The threat of invasive alien species

green nature background for earth day with plant seed in the forest growing on the planet and water around it

The practice of moving plants from one area and releasing them in another, known as plant hunting, can be a contentious issue. It’s a practice that can be seen as disruptive, as it involves removing plants from their natural habitat or introducing non-native species into an ecosystem, which can be highly detrimental. As horticulturists, we hold the power to make more informed choices about the plants we grow, trade, or plant for our gardens, thereby playing a crucial role in biodiversity conservation.

Plants naturally propagate themselves through the most diverse strategies, the range of their environment and the opportunities for life, spreading their seeds through different means: the wind, the sea on which coconuts sail from island to island, birds, animals, and unconsciously, or consciously, via people.

Consider this: every country has its unique flowers and plants, a testament to our planet’s rich biodiversity. However, humanity’s pursuit of globalisation has also left its mark on botanical species, leading to a global flora that is not as diverse as we would hope. This problem is a collective issue that society needs to address.

To put it more urgently, if we don’t act now, we risk losing the unique nature of some places from a botanical perspective.

Needless to say, the fault lies in the transfer and transport of species caused more or less by us humans. Many, many ages ago, we called these people nomadic gatherers; later, they developed into skilled horticulturists and, as in this focus, dedicated plant hunters.

As horticulturists, we are constantly challenged to expand our plant range to meet customer demand. However, it’s crucial that we make informed decisions about the varieties we introduce, considering their impact on the local flora. Our responsibility underscores the importance of our role in biodiversity conservation.

Sometimes, the logistics of importing original plant species into Europe unintentionally introduce contaminants through artificial routes. These unintended consequences, whether from naturally intended releases into the environment or contamination of alien seeds or plants from neighbouring areas, highlight the need for more careful and informed actions.

In a recent video interview on this subject, Dr Lucilla Carnevali of the Department for the Conservation of Biodiversity of ISPRA (Istituto Superiore per la Protezione e la Ricerca Ambientale) discussed the perks and challenges of an international trade that has become faster and busier and tried to answer the question of whether invasive species in ornamental horticulture threatens biodiversity.

Dr Lucilla Carnevali is a professor working for the Department for the Conservation of Biodiversity of ISPRA (Istituto Superiore per la Protezione e la Ricerca Ambientale).

Understanding the numbers

First, it is important to understand the numbers. In assessing the number of plants in Italy and the number of invasive plants, Dr Carnevali referenced the Flora of Italy portal (https://dryades.units.it/floritaly).

This website, launched by the Milan City Council Culture Department in association with the Italian Botanical Society, the Italian Flora Foundation, and ISPRA, is dedicated to showcasing the immense diversity of Italian nature.

The portal’s updated inventory of Italy’s wild plants shows that there are 8,241 native species and 1,782 non-native or alien species, making a total of 10,023 species and subspecies, of which 1,702 are endemic, that is, exclusive to the Italian territory.

The 2024 update records 46 more native species and an increase of at least 185 invasive species compared to 2018.

Extinct species have risen from 26 to 28. These figures confirm that Italy ranks first in Europe and second in the Mediterranean (after Turkey) in terms of the diversity of its floristic patrimony.

Biodiversity hotspots come with great responsibility

Italy is truly a biodiversity hotspot, bringing its people a great moral responsibility for its conservation. That is also reaffirmed in the Italian Constitution: the new versions of Articles 9 and 41 of the Constitutional Charter, amended in 2022, protect the environment, biodiversity, and ecosystems on a par with security, freedom, and human dignity.

The figures also show, however, that Italy ranks second/third in Europe in terms of the rate of invasion by alien plants. These plants are the greatest threat to biodiversity right after habitat destruction, comparable to land consumption.

To combat this phenomenon, already in 2014, the European Union approved a specific Regulation (no. 1143/2014), which is constantly being updated; nevertheless, the number of invasive alien plants present in Italy over the years has increased: 1,023 in 2009, 1,597 in 2018, 1,782 today, of which 20 are included in the European blacklist such as Baccharis halimifolia (saltbush) or Pennisetum setaceum, and as for aquatic plants, Eichhornia crassipes (waterhyacinth) or Ludwigia grandiflora (water primrose).

Few resources are being invested

What is Italy doing about the blacklist? The country is investing very few resources. Although exact up-to-date figures are not available.

The latest report submitted by Italy’s Ministry of the Environment to the EU outlines the expenditures made in 2016-2018 to combat species relevant to the Union: the Italian State invested less than €800,000 in training public officials, informative campaigns, and a study on priorities, while the regions spent €1.8 million on monitoring and control plans.

Some regions set up specific funds but have not yet utilised them, and others, as indicated by the EU, have not implemented any form of management of invasive species. Resources are scarce.

Italy is truly a biodiversity hotspot, bringing its people a great moral responsibility for its conservation.

Italy lacks farsightedness

In 2022, the Ministry of the Environment decided to transfer €5 million per year until 2024 to a dedicated fund for the control of invasive exotic species. The funds are intended exclusively for concrete measures, that is, eradication or control, and not for studies or monitoring.

Dr Carnevali explains, “We need to change pace. Italy lacks the farsightedness to invest before the problem is out of control. The strategic approach to tackling the problem of invasive species is based primarily on prevention.”

She continues, “To counter the introduction into the wild of plant species sold for ornamental purposes; we need to plan the right combination of actions such as promoting good practices -through codes of conduct – among producers and educating the public so as to steer consumers towards native or less invasive species.”

To achieve such goals, unconditional collaboration with green professionals and members of the public is required. This will eventually lead to more informed buying and selling decisions and raise awareness.

The recipients are, first and foremost, the industry stakeholders, including cut flower and houseplant nurseries, importers, floral wholesalers, tree nurseries, retailers, garden centres, major e-commerce platforms, and the organisers of biodiversity events.

It is also necessary to involve public administrations, which have an active role in selecting, managing and maintaining ornamental plant species in public or private environments.

Non-native exotics can be harmful

Invasive species of EU relevance are non-native, exotic species introduced into an ecosystem that harm the environment, its biodiversity, economy, or human health. Their impact is such that they require concerted action at the EU level.

Carnevali calls for raising awareness and minimising the contamination of goods, vehicles, and equipment by invasive alien species. She notes, “Little is still known about the impact of invasive alien plant species spread into the natural environment outside the scientific field, with the exception of some of the species that have become well-known to the public.”

Due to a lack of information, some invasive alien species are purchased and used without full awareness of the environmental damage they could cause by spreading into natural environments, as in the case of Carpobrotus edulis planted in sand dunes.

Carpobrotus edulis, aka hottentot-fig, is a ground-creeping succulent plant native to South Africa. It forms wide mats with fleshy leaves that are long and triangular, initially yellow to grass green, later turning redder in colour. The plant can significantly impact coastal sand dunes. As an invasive species, it changes the natural ecosystem by outcompeting native plants, destabilising dune structures, and reducing biodiversity.

Its dense mats prevent other plants from establishing, leading to soil erosion and changes in sand movement patterns. Conservation efforts often focus on managing its spread to protect dune ecosystems.

A minimum of common sense and education would suffice to suggest carefully and correctly using the variety, such as growing Carpobrotus edulis in pots. This action would prevent the invasive spread of the variety.

Carnevali advocates the dissemination of the already available information material on the subject as widely as possible, both to the general public and to retailers. She says, “In particular, the brochure ‘From Balconies to City Parks: Good Practices for Conscious Gardening’, produced in association with Società Botanica Italiana and ANVE, Italy’s National Association of Nursery Stock Exporters. The brochure’s text aims to raise awareness in the professional sector and the general public about the responsible use of ornamental plants while also providing valuable suggestions for using alternative (native) species that have similar ornamental characteristics.”

The ultimate goal, however, is creating a proper technical manual. Such a compendium should serve to identify ornamental plants, ideally native or, at the very least, exotic but non-invasive. She adds, “Plants that can be used as an alternative to the invasive exotic plants still available at local nurseries, thus helping to avoid their introduction into the natural environment.”
Carnevali’s analysis is insightful and provides food for thought for a new, more collaborative style between industry bodies and members of the public.

The ideas behind Conscious Greenery must reach the nurseries. By involving local residents, sector professionals, and ministerial technicians in the problems that need to be resolved, there will be renewed and passionate civic involvement, together with solutions that are understood by all.

This article was first published in the June 2024 issue of FloraCulture International.