New record: Galenia pubescens in Spain
Galenia pubescens (Aizoaceae) is a prostrate perennial plant native to South Africa where it colonizes inland karoo vegetation (arid vegetation composed of dwarf, succulent shrubs mainly belonging to the families Mesembryanthemaceae, Crassulaceae and Asteraceae, and constituing a hotspot of biodiversity) and coastal areas (between altitudes of 15 to 1830 m). G. pubescens has been introduced either voluntarily or accidentally and naturalized in other Mediterranean Types regions: in Southern Australia, in Chile, in California and in the Mediterranean Basin (Israel and Southern Spain). Nevertheless, it is not included in national lists of invasive alien plants, as it is known to colonize mainly disturbed environments.
G. pubescens was recently recorded in Andalucía (Southern Spain) in 3 coastal areas in Huelva, Cádiz and Málaga. Its potential invasiveness has been assessed both in salty wetlands and dunes by analyzing the following factors:
Time since introduction in Spain: it is estimated that the species has been present in Spain for at least 40 years and that it currently covers 15;804 ha.
Growth type: in dunes and wetlands, G. pubescens was the only perennial species forming dense prostrate mats.
Flowering and seed production: in coastal dunes, G. pubescens flowered throughout the year. Annual seed production in dunes was estimated around 100;000 seeds/m²/year. The flowering period of G. pubescens was longer than the one measured for the invasive Carpobrotus edulis (Aizoaceae, EPPO List of Invasive Alien Plants) in Californian coastal areas, and the amount of seeds produced was about 4 times higher. Additionally, the small seeds produced by G. pubescens are rapidly spread along transport corridors such as road sides were the plant is usually found. Further studies on seed persistence and germination should be done.
Light attenuation: specific light attenuation values measured for G. pubescens were 98.3-99.6%, and were significantly higher than those measured for any other species in dunes and in wetlands.
Overlapping with flowering period of native species: the flowering period of G.;pubescens was the longest among dune plant species. Percentage of overlap reached mean values of 94±10% in dunes, and 73±38% in wetlands.
Loss of native species richness and diversity: a significant decrease in the native species richness and Shannon’s diversity index was found in the invaded plots of both dunes and wetlands. The loss of native richness and diversity persisted in all seasons. These indices were higher than those reported for Carpobrotus edulis invading Mediterranean islands.
Changes in plant functional types in invaded dunes: perennial species were substituted by annual, ruderal grasses or forbs such as Bromus spp. (Poaceae), Ecballium elaterium (Cucurbitaceae), Anacyclus radiatus (Asteraceae) as well as the invasive Oxalis pes-caprae (Oxalidaceae, EPPO List of IAP). In wetlands, changes were less evident as the contribution of ruderal species was already relatively high.
From the analysis of all these factors, it could be concluded that G. pubescens has a competitive advantage over native vegetation. Monitoring and control measures to prevent the spread of this species are therefore recommended.
Sources
Garcia-de-Lomas J, Cozar A, Dana ED, Hernandez I, Sanchez-Garcia I, Garcia CM (2010) Invasiveness of Galenia pubescens (Aizoaceae): a new threat to Mediterranean-climate coastal ecosystems. Acta Oecologica 36(1), 39-45.
Euekalert Website (2010) Exotic plant takes over dunes of Southern Spain. http://www.eurekalert.org/pub_releases/2010-03/f-sf-ept032910.php
El Mundo (2010) Una planta exótica invade las dunas costeras del sur de España. El Mundo, 2010/03/29. http://www.elmundo.es/elmundo/2010/03/29/ciencia/1269869021.html