Work in progress: CONTROL OF INVASIVE SPECIES

Invasive alien species are found outside their native range as a result of accidental or deliberate introduction by humans. These species often die, but in some cases they may thrive in their new environment and proliferate.

They disrupt the ecological balance, competing directly with native species – either through predation or by reducing the available food niches – or indirectly, for example by introducing new pests.

The Trentino region has also been affected by the appearance of these species for several years. Within the NatConnect2030 project, an entire work package is dedicated to this issue, with the following operational tasks:

• T.5.3 ‘Measures to remove widespread but controllable animal species’
• T.5.4 ‘Measures to remove widespread but controllable plant species’.
• Some actions are also being carried out as part of task 2.3 “Measures to improve the conservation status of the freshwater crayfish (A. pallipes) populations and their habitat”.

American turtles

Work has been underway for several years now to contain the American pond turtle (Trachemys scripta), a species that has been on the list of invasive species of Union-wide significance for some time.
These turtles, which were once widely sold, have a negative impact on the aquatic communities in the environments where they live, in particular by preying on fish fry, tadpoles and insect larvae, as well as the eggs and chicks of waterbirds. This animal can also act as a vector for the transmission of bacteria of the genus Salmonella.

In Trentino, the species is now widespread in almost all the main lakes and small water bodies across the region, due to owners abandoning them. The aim of these measures is therefore to contain the population in those water bodies situated within protected areas, where the microfauna communities are more diverse, by capturing the fish using traps. Two types of trap are used: an atoll trap and a semi-floating cage, both of which are checked regularly to prevent unnecessary suffering to the animals. The captured animals are sent to suitable centres, which have ponds and water basins not connected to the river network, allowing them to live in appropriate conditions without the risk of them having a negative impact on the local fauna.

American crayfish

The native crayfish, Austropotamobius pallipes, also faces the threat of invasive species. It is, in fact, under threat from no fewer than two American species: the American crayfish Orconectes limosus and the Louisiana crayfishProcambarus clarkii, which were introducedfor commercial purposes or released accidentally.

Thanks to the collaboration of Maria Cristina Bruno from the Mach Foundation, which is involved in conservation efforts to protect the native crayfish, containment campaigns against invasive crayfish are carried out every year. In July 2026, the campaign focused on a number of ponds in the Valsugana, where the invasive crayfish were caught using special traps. The male crayfish caught are removed, whilst the females are sterilised. Several hundred individuals were captured over a period of about ten days. 

Glandular balsam

Among invasive plant species, the Himalayan balsam (Impatiens glandulifera) is the most threatening. An Asian species introduced for ornamental purposes, it is able to spread rapidly thanks to its rapid growth and efficient reproductive strategy. It manages to establish monospecific populations, displacing native plant species, partly due to the secretion of substances that inhibit the growth of other plants. Furthermore, the Himalayan balsam produces large quantities of nectar that is highly attractive to pollinating insects, and this can be detrimental to native species, which are visited less frequently.

Another negative aspect, observed in I. glandulifera but potentially applicable to other species as well, relates to the fact that when dense and extensive stands of these plants undergo physiological decline at the end of their annual cycle, they leave large bare patches on the banks of watercourses. The absence of riparian vegetation makes river banks more susceptible to erosion in autumn and winter, with the potential to exacerbate the impact of flooding.

Efforts to control this species have focused on the Palude di Roncegno and Fontanazzo protected areas in the municipality of Grigno, as it is particularly widespread in Valsugana. Given the plant’s particularly fragile root system, the best solution is manual removal, to be carried out before flowering, so that the uprooted plants can then be left in situ to decompose. The work has made it possible to reclaim around 5 hectares of previously infested areas, particularly damp undergrowth. Given the plant’s resilience and its ability to spread extensively through the soil, the work will likely need to be repeated in the coming years. However, the efforts made in 2026 have enabled the first phase of containment to be implemented, eliminating the largest clusters and preventing flowering and subsequent seed dispersal, with a view to achieving a more manageable situation in the coming years.

Like all interventions forming part of the Life NatConnect2030 project, this too is a development of the actions set out in the provincial PAF. The PAF – Prioritised Action Framework – is a multi-annual document that plans and monitors the actions necessary for the conservation of Natura 2000 habitats and species.