Exotic plant species in Islas Baleares, Spain
A list of exotic vascular plants which have been introduced in to the Islas Baleares (Spain) has been elaborated, identifying the most dangerous species. So far, about 305 introduced species have been identified, representing 15.9 % of the total Balearic flora.
The most frequent origin of alien plants was America (31.8 %), followed by the Mediterranean basin (18.4%) and Africa (16.4%). The most frequent life forms of these exotic species are phanerophytes (34.4%), followed by annual herbaceous species (therophytes) (29.5%). This pattern is disharmonic when compared with the indigenous flora which is characterized by a scarcity of phanerophytes (8.4%), especially trees, and a large proportion of therophytes (41.3%). Trees and other large species were most likely introduced for a specific use (ornamental, medicinal, forestry), while most annual species probably arrived as contaminants of crop seeds.
The document “Els vegetals introduïts a les Illes Balears” gives information about the main invasive plants of the Islands: Agave americana, Ailanthus altissima (EPPO List of Invasive Alien plants), Aloe spp., Amaranthus spp., Arundo donax, Aster squamatus, Carpobrotus spp., Chamaesyce spp., Conyza spp., Cyperus alternifolius, Disphyma crassifolium, Ipomoea indica, Nicotiana glauca, Opuntia maxima, Oxalis pes-caprae, Paspalum paspalodes, Ricinus communis, Senecio cineraria, Solanum bonariense, Soliva stolonifera, Sorghum halepense, Spartium junceum, Trapeolum majus.
Potentially invasive plants are also listed: Abutilon theophrasti, Acacia spp., Aeonium arboretum, Anredera cordifolia, Artemisia arborescens, Bromus catharticus, Clematis vitalba, Coronopus didymus, Cortaderia selloana, Cotula coronopifolia, Datura spp., Echinochloa colona, Gomphocarpus fruticosus, Helianthus tuberosus, Kalanchoe daigremontiana, Lantana camara, Limoniastrum monopetalum, Lonicera japonica, Melia azedarach, Mesembryanthemum crystalllinum, Mirabilis jalapa, Myoporum tenuifolium, Nothoscordum borbonicum, Parkinsonia aculeate, Pennisteum spp., Phytolacca americana, Pittosporum tobira, Retama sphaerocarpa, Robinia pseudoacacia, Senecio angulatus, Setaria parviflora, Solanum linnaenum, Stenotaphrum secundatum, Xanthium spp.
A study done on Mallorca shows that 15.9% of the total island flora consists of naturalised or sub-spontaneous species, but only 9.5% could be considered as naturalised in a very broad sense. Mediterranean ecosystems are resistant to the invasion of exotic species, but it is also likely that there is a certain under-estimation of these species since many of them, of Mediterranean origin, could have been introduced by humans in very ancient times. The most sensitive environments to invasion of exotic species are, in order of importance: roadsides, dry river beds, crop fields, and to a lesser extent rocky coasts, wetlands and dune systems. On Mediterranean islands, the most mature, stable environments seem to be extremely resistant to invasion, whereas the open and/or permanently disturbed habitats are the most susceptible to invasion by exotic species.
Moragues E, Rita J (2006) Exotic plant species in the Balearic Islands, Spain. In: Invasive plants in Mediterranean Type Regions of the World (Ed. by S Brunel). Council of Europe publishing. Strasbourg. p. 324.
Moragues E, Rita J (2006) Habitat distribution of exotic plant species on Mallorca Island. In: Invasive plants in Mediterranean Type Regions of the World (Ed. by S Brunel). Council of Europe publishing. Strasbourg. p. 349.
Moragues Botey E, Rita Larrucea J (2005) Els vegetals introduïts a les Illes Balears. Documents tècnics de conservació. II època, núm.11.Govern de les Illes Balears. 126 p. http://herbarivirtual.uib.es/documents/publicaciones/llibre_exotiques.pdf