Non-indigenous flora of the Azores Archipelago (PT)
The 9 Azores islands are located in the North Atlantic Ocean, about 1500 km from Europe. The climate is temperate oceanic with a mean annual temperature of 17°C at sea level, and relative humidity is high as rainfall ranges from 1500 to 3000 mm. The proportion of non-indigenous vascular plants is 69% higher than in other island ecosystems, which has resulted from the removal of native vegetation and the introduction of many cultivated and ornamental plants, and from the relatively large extension of the agricultural landscape. The introduced plants were largely subcosmopolitan therophytes and hemicryptophytes, followed by chamaephytes. In contrast to Hawaii, vines are not significant weeds, probably a reflection of the temperate climate.
The families with highest absolute contributions were similar to those in other areas of the world (Poaceae, Asteraceae, Fabaceae, Brassicaceae, Scrophulariaceae). Many were introduced as ornamental or crop plants, but there were also many accidental introductions of weeds. About 55% of the non-indigenous taxa are considered weeds elsewhere. A somewhat unexpected result is the apparently reduced number of hybrid taxa, namely those resulting from crosses between native and exotic species of the same genus.
Considering the 9 islands, the percentage of introductions was positively correlated with human population density and island surface below 300 m, and negatively correlated to island surface allocated to natural areas, altitude and slope. Non-indigenous plants in the Azores occur not only in marginal habitats but also in a variety of different systems, from crops to stone walls, coastal and wooded areas, either native, planted or mixed.
Table of the non-indigenous plants in the Azores, in order of importance from highest to lowest (according to a random survey done on 529 sampling plots).
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Taxa
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Family
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Origin
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Situation
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Rubus inermis
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Rosaceae
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Europe
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It has invaded coastal wetlands.
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Pittosporum undulatum
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Pittosporaceae
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Australia
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It has invaded coastal halophytic systems and is one of the plants with the highest impact in the Azorean vegetation. It is able to overgrow native vegetation, forming pure stands and is very frequent and abundant in native woods of Myrica faya.
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Hedychium gardnerianum
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Zingiberaceae
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Himalaya
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It has invaded coastal halophytic systems and has the ability to completely replace native vegetation.
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Holcus lanatus
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Poaceae
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Europe
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It has invaded coastal wetlands.
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Mentha suaveolens
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Lamiaceae
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S. & W. Europe
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Found in pastures.
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Conyza bonariensis
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Asteraceae
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Tropical America
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|
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Selaginella kraussiana
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Selaginellaceae
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Tropical and Southern Africa
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|
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Tradescantia fluminensis
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Commelinaceae
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SE Brazil to Argentina
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Arundo donax
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Poaceae
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S. & C. Asia
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It has invaded large areas in coastal areas, threatening halophytic coastal meadows and dune vegetation. Initially used as a windbreak, it now dominates many cliffs near the coast. It is a major threat to water resources in California (US).
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Cryptomeria japonica
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Taxodiaceae
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C. & S. Japan
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Cyperus esculentus (EPPO list of invasive alien plants)
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Poaceae
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Mediterranean & SW Europe
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It has invaded coastal wetlands. It is a common weed of agricultural crops such as cornfields, vineyards and horticultural crops.
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Paspalum dilatatum
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Poaceae
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Brazil to Argentina
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|
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Acacia melanoxylon
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Fabaceae
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S.E. Australia, Tasmania
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Sporobolus indicus
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Poaceae
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Tropics & subtropics
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|
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Polygonum capitatum
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Polygonaceae
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Himalayas
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It has invaded coastal halophytic systems
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Phytolacca americana
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Phytolaccaceae
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N. America
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Erigeron karvinskianus
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Asteraceae
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Mexico
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Digitaria sanguinalis
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Poaceae
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S. & S.C. Europe
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It is a common weed of agricultural crops such as maize fields, vineyards and horticultural crops.
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Cynodon dactylon
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Poaceae
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W., S., S.E. & E.C. Europe
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It is frequent in coastal areas throughout the Archipelago, invading native communities on dunes.
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Trifolium repens (Fabaceae), Plantago lanceolata (Plantaginaceae), Hypochoeris radicata (Poaceae), Setaria pumila (Poaceae), Lolium perenne (Poaceae), Rumex obtusifolius ssp. obtusifolius (Polygonaceae), Prunella vulgaris (Lamiaceae), Lavatera cretica (Malvaceae), and Bromus willdenowii (Poaceae), all originating from Europe, where also listed among the most important non-indigenous plants in the Azores.
Other non-indigenous plants invading native coastal communities, including rocky coasts, are Carpobrotus edulis (Aizoaceae), Cyrtomium falcatum (Drypteridaceae), Mesembryenthemum spp. (Aizoaceae) and Aptenia cordifolia (Aizoaceae). Tamarix gallica (Tamaricaceae) is widely planted and is invading dunes and coastal wetlands. Ricinus communis (Euphorbiaceae), Petroselinum crispum (Apiaceae) and Tetragonia tetragonioides (Aizoaceae) have invaded coastal wetlands.
Moreover, Agave americana (Agavaceae), Clethra arborea (Clethraceae), Gunnera tinctoria (Gunneraceae), Leycesteria formosa (Caprifoliaceae), Opuntia ficus-indica (Cactaceae) and Ulex europaeus (Fabaceae) also seem to present a risk.
Hydrangea macrophylla (Hydrangeaeceae) is a woody species forming dense stands within native vegetation and abandoned pastures. Ailanthus altissima (Simaroubaceae, EPPO list of invasive alien plants) is a potential invader. Lantana camara (Verbenaceae) forms occasional dense stands. Solanum mauritianum (Solanaceae) is already common on several islands, although generally near human settlements. It forms dense stands in woods and along roads, trails and streams (see EPPO RS 2006/043).
Sources
Borges PAV, Cunha R, Gabriel R, Martins AF, Silva L, Vieira V (eds) (2005) A list of the terrestrial fauna (Mollusca and Arthropoda) and flora (Bryophyta, Pterophyta and Spermatophyta) from the Azores. Direcção Regional do Ambiente and Universitade dos Açores, Horta, Angra do Heroísmo and Ponte Delgada, 317 pp.
Silva L, Smith CW (2004) A characterization of the non-indigenous flora of the Azores Archipelago. Biological Invasions 6, 193-204
Silva L, Smith CW (2004) A quantitative approach to the study of non-indigenous plants: an example from the Azores Archipelago. Biodiversity and Conservation 15, 1661–1679
Tutin TG, Heywood VH, Burges NA, Moore DM, Valentine DH, Walters SM and Webb DA (1964/80) Flora Europeaea, Vol 1-5. Cambridge University Press, Cambridge.
Symposium on invasive plants in Ponte Delgada (Azores, Portugal)