been spreading rapidly since the 1990s. This expansion might be linked to cultivated hybrids and global warming, with the latter leading to a lengthened growing season, suggest the scientists. The species likes calcareous soils. Along the Belgian coast, Oregon grape has mainly invaded grey dunes, scrub and woodland.

Thanks to its numerous blue berries, which are easily dispersed over long distances by songbirds, the plant can appear everywhere within the dunes sites, also in places hardly accessible to managers. With the help of a highly branched root system, the plants attach themselves firmly in the sand, which makes manual pulling of mature plants hardly possible and labor-intensive.

“Dune managers and scientists across Europe should unite to draft alert lists and prioritise established alien species for management,” Tim says in conclusion.

In conclusion, the scientists highlight the importance of an EU-wide collaboration between scientific communities. Invasive species are not bothered by administrative borders and exchanging experiences on impact and management options is crucial to maintain dune ecosystems in good conservation status.

Coastal dunes in Belgium provide unique habitat to many Red listed species.
Photo by Tim Adriaens.

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Original source

Adriaens T, Verschelde P, Cartuyvels E, D’hondt B, Vercruysse E, van Gompel W, Dewulf E, Provoost S (2019) A preliminary field trial to compare control techniques for invasive Berberis aquifolium in Belgian coastal dunes. NeoBiota 53: 41-60. https://doi.org/10.3897/neobiota.53.38183

Invasive alien plant control assessed for the Kruger National Park in South Africa

Along with urban and agricultural encroachment and pollution mitigation, managing invasive alien species is a key intervention needed to protect biodiversity. Unfortunately, on a global scale there are not enough funds to meet the requirements for effective conservation everywhere, which means that scarce funds need to be allocated where they can be used most efficiently.

In order to find out whether the historical measures undertaken at the Kruger National Park in South Africa have been effective and optimised, researchers led by Prof. Brian W. van Wilgen of Stellenbosch University assessed the invasive alien plant control operations in the protected area over several decades. Their findings and recommendations are published in the open access journal Neobiota.

While the first invasive alien plants in the national park, which stretches over two million hectares, were recorded back in 1937, it was not until the mid-1950s that attempts at controlling them began. By the end of the century, the invasive alien plant control program had expanded substantially.

Dense invasions of the West Indian Lantana (Lantana camara) along the Sabie River in the Kruger National Park have required intensive mechanical and chemical control to clear.
Dense invasions of the West Indian Lantana along the Sabie River in the Kruger National Park have required intensive mechanical and chemical control to clear.

However, the scientists found out that despite several invasive alien species having been effectively managed, the overall control effort was characterised by several shortcomings, including inadequate goal-setting and planning, the lack of a sound basis on which to apportion funds, and the absence of any monitoring of control effectiveness.

Furthermore, the researchers report that over one third (40%) of the funding has been spent on species of lower concern. Some of these funds have been allocated so that additional employment could be created onsite, or because of a lack of clear evidence about the impact of certain species.

As a result of their observations, the team concludes three major strategies when navigating invasive alien species control operations.

Firstly, a thorough assessment of the impact of individual species needs to be carried out prior to allocating substantial funds. On the other hand, in case of a new invasion, management needs to be undertaken immediately before any further spread of the population and the subsequent rise in control costs. Monitoring and assessments have to be performed regularly in order to identify any new threats that could potentially be in need of prioritisation over others.

Secondly, the scientists suggest that the criteria used to assign priorities to invasive alien species should be formally documented, so that management can focus on defensible priorities. They propose using a framework employing mechanisms of assessments used in the International Union for Conservation of Nature‘s Global Invasive Species Database.

The authors also point out that re-allocating current funds to species of greater concern is needed for species that cannot be managed via less expensive solutions such as biological control. Taking care of alien plant populations living outside of the park, but in close proximity, is also crucial for the prevention of re-invasions of already cleared areas.

Sunset Dam heavily infested with water lettuce (left). The population was effectively eliminated by a combination of biological and chemical control (right).
Sunset Dam heavily infested with water lettuce (left). The population was effectively eliminated by a combination of
biological and chemical control (right).

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Original source:

van Wilgen BW, Fill JM, Govender N, Foxcroft LC (2017) An assessment of the evolution, costs and effectiveness of alien plant control operations in Kruger National Park, South Africa. NeoBiota 35: 35-59. https://doi.org/10.3897/neobiota.35.12391

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

Black wattle’s new biogeographic distribution threatens flight safety in China

Black wattle, flowering trees also known as the Australian acacia, have been observed to rapidly spread around local airports in Yunnan province, southwestern China. According to the ecologists, this alien species and its extraordinary pace of invasion are to lead to new threats for both flight safety and local biodiversity. The five Chinese scientists, led by Min Liu, PhD student at Yunnan University, have their findings and suggestions for immediate measures published in the open-access journal Neobiota.

The phenomenon was investigated by the ecologists and botanists, affiliated with Yunnan University and Kunming University of Science and Technology, at Kunming’s Changshui International Airport.

The black wattle is listed as being among the ”Top 100 of the world’s worst invasive alien species” by the World Conservation Union (IUCN). Native to Australia, the species has been settled across the globe for more than 150 years owing to its multiple uses. However, its distribution and expansion are generally overlooked in China.

It is an evergreen fast growing flowering tree species, which is strongly dependent on sunlight and contributes to nitrogen fixation. This means that due to bacteria in its root system, the tree produces nitrogen compounds that help the plant grow and compete with other plants. Once dead, it would release these compounds to fertilise the soil.

During their investigation, the scientists observed a total seedling spread of 1800 m in 2013, with its peak growth taking place between June and November. Other population features such as number, density, height and ground diameter, also showed that the species had a very high invasion rate.

The authors conclude that black wattle has a strong potential to change the local vegetation structure and increase the risk of bird strikes. It is of urgent need that the situation is further assessed and the potential invasion threat at other airports around China and other parts of the world – evaluated.

“I have never found such a rapid expansion like the one of the black wattle trees at this airport in my career,” said the Head of Bird Strike Prevention Office of Changshui Airport. “These trees grow very fast and provide good shelters for local birds, which eventually increases the probability of bird strikes at our airport. So, they must be controlled.”

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Original source:

Liu M, Yang M, Song D, Zhang Z, Ou X (2016) Invasive Acacia mearnsii De Wilde in Kunming, Yunnan Province, China: a new biogeographic distribution that Threatens Airport Safety.NeoBiota 29: 53-62. doi: 10.3897/neobiota.29.7230