So, in their different ways, plants and animals react and are controlled by their circadian rhythms. Unfortunately research evidence shows that by extending daylight hours artificial light is disrupting these natural patterns, with adverse consequences. I’m very lucky, living in the country where the only light I see is occasional car headlights and and twinkling plane lights passing among the stars. But many people feel imprisoned by the urban light shield and long to see Venus and the moon.
And though we can escape the city’s gloomy orange pall by driving, cycling or walking out of town, animals and plants simply can’t.
A citizen science study by the British Trust for Ornithology [BTO] in 2014 investigated the effect of light pollution on bird behaviour in winter. Researchers asked Trust members from throughout the UK to record when, in January, birds first arrived at feeders. They combined this information with the strength and duration of artificial lights, temperature and rainfall. The results astonished them.
The 10 most frequently recorded species arrived at the feeders no earlier in areas with high artificial light levels. The birds were not taking advantage of what we might think of as extra time to forage. Much research has been conducted on how artificial light in built up areas changes the timing of birds’ breeding behaviours so it is puzzling as to why birds seem not to be taking advantage of the extra hours of light to forage more in winter.
The circadian rhythm affects plants as well as birds: they too need specific day/night patterns to function properly, determining periods of action and ‘sleep’. They use photoreceptors to determine day length, triggering major events like bud burst and leaf drop and all the processes linked to them.
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In autumn and early winter deciduous plants are programmed to prepare for winter by dropping leaves and, in some cases, dying back for winter dormancy. Artificial light interferes with this, effectively extending the number of ‘working days’ for perennials. We’ve all seen plants coming into leaf much earlier than usual, and it has been shown that artificial light is an important component of this. So plants can become stressed by starting the season on average seven days early and finishing later.
Over the festive period many of us bring a bit of sparkle to the garden and contribute a little artificial light but we can minimise this.
Strings of lights along the side of a building, fence or Christmas tree do cheer things up. We go mad here and cut down a seven or eight-year-old Norway Spruce tree and adorn it with a few packs of lights. There are endless gadgets available. Since the local fox or badger doesn’t participate in the festive fun, it won’t enjoy ours, so the lighting should be on a timer to come on between sunset and bed time. I turn mine off after putting the ducks to bed.
It’s even better to use low voltage bulbs and battery or rechargeable lights as they’re less bright. ‘Warm white’ are said to be less disruptive than blue spectrum LEDs.
Plant of the week
Scots Pine, Pinus sylvestris, is at its best in winter: whether daubed with snow or outlined against an early morning sky and the warm, red brown bark glows when the low winter sun shines on it.
Mature trees need space and are not suitable for smaller gardens but, if you can, grow a Scots Pine and share its beauty with your neighbours.
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