Experimental illumination of a terrestrial ecosystem: Effects at the population and individual level

Background/Question/Methods

Nocturnal illumination leads to a permanent disturbance of natural habitats and there is accumulating evidence for – often negative – impact of artificial light in an increasing number of species. However, most of these studies are correlative and only include immediate or short-term effects of artificial light at the level of the individual while long-term consequences are still largely unknown. The current, worldwide change to LED outdoor lighting allows for custom-built spectra which can therefore be designed to minimize the negative impacts on flora and fauna. In order to experimentally assess short-term and long-term effects of artificial light with different spectra on the presence and the population density of species we have set up a large-scale monitoring experiment. We have put up 120 light posts at forest edges to illuminate natural habitats from sunset to sunrise with three different spectra: white light, and light with either reduced short or long wavelengths. The effect of the light is monitored for three years following a control year without light (2011); data are compared with control sites (dark) present throughout the experiment. Breeding birds, bats, other mammals, moths and vegetation are carefully monitored by specialized field biologists according to rigid protocols. In parallel, we experimentally test for effects of artificial light on the life history of birds and insects (moths) in separate in-depth studies. Changes in daily and seasonal timing, such as changes in onset of dawn chorus and laying date in birds are studied, and the effect of light on the herbivory and development of moth caterpillars.

Results/Conclusions

Artificial illumination of nest boxes with breeding great tits (Parus major) induces strong changes in chick provisioning behavior, which may be related to interference of nocturnal light with the assessment of time of year. The development of moth caterpillars (Mamestra brassicae) is profoundly affected by illumination at night. Our unprecedented monitoring experiment will provide key insights in how nocturnal illumination affects flora and fauna and how light spectra can be designed to minimize the negative effects.