Abstract
Ornamental plants are an important component of urban floras and a significant source of alien plant invasions to the surrounding landscapes. We studied ornamental flora across 174 settlements in the Czech Republic, Central Europe. The aims of the study were to (i) identify clusters of sites that are defined as distinctive groups of ornamental taxa reflecting environmental or socioeconomic factors and (ii) apply the classification approach which is traditionally used for spontaneous vegetation in order to evaluate the potential of different settlement types to act as source sites of invasive species. The inventories were classified in a similar manner that is generally applied to spontaneous vegetation using the COCKTAIL method. Diagnostic taxa were classified in a repeatable manner into 17 species groups, forming five distinctive clusters with ~70% of sites attributed to one cluster. The species pools of the clusters differed in their representation of species with native or alien status and different life forms. The following clusters were distinguished, based on the prevailing type of settlement: (1) old villas neighbourhoods of towns, (2) upland settlements, (3) modern neighbourhoods, (4) old rustic settlements and (5) modern rustic settlements. Similar to spontaneous vegetation, the classification of ornamental flora reflects both basic natural gradients (i.e. altitude) and man-made factors (i.e. the preferences for certain plants and associated management practices). Alien taxa associated with modern neighbourhoods are characterised by a relatively higher invasion potential than those from, for example, old rustic settlements. This is especially true for woody species which can spread in ruderal habitats as a result of urban sprawl. Our results showed that the classification method, commonly used to analyse vegetation data, can also be applied to ornamental flora.
Highlights
IntroductionThe recent increase in the knowledge of alien floras in countries worldwide (e.g. Pyšek et al 2012, 2017; van Kleunen et al 2015), as well as in the theory of biological invasions (e.g. Catford et al 2009; Blackburn et al 2011; Kueffer et al 2013; Enders et al 2019) has drawn the attention of researchers, amongst other topics, towards the ecological consequences of ornamental introductions (e.g. Thompson et al 2003; Gaston et al 2005, 2007; Smith et al 2006; Loram et al 2008a; van Heezik et al 2013; Hulme et al 2018; van Kleunen et al 2018)
Ornamental plants represent an important component in the urban space (Chocholoušková and Pyšek 2003; Kowarik 2005; Botham et al 2009; Pyšek and Chytrý 2014; Pergl et al 2016b), as well as a significant source of invasive species as a result of escapes from private or public gardens (Reichard and White 2001; DehnenSchmutz et al 2007; Hanspach et al 2008; Hulme 2011; Pyšek et al 2011; Gregor et al 2012)
No reasonable pattern was found in the remaining cluster, which includes 55 sites (i.e. 32% of all sampled sites). This cluster was characterised as an unspecific ornamental flora, since no potential subgroup was sufficiently pronounced in its composition, habitat demands and cultural indication
Summary
The recent increase in the knowledge of alien floras in countries worldwide (e.g. Pyšek et al 2012, 2017; van Kleunen et al 2015), as well as in the theory of biological invasions (e.g. Catford et al 2009; Blackburn et al 2011; Kueffer et al 2013; Enders et al 2019) has drawn the attention of researchers, amongst other topics, towards the ecological consequences of ornamental introductions (e.g. Thompson et al 2003; Gaston et al 2005, 2007; Smith et al 2006; Loram et al 2008a; van Heezik et al 2013; Hulme et al 2018; van Kleunen et al 2018). Many taxa initially escape and spread in spatially restricted areas in the surroundings of gardens and spread and colonise more distant vegetation Such naturalisation foci may appear as a result of the combined effects of local popularity of a given taxon, regardless of its invasion status (Humair et al 2014), suitable natural and cultural conditions (Marco et al 2010), abundant propagation in cultivation and easy semi-spontaneous establishment in gardens. Many ornamental taxa become naturalised or even invasive in peri-urban belts or along motorways (Yang et al 2015) This implies that (i) most naturalised ornamentals come from populations that are already pre-adapted to the local conditions (Mack 2000; Pyšek et al 2011), (ii) the naturalised taxa are not distributed evenly across various natural and cultural gradients, but they are concentrated in specific conditions which are generally favourable for many escaping taxa and (iii) where there is a suitable set of introduction pathways and dispersal vectors (von der Lippe and Kowarik 2007; Wilson et al 2009)
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