Challenge G: An even more competitive and cost efficient railway

Railway edges, ecological corridors: how to conciliate biodiversity and economic management of vegetation?

Author: Caterina Penone1,2, 3

1 SNCF INFRA/IG-LG-ENV - 6, Avenue François Mitterrand - 93574 La Plaine St Denis - France 2 SNCF INFRA/CSC ER IM 1 - 18, Rue Dunkerque - 75010 Paris - France 3 MNHN UMR7204 CERSP – 61, Rue Buffon - CP 53 - 75004 Paris - France

1 Challenge G: An even more competitive and cost efficient railway

Introduction

Today biodiversity is in crisis: human activities have resulted in consistent changes to ecosystems and to global and local patterns of biodiversity (Vitousek et al. 1997). Biodiversity is the variability among living organisms - animals, plants, their habitats and their genes - this includes diversity within species, between species, and of ecosystems. Scientists estimate that the current species extinction rate is between 1,000 and 10,000 times higher than it would naturally be (IUCN). This loss does not only concern emblematic or rare species, but also common species which provide a wide range of services critical to our survival: ecosystem services (Millennium Ecosystem Assessment, http://www.maweb.org/). An environmentally friendly railway must take into account into its maintenance this societal, politic and environmental problem.

Railways are in part responsible for biodiversity loss both at global (CO2 rejects) and local scales. Many studies showed in particular that transport networks are at the origin of habitat fragmentation and destruction, local pollutions, roadkills, noise effects, refuge and corridor areas for invasive alien plants (Forman & Alexander 1998; Trombulak & Frissell 2000; Seiler 2001; Hansen & Clevenger 2005; Coffin 2007).

On the other hand railway edges represent important green areas; their surface, adjacent to 29,915 km of exploited ways, is estimated to 49,000 ha in France (source: SNCF-RFF). Railways are linear elements crossing lots of different landscapes and connecting cities between them. Consequently their vegetated edges may play a positive role as refuge and corridor for native flora and fauna, especially in human-dominated landscapes (e.g. urban or intensive agricultural areas), where linear patches of habitat and green areas are scarce (Tikka, Hogmander & Koski 2001; Hansen & Clevenger 2005; Le Viol et al. 2008).

Vegetation management, which represents an important topic in railway networks maintenance, is a considerable source of expending for railway companies. However this management is necessary for security matters, to prevent many risks as fires, lack of visibility for train drivers, fall of trees on the catenaries, fall of leaves on the tracks that may result in train spin. In another hand a well-considered management of these areas, taking into account environmental matters, may be an opportunity for biodiversity conservation; however this conception has to be economically bearable. Is it possible to improve the cost efficiency of vegetation management and maintain biodiversity in railway edges?

Road and highway network managers have already started to consider this question since many years as scientists found possible contribution of road edges to the conservation (Way 1977) of indigenous flora (Spooner et al. 2004; O'Farrell & Milton 2006) and fauna (Meunier et al. 1998; Ries, Debinski & Wieland 2001) and gave some management solutions (Parr & Way 1988; Tikka et al. 2000). Railway networks have been less considered in literature, even if they might have fewer negative impacts on biodiversity than roads as there is no salting, paved surfaces are less important,

2 Challenge G: An even more competitive and cost efficient railway trains circulation is not as important as in main roads or highways and vegetation management is likely less intensive.

Biodiversity is extremely complex, dynamic and varied and indicators are a way of presenting and managing this complex information in a simple and clear manner. Numerous indicators have been developed to monitor environmental and sustainable development issues but less are recommended specifically for measuring biodiversity (see http://www.iisd.org/measure/compendium/), no one exists in the railway context. Therefore there is a need of indicators to monitor biodiversity in railway edges after vegetation management.

The aim of our research was then to: (1) understand the ecological role of railway edges (habitat, refuge, corridor, barrier) (2) search for biodiversity respectful and economic management solutions (3) develop scientific biodiversity indicators for railway systems by selecting target species

3 Challenge G: An even more competitive and cost efficient railway

Methods

Flora and fauna inventories Since we wanted to assess the ecological role of railway edges, we chose different taxonomic groups. Firstly plants which are at the target species for management. Grassland vegetation dominance is recommended in railways edges, especially near the tracks, in order to prevent security problems. Note also that grassland is a habitat which is in regression in Europe since the decrease of extensive agriculture. We thus chose to work mostly on this kind of vegetation. As railways have been considered an important source for plant invasions (Ernst 1998; Hansen & Clevenger 2005) we also choose to focus on an invasive species: Senecio inaequidens. This species was introduced from South Africa in Europe at the end of the 19th century and beginning of the 20th century through wool transports (Lachmuth, Durka & Schurr 2010). Some scientists argue that this plant have expanded and still expand today through road and railways (Ernst 1998). Since it contains alkaloids which are toxic to livestock and humans, S. inaequidens may cause economic and ecologic problems if it establishes and becomes abundant in natural or farmed grassland ecosystems (Scherber, Crawley & Porembski 2003). Therefore we checked if this species expanded across railway edges and for that purpose we used genetic tools. Secondly we studied snails, which have poor powers of dispersal and are potentially important for decomposition and as food for birds (Gotmark, von Proschwitz & Franc 2008). Lastly, we worked on Orthoptera which is an order of insects including the grasshoppers, crickets and locusts which are important components of grassland ecosystems and prey sources for many predators such as birds or spiders (Marini et al. 2008). We limited our study to the Parisian region (Ile-de-France), where the railway network is the most developed in France. We chose to work on normal railway lines (other than TGV: high-speed trains) as they represent the major part of the French network.

Study sites and lines The study on plants and snails was conducted in 2009 along two long-established railway lines (built in 1840 and 1847) in the south of the Parisian region (see figure 1). This region is densely inhabited with 20% of the national population living in just 2% of the nation’s land area. The two lines cross many cities and towns from the south of the region towards the center of Paris, thus they traverse a landscape structured by different degrees of urbanization. The vegetation found along the borders of train tracks is spontaneous (not sown) and mainly interrupted by railway stations, and overpasses. We wanted to minimize variations in environmental variables that we did not want to test, thus we tried to standardize sites using aerial photographs and field surveys. We selected all sites with the following characteristics: (1) bordered by the same environment: on one side the ballast and rails and on the other side, a small paved road (or a parking lot) and dwellings; (2) exhibited the same features: grassland vegetation less than 1 m in height, similar border width and slope. We identified 71 study sites along the two lines responding to these criteria, located between 70 and 4 km from the center of

4 Challenge G: An even more competitive and cost efficient railway

Paris. Each site was also characterized by its management practices: herbicides, mowing or none. We had threes years of sites management history. In order to check for a potential effect of local variables we measured edges width, slope and soil characteristics.

Within the center of each site, we established a 50 m-long transect 4 m from the rails and inventoried all vascular plants in five sample quadrats (1 m²) distributed every 10 m.

At the same place, we placed three woody planks and three construction bricks which materials retain moisture and are attractive for snails during dry periods. After one year we sampled all snails that were present under both the planks and the bricks. All samplings were done in the same meteorological conditions.

For the study of the invasive species Senecio inaequidens, we worked on three radial railway lines (one was common with the previous study), starting from Paris and directed to the north, the south and the east of the region. In 2010 we collected the leaves of 30 individuals of S. inaequidens (which represent a population) in railway stations approximately every 5 km starting from three different railway stations in the center of Paris. A total of 740 individuals were collected. We made genetics analyses using microsatellite DNA markers and investigated the genetic population structure.

In 2010 we inventoried Orthoptera in five different radial lines (up to 200 km). One of them was common with plant inventories. Many of these insects produce ultrasonic mating calls (above the range of human hearing) produced by stridulation. We thus conducted acoustic surveys with an acoustic recording device (frequency-division bat detector). This allowed also having information on bats. The records were made from running trains in crepuscular period. All individuals were precisely located on maps using a GIS.

Data analyses To assess for the ecological role of railway edges we compared all the data we collected to data on flora and fauna from the French National Museum of Natural History with statistical methods. For that purpose we used different biodiversity metrics as species richness, i.e. number of species, and diversity which is an index that incorporates richness and abundance of species. We also defined all species by their life history characteristics, or species traits, which reflects their characteristics (size, weigh, etc.) and their “way of life” including growth, feeding, movement, dispersion, and reproduction. The use of these tools allows making a finer analysis of species behaviour, including for plants. For plants, many databases giving these species traits are available (Klotz, Kühn & Durka 2002).

For each taxonomic group we assessed which factors at different scales were influent on species distributions along railway edges: (1) landscape and particularly urbanization, (2) management and (3) local factors.

5 Challenge G: An even more competitive and cost efficient railway

To assess the role of landscape we calculated the areas of the main land cover types in the surrounding landscape of each site and line using GIS tools. Then we tested if landscape had a significant effect on plant richness, diversity or species traits and compared our results to literature on other kind of habitats, for example isolated patches of forest or parks in urban areas. Concerning plant and snails, we surveyed sites with different management practices; we thus tested the effects of these practices on species richness, diversity and plant traits. Local factors as type of soil, surrounding slope, edges width were also included in our analyses. We used either the presence or the absence of edges breaks (stations or overpasses) to test the corridor role of railway edges for plants. Our hypothesis (H) was that if railway edges are corridors, two plant communities which are spatially connected (i.e. edge is continuous) should be more similar than two communities that are not connected (i.e. edge is interrupted by a station or an overpass). We tested it both for the whole plant community and for species traits.

Figure 1: Map of study railways and sites for each taxonomic group

6 Challenge G: An even more competitive and cost efficient railway

Results and discussion

Flora In the 71 study sites (355 m²) we observed a total of 186 plant species and within a site (5 m²), the number of species ranged from 6 to 32 (18.9±5.9). This represents 11% of the regional flora; however, we remember that our inventories were not representative of the whole richness of railway edges as they were limited in space and time. 82% (n=153) of the species we found were indigenous from France and 5% (n=10) of them were invasive species. We also found some rare species as for example Himantoglossum hircinum which is an orchid. According to urbanity classification by Klotz & al (2002) which reflects the affinity of plant species towards urban areas, 39% of species that we found were urbanophobes (rarely in cities), 45% urbanoneutral and 16% urbanophiles (mainly in cities). Therefore, in urban areas railway edges are mostly a habitat for common species and surprisingly they are not mostly urbanophile species, as we could imagine. The mean urbanity of our more urbanized study sites was similar to the mean urbanity of wastelands that have been show to work as refuge for flora in urban areas (Muratet et al. 2007). Therefore, we can hypothesize that edges are a refuge for flora and in particular for urbanophobe species in urban areas. However railway host almost all invasive species that are present in the study region, so they are a habitat for these species that are considered as problematic for biodiversity conservation and that are an important source of expending for nature managers (Gordon 1998; Olson & Lars 2006). These species are also problematic and thus are specific targets for railway vegetation managers as they grow and reproduce very fast. So concerning invasive species railway maintenance goes in the same direction than biodiversity preservation.

Landscape effect Concerning the effects of the landscape on species communities we found that, contrary to what other authors found in isolated patches of habitat, the surrounding urbanization did not have any effect on plant richness, diversity and most of plant traits. However we found an effect of urbanization on plant traits that are related to abiotic conditions as temperature, soil nutrients and moisture. These results shows that railway edges plant communities are sensitive to the landscape effect but they do not operate as isolated patches (e.g. urban parks or woods). This might be a signal for a corridor effect: the connection between communities would allow mitigating the effects of urbanization. However as we found an effect of urbanization on invasive and exotic species this would mean that urban areas are important sources for these species and there is no evidence for a corridor role of railways concerning these species. This will be more precisely assessed by our study on S. inaequidens which is still in progress.

Corridor role and railway structures interrupting biological fluxes Regarding the corridor role of railway edges - tested through the presence of a railway edge break (overpass, station) - we found that the presence of a break resulted in more dissimilar communities than connected communities. According to our hypothesis (H), this highlights a potential

7 Challenge G: An even more competitive and cost efficient railway corridor role of railway edges. However, this role is not homogenous among species: edges did not seem to be corridors for poorly mobile species (e.g. with gravity dispersed seeds). In contrast edges might be corridors for highly mobile species (e.g. pollinated by the wind) and for moderately mobile species (e.g. pollinated by insects or with wind-dispersed seed – seeds are heavier than pollen) but the latter are interrupted by railway breaks. We found that stations, contrary to overpasses did not seem to be interruptions for most of the species. An explanation may be that train blasts, which likely carry wind-dispersed seeds may be interrupted by the air turbulence when the train pass overpasses (as shown by Ernst (1998) for achenes). Cars are well known to be responsible of seed transportation (Zwaenepoel, Roovers & Hermy 2006). This air flow may also be interrupted when trains slow down or stop in stations. In stations seeds may then be picked up again by air turbulence or wind. On the contrary seeds likely fall from the overpasses as these have often very narrow paved edges. Similarly plants that have seeds transported by small animals (pollinators, ground insects or small mammals) may also be disturbed by paved surfaces and presence of humans (stations).

Management Surprisingly we did not find strong effects of management on plant communities. This was probably due to a high heterogeneity of management practices that did not permit to have many replicates, even with 71 study sites. However, sites that received mechanical management had slightly a smaller number of invasive species. Herbicides are known to make native plants rare, this make invaders become more abundant in response to decrease in native species (Rinella et al. 2009). Furthermore, herbicides are known to be noxious for terrestrial and aquatic ecosystems. For example, glyphosate that is a very common herbicide molecule widely applied to railway edges, has been show to be lethal to terrestrial and aquatic amphibians, insects and birds (Freemark & Boutin 1995; Relyea 2005). Therefore, mechanical solutions, even if more expansive, are a more respectful for biodiversity. More generally, long-term strategic plans incorporating economical, sustainable and multi-year integrated approaches for vegetation management enhance the utility of ecosystems and prevent plant invasions, as showed by DiTomaso (2000) in rangelands. The future analyses on fauna will help to understand which are the best solutions for economic and biodiversity respectful vegetation management practices.

Fauna We found 11 species of Orthoptera along the five railway lines, four of them were very abundant (Tettigonia viridissima, Leptophyes punctatissima, Ruspolia nitidula, Phaneroptera nana) and the others were rarer (Pholidoptera griseoaptera, Conocephalus dorsalis, Phaneroptera falcata, Pholidoptera femorata, Platycleis tesselata, Platycleis albopunctata, Conocephalus fuscus). All the species are very common species in the area and belong to the same family and order. This is very poor, for example Kutschbach-Brohl et al. (2010) found up to 17 families in airport semi-natural grassland. However our protocol did not allow having an exhaustive inventory of all species as it was done in a precise period of the day and only for stridulating species. We counted about 2000

8 Challenge G: An even more competitive and cost efficient railway individuals along the five sampled lines. The interest of our protocol is thus to compare the presence and abundance of species along habitat gradients and for different management practices. For each species we have inventories (from National Museum of Natural History) in road verges, thus we will be able to assess if Orthoptera penetrate more into urban areas through railways or through roads, this should inform us on the refuge and corridor role of railway edges.

Snails should give us information about the barrier role of railways for poorly mobile species. Does the snail communities which live in edges on either side of railways are similar? In that case we should suppose that snails may cross the train platform, which would not be a barrier for these species, the analyses are still in process. As snails are key organisms in the food chain (consumers) the richness and diversity of their communities may be an indicator of the ecosystem health and may give more information concerning management practices.

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Conclusions

This study has not reached its end yet, but until now we found that railway edges may have an interest for biodiversity conservation in that they may play a positive role as habitat, refuge and corridor for different taxonomic groups. These roles may exist also without a specific management. The challenge for railway vegetation managers, as it is for railway planners, is to better integrate this topic into their decisions and to try to mitigate the negative impacts of railways that still exists as pollutions due to herbicides or refuge for alien plants.

Concerning management, mechanical techniques are known to be more respectful for biodiversity than the use of herbicides. In order to reduce the costs of management it is important to work on multi-year integrated approaches which should be beneficial also for biodiversity.

Many countries are trying to create green networks to link natural areas (Jongman, Kulvik & Kristiansen 2004; Zhang & Wang 2006), according to our results on plant communities, railway edges may be included in these networks in urban contexts. However it would be possible to improve railway connectivity for organisms. We found that overpasses likely interrupt some biological fluxes (for plant species); therefore we suppose that an action on them as for example the enlargement of overpass width or the installation of vertical structures on it during railway construction or renovation could yield a good seed retention system. However these different solutions need to be tested.

The method we used for sampling Orthoptera is very interesting because it consents to have information on species presence, abundance and variations on the whole railway network. Orthoptera recordings do not require much time and scientists are working to create softwares for automatic identification of species in order to make easier and faster the species inventories. Furthermore, the cost of this kind of inventories may become quite low. If our results will show that Orthoptera are good biodiversity indicators for railway edges, it would be possible to locate on maps the “hotspots of railway biodiversity” quite easily.

The world’s urban population is expected to grow by 84% by 2050 (UNDESA 2010) and consequently, urban landscapes will also expand all over the planet. Urbanization is considered to be one of the most severe, large-scale perturbations affecting biotic communities (Czech & Krausman 1997; Vitousek et al. 1997). In such contexts, large spaces as railway edges - with a well-reasoned management - may be an interesting solution for biodiversity and ecosystem services conservation, which is an increasing social and politic demand.

10 Challenge G: An even more competitive and cost efficient railway

Additional information This work is part of a PhD thesis started in January 2009. It is co-funded by SNCF Infrastructure branch (INFRA/CSC ER IM 1) and ANRT (Agence Nationale pour la Recherche Technique). Logistic support is provided by SNCF Environment department of the Engineering branch (INFRA/IG-LG-ENV). MNHN (French National Museum of Natural History), UMR 724 CERSP is partner for scientific supervision.

References

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