Too much light at night forces trees to bud early

Light pollution triggers early spring study finds

Spring is coming more than a week early in those areas of the UK with the highest levels of night-time artificial light exposure, a study has found.

Research by a team from the University of Exeter and independent environmental consultants Spalding Associates has combined air pollution data from satellite images with information from the public about budding trees. The comparison revealed that in areas with the highest levels of night-time light exposure, citizen scientists reported spotting emerging leaves on trees up to 7.5 days earlier.

The team focused on larger trees such as oak, ash, beech and sycamore. However, they stressed the effects would most likely be seen across the fauna and flora of affected areas.

"Our finding that the timing of bud burst of woodland tree species may be affected by light pollution suggests that smaller plants growing below the height of street lights are even more likely to be affected," said Professor Richard Ffrench-Constant of the University of Exeter’s department of Biosciences.

The researchers filtered out effects of higher temperatures by focusing on non-urban areas. It is believed that the heat accumulated by larger cities can also cause plants to wake up earlier after winter.

The study analysed data from the past 13 years. The citizen data was taken from the Woodland Trust’s Nature’s Calendar in which members of the public record signs of the changing seasons.

"Analysis of Nature's Calendar data suggests that increased urbanisation is continuing to put pressure on the natural world, in ways that we could not have foreseen,” said Kate Lewthwaite, Woodland Trust citizen science manager.

"As the seasons become less and less predictable, our native wildlife may struggle to keep up with fluctuations that affect habitats and food sources.”

In the paper published in the latest issue of the journal 'Proceedings of the Royal Society B', the team described that early budding of oaks would, for example, affect populations of winter moths that feed on fresh oak leaves, which in turn could impact bird populations feeding on the moths. The study also found that later budding trees tend to be more affected.

"Such results highlight the need to carry out experimental investigation into the impact of artificial night-time lighting on phenology and species interactions," said behavioural ecologist Peter McGregor, of the Centre for Applied Zoology at Cornwall College Newquay.

The researchers hope the results will help start a discussion with local councils about more nature-friendly approaches to street lighting. The team plans to conduct further studies that would determine how the effects differ based on various wavelengths and types of lighting.

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