Ecological impacts of nocturnal artificial lighting along the linear transport infrastructures and their dependencies. Influence of LED light parameters on the movements of bats
The extension of urban areas and linear transportation infrastructure (LTI), whether road, rail or river, has resulted in different types of impacts on biodiversity (direct and indirect habitat loss, barrier effects, pollution, collisions). At the same time, their green dependencies have emerged as habitats and corridors for certain species, contributing to maintaining a certain biodiversity in highly anthropized landscapes. One of the current challenges is thus to reduce these impacts by promoting connectivity and limiting associated pollution (light, chemical, noise). As a result of artificial night lighting, much of which is installed along interurban (e.g. freeways, national highways), urban (e.g. boulevards, avenues, bypasses) and rural (e.g. access roads, traffic circles, main streets) roads, light pollution is increasing worldwide by 6% per year and currently affects more than 88% of Europe's land surface. Artificial night lighting has thus become one of the threats to biodiversity conservation, impacting the spatio-temporal dynamics of species by 1) disrupting their circadian and seasonal rhythms, and 2) generating a loss and fragmentation of nocturnal landscapes. It is therefore crucial that it be taken into account in the management strategies for LTBIs. Different strategies to limit these effects exist such as the reduction of intensity, duration of lighting, choice of blue and UV wavelengths. However, there is a lack of knowledge on the relative effectiveness of these measures and studies (mostly on bats) mainly consider their effects on the abundance-activity of individuals but little on behaviour, which limits the understanding of the mechanisms involved.
The CHIROLUM project thus aimed to improve this knowledge by focusing on the impacts of these parameters on chiropterans, the challenge being to identify ways to reduce the ecological impacts of lighting (especially LEDs) along the ILTe while reconciling the social and regulatory issues. Set up in partnership between 6 research teams at the interface between ecology, physics and geography of the environment, the CHIROLUM project was based on two in situ ecological experiments (Toulouse and the Netherlands) and surveys of stakeholders and users (Toulouse).
If certain characteristics of artificial lighting can mitigate certain ecological impacts, the project emphasizes that the most effective solution to reduce them remains their removal and extinction. Indeed, the presence of artificial lighting affects all groups of bats regardless of the parameters tested. Changing the lighting color to warmer colors (such as red with a minute amount of ultraviolet and blue light) does not seem to be as effective in terms of reducing functional (barrier effects) and behavioural disturbances of bats (escape to sub-optimal crowded habitats) as recent studies have suggested. These "local" impacts seem, however, to be limited to the "action" range of light, within a radius of a few dozen metres. Thus the reduction of the intensity and range (directionality) of the lighting could be a lever for reducing impacts. Thus an orientation of the lighting avoiding ecological corridors (such as the riparian zones of canals and bridges) could limit the impacts on their functionality.
The ecological disruptions generated by this light pollution and identified within the city of Toulouse could be greatly reduced through an adapted management of the lighting stock integrating extinction and reduction schemes. This management would be all the more effective as it would be facilitated by communication between the institutional services (currently siloed) concerned by these issues of biodiversity and artificial lighting. This communication would probably be a force to overcome the shortcomings observed in terms of law enforcement (Batho decree, 2013) and could create favourable conditions to recreate, promote and maintain the functionality of the main green corridor crossing the urban area (Canal du Midi). Beyond Toulouse, this concerted management of lighting, integrating its impacts on biodiversity, would make it possible to better integrate these ILTEs into the ecological continuity networks.