are open, ruderal vegetation (Artemisietea) usually occurs. Analyses of the complex
urban-rural gradient shows that urbanisation filters species in communities
depending on their adaptability to conditions in built-up areas (Cochard 2017). For
instance, kitchen gardens in urban areas may host species of the class Papaveretea
rhoeadis, but arable fields in rural areas host many more species. Epiphytic lichen
and bryophyte communities in cities, towns and villages occur on various kinds of
trees along streets, in gardens and parks. However, because of the reduced
air-quality, the relating communities in cities are often relatively species-poor in
comparison to lichen or bryophyte communities far away from cities and industries
in less polluted regions.
All these communities support species of various origin: apophytes (native) and
anthropophytes (foreign). Over time, both in the urban and in the rural areas, more
and more non-native species have spread (Simberloff et al. 2013; Aronson et al.
2014). At least 3.9% of all currently known vascular plant species of the global
vascular flora have become naturalized outside their natural ranges because of
humans, approximately equalling the size of the native European flora (van Kluenen
et al. 2015). A consequence of invasions is the possible decrease of native species
abundances, or even their replacement by non-native species (Martin-Albarracin
et al. 2015), although native species are not always threatened (e.g. Thomas and
Palmer 2015). In general, neophytes may invade urban areas, but there they do not
easily replace native species. But urban areas can function as a hub from where these
neophytes can spread into the rural areas (Kühn et al. 2017). There is usually a
gradient from very urbanised to very rural grid cells. In urban areas, there are specific
niches where non-native plant species may thrive and where native species may be
less competitive (e.g. Lososová et al. 2016). But outside the urban areas there is a
multitude of habitats which are less impacted and which may host not only native
plant species with a wider ecological amplitude but also with a small amplitude. In
some cases, these rural habitats may host endemic plant species. Indeed, the effects
of colonization of neophytes include homogenisation of both floras and habitats
(Olden 2006).
According to Connop and Nash (2018) “historically, aesthetics and recreation
have been the overriding drivers for urban green space design and management. This
has led to the simplification of habitats through frequent mowing, pruning of trees
and shrubs, removal of dead wood and mulching”. Ecologically driven practices
were not developed until much later (Wolschke-Bulmahn 1999). By selecting plants
based on beautification and easy thriving, cultivars and exotics were favoured over
native plants previously found in the original ecosystem. These kind of selecting
practices have been and are still being applied all over the world, putting pressure on
biodiversity and creating a kind of biotic homogenization of parks and gardens
(McKinney 2006; Groffman et al. 2014). In short, in too many urban environments
that lie in the same bioregion, one finds the similar immediately eye-catching
cultivars and exotics. In countries with intensive agriculture and livestock farming,
more and more species have come under pressure in rural areas. Today urban areas
may offer better options for some species than the rural area where they originally
thrived. Such urban sites can function as safe havens for specialist species that have
Urban Habitats: Cities and Their Potential for Nature Protection
433
urban-rural gradient shows that urbanisation filters species in communities
depending on their adaptability to conditions in built-up areas (Cochard 2017). For
instance, kitchen gardens in urban areas may host species of the class Papaveretea
rhoeadis, but arable fields in rural areas host many more species. Epiphytic lichen
and bryophyte communities in cities, towns and villages occur on various kinds of
trees along streets, in gardens and parks. However, because of the reduced
air-quality, the relating communities in cities are often relatively species-poor in
comparison to lichen or bryophyte communities far away from cities and industries
in less polluted regions.
All these communities support species of various origin: apophytes (native) and
anthropophytes (foreign). Over time, both in the urban and in the rural areas, more
and more non-native species have spread (Simberloff et al. 2013; Aronson et al.
2014). At least 3.9% of all currently known vascular plant species of the global
vascular flora have become naturalized outside their natural ranges because of
humans, approximately equalling the size of the native European flora (van Kluenen
et al. 2015). A consequence of invasions is the possible decrease of native species
abundances, or even their replacement by non-native species (Martin-Albarracin
et al. 2015), although native species are not always threatened (e.g. Thomas and
Palmer 2015). In general, neophytes may invade urban areas, but there they do not
easily replace native species. But urban areas can function as a hub from where these
neophytes can spread into the rural areas (Kühn et al. 2017). There is usually a
gradient from very urbanised to very rural grid cells. In urban areas, there are specific
niches where non-native plant species may thrive and where native species may be
less competitive (e.g. Lososová et al. 2016). But outside the urban areas there is a
multitude of habitats which are less impacted and which may host not only native
plant species with a wider ecological amplitude but also with a small amplitude. In
some cases, these rural habitats may host endemic plant species. Indeed, the effects
of colonization of neophytes include homogenisation of both floras and habitats
(Olden 2006).
According to Connop and Nash (2018) “historically, aesthetics and recreation
have been the overriding drivers for urban green space design and management. This
has led to the simplification of habitats through frequent mowing, pruning of trees
and shrubs, removal of dead wood and mulching”. Ecologically driven practices
were not developed until much later (Wolschke-Bulmahn 1999). By selecting plants
based on beautification and easy thriving, cultivars and exotics were favoured over
native plants previously found in the original ecosystem. These kind of selecting
practices have been and are still being applied all over the world, putting pressure on
biodiversity and creating a kind of biotic homogenization of parks and gardens
(McKinney 2006; Groffman et al. 2014). In short, in too many urban environments
that lie in the same bioregion, one finds the similar immediately eye-catching
cultivars and exotics. In countries with intensive agriculture and livestock farming,
more and more species have come under pressure in rural areas. Today urban areas
may offer better options for some species than the rural area where they originally
thrived. Such urban sites can function as safe havens for specialist species that have
Urban Habitats: Cities and Their Potential for Nature Protection
433