A plea for a worldwide development of dark infrastructure for biodiversity – Practical examples and ways to go forward

Artificial light at night (ALAN) has been massively deployed worldwide and has become a major environmental pressure for biodiversity, especially contributing to habitat loss and landscape fragmentation. To mitigate these latter, green and blue infrastructure policies have been developed throughout the world based on the concept of ecological networks, a set of suitable interconnected habitats. However, currently, these nature conservation policies hardly consider the adverse effects of ALAN. Here, we promote the integration of darkness quality within the 'green and blue infrastructure', to implement a ‘dark infrastructure’. Dark infrastructure should be identified, preserved and restored at different territorial levels to guarantee ecological continuities where the night and its rhythms are as natural as possible. For this purpose, we propose an operational 4-steps process that includes 1) Mapping of light pollution in all its forms and dimensions in relation to biodiversity, 2) Identifying the dark infrastructure starting or not from the already identified green/blue infrastructure, 3) Planning actions to preserve and restore the dark infrastructure by prioritizing lighting sobriety and not only energy saving, 4) Assessing the effectiveness of the dark infrastructure with appropriate indicators. Dark infrastructure projects have already been created (for example in France and Switzerland) and can serve as case studies for both urban and natural areas. The deployment of dark infrastructure raises many operational and methodological questions and stresses some knowledge gaps that still need to be addressed, such as the exhaustive mapping of light pollution and the characterization of sensitivity thresholds for model species.