Gardeners on the front line: the key to early invasive plant detection?

A study from the United Kingdom suggests gardeners could partner with researchers to play a crucial role in preventing plant invasions.

The critical role of gardeners in identifying ‘future invaders’ – ornamental plants that could become invasive species – has been revealed by researchers from the University of Reading and the Royal Horticultural Society.

Looking to draw from the experience of Britain’s millions of gardeners, the team created an online survey where gardeners reported ornamentals that showed ‘invasive behaviour’ in their gardens.

Based on reports from 558 gardeners, 251 different plants were identified as potential invaders, reflecting the extensive variety and potential risks in domestic gardens. The team analysed the results, considering both domestic and global invasive status, and prioritised ornamental plants of concern. The result was a shortlist of plants which need their invasive potential in Britain and Ireland assessed.

The shortlisted plants include, for example: Mexican fleabane (Erigeron karvinskianus); cypress spurge (Euphorbia cyparissias); chameleon plant (Houttuynia cordata); Himalayan honeysuckle (Leycesteria formosa); and purple top (Verbena bonariensis).

The results, published in the open-access journal NeoBiota, highlight the role of gardeners in the early detection of invasive species, a key factor in the global nature crisis. Such proactive identification could prove invaluable for future risk assessments and prevention strategies.

“The simple yet structured scheme we developed was used to prioritise which of the around 70,000 ornamental plants available to buy in the UK could be future invaders. This is crucial for focusing research efforts and resources, such as conducting formal risk assessments to explore the invasive potential of those shortlisted.”

Tomos Jones, lead author

John David, RHS Head of Horticultural Taxonomy, said: “It’s important to remember that these shortlisted plants are not yet officially invasive, and that many non-native plants that occur in the wild present no threat to our native biodiversity.”

The research team encourages gardeners to get involved in helping identify future invaders. They can report ornamental plants showing ‘invasive behaviour’ through an ongoing project called Plant Alert, run by the Botanical Society of Britain and Ireland and Coventry University.

Original source:

Jones TS, Culham A, Pickles BJ, David J (2024) Can gardeners identify ‘future invaders’? NeoBiota 91: 125–144. https://doi.org/10.3897/neobiota.91.110560

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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