differently. In some cases, low soil water availability reduces their invasiveness
(Alpert et al. 2000; Stohlgren et al. 2001), while some other alien species can
tolerate drought better than local species (Williams and Black 1994; Milchunas and
Lauenroth 1995; Nernberg and Dale 1997). In the latter case, such aliens might
extend their range boundaries. Drought might have a particular effect on increased
invasibility of fast-growing alien species if habitats are un-shaded (Schumacher
et al. 2008).
Another recognised impact of global warming is the shift in plant phenology
caused by an earlier biological spring and a delayed winter; while again, these
effects will vary according to water availability and regional characteristics
(Pen ˜uelas et al. 2009). The lengthened vegetation period might represent additional
benefits for invasive species in the Mediterranean, since these are mostly species
which flower late and their flowering period is terminated by oncoming winter. The
end of flowering in late season is one of the significant differences between native
and non-native species in general (Knapp and Ku ¨hn 2012). Similarly, growth and
biomass accumulation in non-natives are terminated by the first occurring low
temperatures and are not ended gradually by plant senescence, as in most native
species. This should be especially important for annual species.
Thorough studies are needed to better predict whether any alien species that are
currently regarded as non-invasive non-native species and are already present could
benefit from global change and turn into invasive alien species. This is why every
alien species must be taken into consideration. In this chapter we discuss whether
global warming might favour the non-invasive alien Aster squamatus, which is
already present and whether it could potentially become invasive.
19.2 Aster squamatus, a Non-invasive Alien in Slovenia
Aster squamatus (Sprengel) Hieron. is a hemicryptophyte originating from central
South America, occupying habitats like salt marsh landscapes from Central
Argentina (Cantero et al. 1998). Even though A. squamatus does not usually form
large dense stands in introduced habitats, the species is distributed widely in many
European countries, among them Italy (Pace and Tammaro 2001), Spain (Molina
et al. 2004), France (Bassett 1980), Malta (Deidun 2010), Cyprus (Hand 2000), and
Greece (Theocharopoulos et al. 2006).
The first record of A. squamatus in Slovenia was noted in 1973 (Wraber 1982),
and the species has been constantly present since then, although not highly invasive
(Kaligaric ˇ 1998; Glasnovic ´ 2006). This species has also been observed in urban
areas (urbanophile species) like the old town centre of Izola. Even though it is not
highly invasive, where present, its occurrence is disturbing, especially near the two
most important coastal wetlands along the Slovenian coast: Sec ˇovlje salina and
S ˇ kocjan inlet, representing various Natura 2000 habitats. Sec ˇovlje salina is a
traditionally built salt-pan system where active salt-making is still partly practised.
The salt-pan system includes natural salt pools (flooded and dried out), which are
280
N. S ˇ ajna et al.
(Alpert et al. 2000; Stohlgren et al. 2001), while some other alien species can
tolerate drought better than local species (Williams and Black 1994; Milchunas and
Lauenroth 1995; Nernberg and Dale 1997). In the latter case, such aliens might
extend their range boundaries. Drought might have a particular effect on increased
invasibility of fast-growing alien species if habitats are un-shaded (Schumacher
et al. 2008).
Another recognised impact of global warming is the shift in plant phenology
caused by an earlier biological spring and a delayed winter; while again, these
effects will vary according to water availability and regional characteristics
(Pen ˜uelas et al. 2009). The lengthened vegetation period might represent additional
benefits for invasive species in the Mediterranean, since these are mostly species
which flower late and their flowering period is terminated by oncoming winter. The
end of flowering in late season is one of the significant differences between native
and non-native species in general (Knapp and Ku ¨hn 2012). Similarly, growth and
biomass accumulation in non-natives are terminated by the first occurring low
temperatures and are not ended gradually by plant senescence, as in most native
species. This should be especially important for annual species.
Thorough studies are needed to better predict whether any alien species that are
currently regarded as non-invasive non-native species and are already present could
benefit from global change and turn into invasive alien species. This is why every
alien species must be taken into consideration. In this chapter we discuss whether
global warming might favour the non-invasive alien Aster squamatus, which is
already present and whether it could potentially become invasive.
19.2 Aster squamatus, a Non-invasive Alien in Slovenia
Aster squamatus (Sprengel) Hieron. is a hemicryptophyte originating from central
South America, occupying habitats like salt marsh landscapes from Central
Argentina (Cantero et al. 1998). Even though A. squamatus does not usually form
large dense stands in introduced habitats, the species is distributed widely in many
European countries, among them Italy (Pace and Tammaro 2001), Spain (Molina
et al. 2004), France (Bassett 1980), Malta (Deidun 2010), Cyprus (Hand 2000), and
Greece (Theocharopoulos et al. 2006).
The first record of A. squamatus in Slovenia was noted in 1973 (Wraber 1982),
and the species has been constantly present since then, although not highly invasive
(Kaligaric ˇ 1998; Glasnovic ´ 2006). This species has also been observed in urban
areas (urbanophile species) like the old town centre of Izola. Even though it is not
highly invasive, where present, its occurrence is disturbing, especially near the two
most important coastal wetlands along the Slovenian coast: Sec ˇovlje salina and
S ˇ kocjan inlet, representing various Natura 2000 habitats. Sec ˇovlje salina is a
traditionally built salt-pan system where active salt-making is still partly practised.
The salt-pan system includes natural salt pools (flooded and dried out), which are
280
N. S ˇ ajna et al.