A striking feature of the Antarctic is the lack of diversity of vascular plants. Deschampsia antarctica Desv. and Colobanthus quitensis Bartl. have inhabited the maritime Antarctic for c. 5000 years. Pollen grains of both species and macroremains of the grass have been identified in mid-Holocene peat deposits on the South Shetland Islands (Birkenmajer et al. Reference Birkenmajer, Ochyra, Olsson and Stuchlik1985). However, there is no evidence from palaeorecords that any other vascular plants existed in this region during the Holocene, despite the fact that a major source of potential immigrants is located only 900 km to the north in Tierra del Fuego (Smith Reference Smith2003). With the current trend in regional warming in the maritime Antarctic (King et al. Reference King, Turner, Marshall, Conolley and Lachlan-Cope2003) and a growing number of visitors there is an increasing probability that plants, previously unable to flourish because of adverse climatic conditions, will be able to become established.
During our long-term botanical monitoring at King George Island we have recorded the appearance of a third vascular plant species, firstly only in the anthropogenic zone (Olech Reference Olech1996), but more recently in natural habitats. This is an alien species, annual meadow grass Poa annua L., which has currently colonized the moraines of the retreating Ecology Glacier (Fig. 1). Species usually associated with this habitat are the two native vascular plants, and mosses such as Bryum pseudotriquetrum (Hedw.) P. Gaertn., B. Mey. & Scherb. and Ceratodon purpureus (Hedw.) Brid.
Location of Poa annua in the vicinity of Polish Antarctic Station Arctowski. A = anthropogenic site, C = natural site (source: http://www.kgis.scar.org/).
Results and discussion
Poa annua L. has spread across areas in the vicinity of the Polish Antarctic Station Arctowski. The species was initially recorded in summer of 1985–86 (Olech Reference Olech1996). At Arctowski P. annua colonized places disturbed by human activities, where the soil structure was destroyed, preferring sites sheltered from the wind (Olech Reference Olech1996, Reference Olech1998). This anthropogenic population of P. annua was probably introduced by expeditioners either through soil from the greenhouse or with cargo or personal equipment. Poa annua flowers and sets seed successfully (Fig. 2) often a couple of times during the growing season and has a continuum of life-history types ranging from annual to long-lived perennial forms. Our genetic studies show high variability in the population around the station. This may be related to the increased human activity favouring probably several separate immigration events from different sources (Fig. 2) (Chwedorzewska Reference Chwedorzewska2008). In the summer 2008–09 an extensive population of P. annua was recorded in a new habitat (approximately 70 individuals on 100 m2), 1.5 km from the station on the deglaciated moraines of the Ecology Glacier (Fig. 1). The demographic study shows clearly that this population has been stable for at least two years. The most probable dispersal vector was the wind, which blows P. annua seeds from the station area.
Colonization of Poa annua in the Antarctic.
Poa annua has already colonized anthropogenic and natural habitats on most of the sub-Antarctic islands (e.g. Walton Reference Walton1975, Frenot et al. Reference Frenot, Gloaguen and Trehen1997), but in Antarctica it has occurred only temporarily in places strongly changed by human activity (e.g. Smith Reference Smith1996, Chwedorzewska Reference Chwedorzewska2009). For 25 years at Arctowski Station a large population of P. annua has grown, set seed and spread without any attempts to control it. The rapid regional warming in the South Shetland Islands (King et al. Reference King, Turner, Marshall, Conolley and Lachlan-Cope2003), has resulted in an amelioration of environmental conditions, which appear to have been sufficient to allow the successful establishment of this alien plant in natural habitats.
The Polish Antarctic Station is at present considering what might be done to solve the problem of Poa and what bio-security procedures are needed to avoid alien introductions in the future. This spread and persistence of P. annua highlights the need for constant vigilance against alien species in any cargo and personal effects, as well as in imported soil.
In Antarctica the start of an invasion has been recorded, and there are undoubtedly other aggressive alien species (P. annua is not yet displacing native species) which could be a serious threat to the terrestrial communities of indigenous organisms. Annex II of the Protocol on Environmental Protection to the Antarctic Treaty states clearly that non-indigenous species should be “disposed of by incineration or equally effective means that eliminates risk to native fauna or flora”. The main goal of this paper was to focus international attention on the problem of current invasions in Antarctic ecosystems due to the increasing of amelioration of environmental conditions and the systems needed to stop new introductions and exterminate established species (Hughes & Convey Reference Hughes and Convey2010).
Acknowledgements
The work was financed by the Ministry of Scientific Research and Higher Education grant IPY/27/2007. We thank the reviewers whose comments were most helpful in revising this paper.
