Science - November 17, 2011

Green light for nature?

The Netherlands is among the most lit-up areas in the world. There is hardly a part of the country left where it is truly dark at night. Which is not a problem for human beings: we can close the curtains. But what does all that artificial light do to nature? Wageningen sheds light on the matter.

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Light attracts insects, that is one thing we know for sure. Everyone can picture a swarm of moths fluttering endlessly around a lamppost. Bats make the most of it. Where there is light, there is food. Artificial light provides a meal service. But beyond that, we are pretty much in the dark about its impact.
Moth numbers in the Netherlands have fallen by 30 percent since 1980. Is this because of artificial light? We don't know. ‘Little is known still about the ecological effects of light pollution', confirms Roy van Grunsven (Nature Management and Plant Ecology). Not that moths are on the brink of extinction. ‘But they are preyed on by other animals, and that does make the decline a problem'.
Van Grunsven and his colleague Kamiel Spoelstra (NIOO-KNAW) have already been working for a year on preparing the biggest ever study of light pollution in the Netherlands. Light on nature (www.lichtopnatuur.org) is the name of the study, financed by the technology foundation STW and involving ‘Wageningen' as well as a large number of nature organizations, estate managers, Philips and the Dutch oil and gas company NAM.

Oil rigs
It all began with the NAM in fact, explains Van Grunsven. Brightly lit oil rigs at sea disturb bird migration. So in 2005, the NAM introduced green lights specially developed by Philips, which attracted far fewer birds. That worked at sea, anyway. But what about flora and fauna on land? Is there such a thing as nature-friendly lighting, and if so, what does it look like?
To figure this out, the Wageningen researchers will study the effects of green, red and white light on nature for a period of three years. Nature will be in the limelight at eight locations, seven on the Veluwe and one in Drenthe. There will be four rows of five lampposts: one row each of red, green and white light, and one that remains unlit. It sounds easier than it is, explains Spoelstra. ‘The room for manoeuvre for this sort of experiment is very limited. Nature managers would rather not have any lampposts in their forests.'
Just getting access to the locations took the researchers six months. ‘We are pleased that we have now found eight places', says Spoelstra. So he gets to name names: the organizations voluntarily participating are Natuurmonumenten, Staatsbosbeheer, Drents Landschap, the ministry of Defence and Ede town council. The test sites themselves have already been monitored for a year for baseline data. They are all spots where forest gives way to open landscapes. A place where many species of birds, insects and small mammals congregate. And where it is fairly dark. The lampposts will be installed in the coming weeks.
Nocturnal life has been under scrutiny nearer home too. On the Bornsesteeg, a stone's throw from the campus, stands a battalion of eighty butterfly cages one cubic metre in size, covered in white gauze. It looks like a piece of modern art. But in these cages, ecologist Koert van Geffen is studying the impact of light pollution on vegetation. ‘It's about caterpillars' feeding', explains Van Geffen. ‘Butterflies don't really eat anything; they have very little impact on the vegetation. But what is the effect of artificial light on populations of moths? Do populations change in numbers and composition and how does that affect the vegetation?'
The installation at the Bornsesteeg is part of Light on Nature too. The test simulates the lighting situation along a typical country road in the Netherlands. Various species of grass and herbs grow in the cages, and each cage is lit individually, with the same red, green and white light used by Van Grunsven and Spoelstra.

Green light on cycle paths
Whereas Van Grunsven and Spoelstra look at the total ecological effect of artificial light, Van Geffen zooms in on moths. His moths cannot choose between light and dark, either. They cannot escape from the cage. One of the things Van Geffen wants to know is how the populations develop under the different kinds of light. There is no shortage of questions. ‘Caterpillars normally always eat in the dark, to avoid predators. Do they now eat less than they would in the dark? And what about reproduction? What happens to the excretion of pheromones under the influence of artificial light? And how do the males respond to that? According to Van Geffen, there are signs that males are more attracted to light than to pheromones. And that has consequences: without sex, no babies.
The knowledge gained could pave the way to more animal-friendly outdoor lighting. Green lights along cycle paths, for instance. Or red, for a particular species that is least bothered by red light. It is known that many insects and mammals are not very sensitive to red light. But green light may not be a magic bullet, warns Spoelstra. ‘Nowadays you often see councils putting in green lights because they are supposed to be good for nature. The harbour on the island of Ameland is lit in green and even the NIOO uses green outdoor lights. But this has still only been tested on oil rigs to attract fewer birds.'
 

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