The invasion of the senecios

Senecios are plants of the genus Senecio and the same family as daisies (Asteraceae), which are widespread throughout the Iberian Peninsula. Many of them are native, but some are species recently introduced by humans and have become invasive. This is the case with Senecio inaequidens, well known for its spread in the pastures of the Pyrenees and because it is toxic to livestock, but also with Senecio pterophorus, which has recently proliferated in many natural areas along the coast and pre-coast.

“ In the Llobregat Delta, we're seeing an explosion of flowering Senecio pterophorus , but that's not the only place where we can find it. Since the early 1990s, it has been spreading through the channels and floodplains of the Llobregat and Besòs rivers, reaching several natural areas such as Montseny and Montnegre-Corredor,” explains Joan Pino, director of CREAF and coordinator of the Catalan exotic and invasive species monitoring initiative, EXOCAT.

Although the most publicized of the senecios that have invaded Catalonia is Senecio inaequidens, mainly due to the problems with high-mountain farmers, there are also two species of senecio currently impacting the Barcelona Metropolitan Region. They are Senecio ptherophorus and Senecio angulatus. Both bloom in spring and are originally from South Africa. " The introduction of senecio to the Iberian Peninsula is caused by human activity , which probably introduced it in the form of seeds hidden in wool from Africa and transferred it to rivers through the washing of this material," according to Pino.

Senecio pterophorus is a shrub species first found in Catalonia in the early 1980s. Since then, it has expanded significantly in coastal and pre-coastal areas, then spread to many neighboring mountain ranges. This senecio has now made a significant entrance into protected areas such as Collserola, Montnegre-Corredor, and Montseny, among others .

Another species found in the metropolitan region is Senecio angulatus, a climbing plant with fleshy leaves that seems to prefer warm climates. It is especially prevalent along the coast and shoreline, and is already a problem in areas such as Montjuïc, the southern slopes of Collserola, and the shores of Garraf .

"The main problems with invasive senecios are that they can compete with native flora, especially for certain resources such as pollinators, since they have a fairly long flowering period and are very resilient species ," the ecologist points out.

Senecio inaequidens is also native to southern Africa and has therefore adapted easily to the temperate climates found in the Mediterranean. Specifically, it has spread with a certain preference to mid-mountain areas and, to a lesser extent, to lowlands, especially along the banks of some rivers.

However, in recent years, given increasingly mild winter temperatures, it has spread significantly in mountain areas and has impacted livestock farming, as it is toxic to livestock . Furthermore, it affects the ecosystem and could jeopardize the conservation of Pyrenean grasslands, which are a true haven of biodiversity. Currently, Senecio inaequidens is locally abundant in northeastern Catalonia and is found in isolation in some areas of the Basque Country, Asturias, and eastern Castile and León.

This plant has also reached some of the pilot areas of the European Life Pyrenees4Clima project , an initiative that seeks to adapt the Pyrenees region to climate change, coordinated by the Pyrenean Observatory of Climate Change (OPCC) of the Pyrenees Working Community (CTP) and co-financed by the European Union, in which CREAF participates as a partner. One of these affected pilot areas is located in the Albera Natural Park , an area dominated by Mediterranean holm oak forests with open spaces where cows and goats graze. It is also affecting another pilot area in Cerdanya.

“Currently, the project, together with the UAB School of Veterinary Medicine, is evaluating whether Senecio poses a risk to the pilot area, either due to its ability to impoverish the forage value of natural pastures or due to its potential effects on livestock. We also want to identify the most effective forest, livestock, and pasture management methods for controlling its spread,” explains Diana Pascual, a CREAF researcher and project member.

So what do we do about this array of Senecios spreading across the country? According to Pino, " we can try to control them in some particularly valuable areas, where there are interesting habitats or in protected areas, but we can't do anything more than this ." The reason is that, once a species has established itself in an ecosystem and is in the midst of colonization, it is very difficult and expensive to eradicate. Furthermore, Senecio inaequidens has a great capacity for dispersal, both spatially (the seeds are very well dispersed by the wind) and temporally (the seeds remain dormant for long periods until they have a chance to germinate). The only way to eliminate them is to uproot them directly , because they are resistant to herbicides, which, moreover, are not a recommended option in habitats such as grasslands and mountain meadows. That's why efforts must be focused on the prevention and monitoring phases for the arrival of invasions .

In this regard, at CREAF we have led the development of two lists—the black list (more urgent) and the red list—of the most dangerous species that could enter Catalonia and which require priority work. We have done this within the framework of the EXOCAT project, which has been studying all of Catalonia's exotic species for over 10 years, and in particular those that are becoming invasive.