effect on communities through habitat size reduction and dispersal limitation. All
these effects should be reflected in communities’ trait composition (Weiher and
Keddy 1999). While the first abiotic effects (temperature, nitrogen), should not be
influenced by connectivity between patches within urban landscapes, the seconds
(fragmentation effects) should be attenuated if communities are connected. We used
this assumption as a supplementary and indirect approach to assess functional
connectivity in railway verges. We hypothesised that if railway verges favour
connectivity this should attenuate the effect of fragmentation on plant communities
(H2). We thus examined the effects of urbanisation on species richness, diversity
and trait composition in railway verges and compared our results with the patterns
described in literature. This study was conducted using the same data as the previous analysis, i.e. 71 plots on two lines.
We did not detect urbanisation effects on plant communities due to fragmentation (Penone et al. 2012). Indeed, we did not find significant relationships between
urban cover and plant richness, diversity or dispersal traits, while most studies
detected positive or negative effects, depending on urbanisation intensity
(McKinney 2008). In contrast we found an effect of abiotic conditions linked to the
urban landscape, which were consistent with the literature. For instance, we
detected a positive effect of urbanisation on the abundance of species adapted to
higher temperatures and nitrogen levels (Penone et al. 2012). These results matched
our hypothesis (H2) and thus further suggested that railway verges provide functional connectivity in urban landscapes for semi-natural grassland species.
What About Exotic and Invasive Species?
Our study showed that railway verges can play a positive role for semi-natural
grassland plants in urban landscapes by connecting communities and potentially
improving gene and species flow between communities (Penone et al. 2012).
However, as showed in Chap. 5, railway verges can also be corridors for invasive
species. In order to explore this topic in an urban context, we performed the same
analyses described above (railway breaks and urbanisation effects) separately for
exotic and invasive species (Penone et al. 2012). We also focussed on one particular
invasive species, Senecio inaequidens, which is one of Europe’s fastest plant
invaders and is suspected to spread along railways (Lachmuth et al. 2010).
We detected a significant effect of railway breaks on community similarity in
terms of exotic but not invasive species (the latter being a subset of the exotic). As
for native plants, this effect was only observed for overpasses and not railway
stations (Penone et al. 2012). In addition, we measured the similarity between plots
in the two different railway lines, accounting for urbanisation effects. We also found
a difference between the two lines for exotic but not for invasive species (Penone
et al. 2012). According to our hypothesis (H1: if railways verges provide functional
connectivity, structurally connected communities should be more similar than
disconnected ones) this result suggests that railway verges might play a connectivity role for exotic but not for invasive species in urban landscapes.
16 Ecological Roles of Railway Verges in Anthropogenic Landscapes …
269
these effects should be reflected in communities’ trait composition (Weiher and
Keddy 1999). While the first abiotic effects (temperature, nitrogen), should not be
influenced by connectivity between patches within urban landscapes, the seconds
(fragmentation effects) should be attenuated if communities are connected. We used
this assumption as a supplementary and indirect approach to assess functional
connectivity in railway verges. We hypothesised that if railway verges favour
connectivity this should attenuate the effect of fragmentation on plant communities
(H2). We thus examined the effects of urbanisation on species richness, diversity
and trait composition in railway verges and compared our results with the patterns
described in literature. This study was conducted using the same data as the previous analysis, i.e. 71 plots on two lines.
We did not detect urbanisation effects on plant communities due to fragmentation (Penone et al. 2012). Indeed, we did not find significant relationships between
urban cover and plant richness, diversity or dispersal traits, while most studies
detected positive or negative effects, depending on urbanisation intensity
(McKinney 2008). In contrast we found an effect of abiotic conditions linked to the
urban landscape, which were consistent with the literature. For instance, we
detected a positive effect of urbanisation on the abundance of species adapted to
higher temperatures and nitrogen levels (Penone et al. 2012). These results matched
our hypothesis (H2) and thus further suggested that railway verges provide functional connectivity in urban landscapes for semi-natural grassland species.
What About Exotic and Invasive Species?
Our study showed that railway verges can play a positive role for semi-natural
grassland plants in urban landscapes by connecting communities and potentially
improving gene and species flow between communities (Penone et al. 2012).
However, as showed in Chap. 5, railway verges can also be corridors for invasive
species. In order to explore this topic in an urban context, we performed the same
analyses described above (railway breaks and urbanisation effects) separately for
exotic and invasive species (Penone et al. 2012). We also focussed on one particular
invasive species, Senecio inaequidens, which is one of Europe’s fastest plant
invaders and is suspected to spread along railways (Lachmuth et al. 2010).
We detected a significant effect of railway breaks on community similarity in
terms of exotic but not invasive species (the latter being a subset of the exotic). As
for native plants, this effect was only observed for overpasses and not railway
stations (Penone et al. 2012). In addition, we measured the similarity between plots
in the two different railway lines, accounting for urbanisation effects. We also found
a difference between the two lines for exotic but not for invasive species (Penone
et al. 2012). According to our hypothesis (H1: if railways verges provide functional
connectivity, structurally connected communities should be more similar than
disconnected ones) this result suggests that railway verges might play a connectivity role for exotic but not for invasive species in urban landscapes.
16 Ecological Roles of Railway Verges in Anthropogenic Landscapes …
269