Invasive alien plants in Cap de Creus and Costa Brava
Cat’s claw, the prickly pear cactus and gazania are the invasive alien plants showing the greatest impact on the Cap de Creus and Costa Brava cliffs.
Through the LIFE medCLIFFS project, a series of adapted techniques will be developed to eradicate and control some of the populations of these three species in both in public areas and in private gardens of the Cap de Creus Natural Park and its surrounding area.
Description
Its common name cat’s claw comes from the shape of its leaves, which remind the claws of a cat. This plant has evergreen, fleshy leaves, which are triangular in section, and opposite to each other. It has large flowers up to 10 cm in diameter, pink to purple, and its fruits are fleshy inside and edible. It blooms from late spring to late summer. This plant can reproduce sexually, by pollination by insects and fruit generation, or asexually, by spreading its branches along the substrate, forming a carpet, and generating new individuals by means of stolons. Given that this plant grows horizontally, it does not usually exceed 20 cm in height.
Distribution
This plant is native to South Africa and can be found on the Costa Brava forming large carpets next to build up areas, where it has jumped over fences and has managed to colonise natural ecosystems. It can grow on beaches and sandy soil, as well as on rocky shores, pine groves and scrubland areas.
Issues
The main driver of the spread of this plant is people. Intentionally planted for landscaping and slope containment, it can spread rapidly and cover the entire substrate forming dense carpets that prevents other plant species from developing. Furthermore, it has the ability to generate new individuals from cuttings or plant pieces that are able to generate new roots. Also, it is not very demanding in terms of substrate and nutrients, and can grow even in poor soils. Besides, its eye-catching flowers attract more pollinating insects, preventing them from pollinating native plant species. Due to its big and bright coloured flowers, the cat’s claw is highly appreciated for its aesthetic value and is not perceived as a threat to natural habitats.
Description
The prickly pear cactus is a shrub with fleshy, spade-shaped stems covered with thorns. This plant can reproduce asexually, as the fragments from the mother plant can root and form a new individual. However, this species can also reproduce by seed, once it has been pollinated by insects. The seeds are scattered by animals such as lizards, and can remain dormant and retain their capacity to germinate until the right conditions are met, with temperatures of around 21 °C. The seedlings tend to grow rapidly during the summer months, with high viability rates due to their resistance to drought, which ensures the success of this species in invaded coastal areas.
Distribution
Originally from semi-arid habitats in Central America, it arrived in Europe in the mid-16th century through the Spanish conquerors. It was introduced intentionally for agricultural cultivation, as it was used to produce cochineal, the source of the carmine pigment. Prickly pears cactuses were also grown for its fruits, used for human consumption. The species has also been used as an ornamental plant and to form protective plant fences in arid areas. In Costa Brava it is widespread in areas with intense human activity: next to housing developments, under power lines, etc., as well as in slashed areas, where these plants have been cut into pieces from which new individuals have been able to grow.
Issues
The rapid development and drought resistance shown by prickly pears give them advantages when competing with native plant species. In addition, these invasive plant species can affect the habitat of the invaded areas, thus modifying the availability of resources such as light, water and nutrients or minerals, among others. Therefore, the presence of prickly pear cactuses alters the structure and abundance of native and endemic species, which become displaced and cannot regenerate. The thorns of these plants are also a danger, as they can cause damage to wildlife as well as those animals that eat young stems.
On footpaths where prickly pears are widespread, they make it difficult for people to pass and can even cause damage.
Description
It is a low-growing herb that grows on sandy soils, at ground level, and reaches a height of 20-50 cm. Flowers can have different colours (usually a bright orange or yellow) or different colouring patterns depending on the variety. These flowers open up on sunny days, while they remain closed at night and on cloudy days. They are resistant to drought and lack of nutrients, so they can easily grow on any type of soil and form a thick carpet.
Distribution
It is a species of herbaceous plant from South Africa and Mozambique. It was introduced for ornamental purposes and for slope protection.
Issues
It is a new species in our region and is not yet listed in any legislation, but it is showing highly aggressive invasive behaviour due to a very effective propagation system, which threatens some of the most important populations of Limonium geronense, Limonium tremolsii and Seseli farrenyi. Gazania can easily reproduce from cuttings and each flower produces hundreds of seeds that are dispersed with the help of the wind, which causes it to expand rapidly.
Its ability to cover the substrate quickly and its low water requirements give it a competitive advantage over native plants, eventually displacing them. As with Carpobrotus edulis (cat’s claw), its invasive potential is increased by the fact that this species is highly appreciated for its aesthetic value, so people do not perceive the danger it poses to the habitat conservation.
Cat’s claw, prickly pear cactus and gazania are the most problematic invasive plants in Cap de Creus, but there are around thirty other species of exotic flora that can have a negative impact on the Mediterranean cliffs of the Costa Brava.
You can find out about the rest of the invasive and potentially invasive alien plant species of the Costa Brava on the Invasive flora page and consult their data sheets on the Resources page.
The first step to correctly manage exotic flora is to know where the species grow and how their populations evolve over time. For this reason, the LIFE medCLIFFS project has created two participatory networks for the early detection and monitoring of invasive plant populations on the Costa Brava and Cap de Creus: the LIFE medCLIFFS Observers Network and the LIFE medCLIFFS Volunteers Network.
