populations, communities and potentially, ecosystem services (Taylor et al. 1993).
As shown before in this book, railways are mainly considered to be barriers for
wildlife or corridors for invasive species. However, railways are linear and almost
continuous patches of vegetation that penetrate into dense urban areas, ensuring a
structural connectivity. Despite their potential as corridors, railway verges functional connectivity has been poorly studied (but see Tikka et al. 2001), and most
studies have focussed on invasive species (Hansen and Clevenger 2005).
As mentioned previously, semi-natural grasslands are one of the vegetation types
in railway verges, especially in urban contexts, where the space is precious and the
verges have a reduced width. In general, semi-natural grasslands are important
habitats for conservation because they support plants, invertebrates and vertebrates,
including threatened ones, and provide ecosystem services (Ridding et al. 2015).
However, surfaces are decreasing all around Europe, therefore it is crucial to
conserve them and ensure connectivity between the patches to enhance gene and
species flows. In our study (Penone et al. 2012), we examined whether these areas
could provide functional connectivity for semi-natural grassland plants in urban
landscapes.
Using Structural Breaks to Detect Functional
Connectivity Along Railways
If linear structures provide functional connectivity an interruption of structure
should result in an interruption of the function. The structural connectivity of
railway verges is regularly interrupted by spatial breaks, such as overpasses and
stations. We hypothesised that if railway verges favour connectivity, spatially
connected communities within railway verges should be more similar than disconnected communities (H1). We tested this assumption by comparing floristic
dissimilarities between sites located along railway verges that were either connected
or separated by a railway break (Penone et al. 2012). In order to take into account
differences among plant species, we considered species traits linked to dispersal
abilities. These analyses were conducted on 71 plots located on two different
railway lines going from Paris to the south of the Paris region (Fig. 16.1).
We found a significant effect of railway breaks on most species and dispersal
traits consistent to our hypothesis (H1): connected communities were more similar
than disconnected ones, suggesting a potential corridor role of railway verges
(Penone et al. 2012). However, this effect was influenced by species mobility
(summarized in Fig. 16.2). Highly mobile species (e.g. wind pollinated) were not
affected by railway breaks, likely because they can disperse over long distances in
any direction. Similarly, we did not find a significant effect of railway breaks on
poorly mobile species (e.g. gravity-dispersed seeds). Their dispersal is more related
to very local factors (e.g. slope) and the effect of breaks might be only visible over
multiple generations. The most interesting result was found for moderately mobile
species (e.g. wind-dispersed seeds), for which we found a significant effect of
railway breaks. For these species railways seemed to provide functional
16 Ecological Roles of Railway Verges in Anthropogenic Landscapes …
267
As shown before in this book, railways are mainly considered to be barriers for
wildlife or corridors for invasive species. However, railways are linear and almost
continuous patches of vegetation that penetrate into dense urban areas, ensuring a
structural connectivity. Despite their potential as corridors, railway verges functional connectivity has been poorly studied (but see Tikka et al. 2001), and most
studies have focussed on invasive species (Hansen and Clevenger 2005).
As mentioned previously, semi-natural grasslands are one of the vegetation types
in railway verges, especially in urban contexts, where the space is precious and the
verges have a reduced width. In general, semi-natural grasslands are important
habitats for conservation because they support plants, invertebrates and vertebrates,
including threatened ones, and provide ecosystem services (Ridding et al. 2015).
However, surfaces are decreasing all around Europe, therefore it is crucial to
conserve them and ensure connectivity between the patches to enhance gene and
species flows. In our study (Penone et al. 2012), we examined whether these areas
could provide functional connectivity for semi-natural grassland plants in urban
landscapes.
Using Structural Breaks to Detect Functional
Connectivity Along Railways
If linear structures provide functional connectivity an interruption of structure
should result in an interruption of the function. The structural connectivity of
railway verges is regularly interrupted by spatial breaks, such as overpasses and
stations. We hypothesised that if railway verges favour connectivity, spatially
connected communities within railway verges should be more similar than disconnected communities (H1). We tested this assumption by comparing floristic
dissimilarities between sites located along railway verges that were either connected
or separated by a railway break (Penone et al. 2012). In order to take into account
differences among plant species, we considered species traits linked to dispersal
abilities. These analyses were conducted on 71 plots located on two different
railway lines going from Paris to the south of the Paris region (Fig. 16.1).
We found a significant effect of railway breaks on most species and dispersal
traits consistent to our hypothesis (H1): connected communities were more similar
than disconnected ones, suggesting a potential corridor role of railway verges
(Penone et al. 2012). However, this effect was influenced by species mobility
(summarized in Fig. 16.2). Highly mobile species (e.g. wind pollinated) were not
affected by railway breaks, likely because they can disperse over long distances in
any direction. Similarly, we did not find a significant effect of railway breaks on
poorly mobile species (e.g. gravity-dispersed seeds). Their dispersal is more related
to very local factors (e.g. slope) and the effect of breaks might be only visible over
multiple generations. The most interesting result was found for moderately mobile
species (e.g. wind-dispersed seeds), for which we found a significant effect of
railway breaks. For these species railways seemed to provide functional
16 Ecological Roles of Railway Verges in Anthropogenic Landscapes …
267