Autumn will be delayed by up to two months in cities due to the impact of LED streetlights on certain tree species. This scenario emerges from a pioneering study by the University of Pisa on the effects of LED urban lighting technology published in the journal Science of the Total Environment. The research has examined two species that are widely used in urban environments, namely the London plane (Platanus × acerifolia) and the large-leaved linden (Tilia platyphyllos), to assess the consequences on the physiological and biochemical processes of the two species.
The results showed a delay of about two months in the onset of winter dormancy, i.e. the resting period that allows the plants to get through winter ‘in a sleeping condition’, but only for plane trees, which are in fact more sensitive to night lighting than linden trees.
“Street lighting disturbs the natural physiological processes and circadian rhythms of all living organisms, including the ‘green citizens’ that populate our streets,” explain Dr Marco Landi, researcher at the University of Pisa, and Dr Ermes Lo Piccolo, researcher at the University of Florence.
The experiment conducted at the Department of Agricultural, Food and Agri-Environmental Sciences by researchers Lucia Guidi, Marco Landi, Giulia Lauria, Ermes Lo Piccolo, Rossano Massai and Damiano Remorini involved 15 specimens of each species, 5 of which constituted the control group while 10 were illuminated with LEDs at about 2 metres from the ground (30 cm from the crown). The observation thus involved the leaves in three phenological stages (young, mature, senescent).
On a physiological level it was found that mature tree leaves in both species have a lower rate of CO2 assimilation at dawn. According to the researchers, this is a kind of temporary ‘hangover effect’, as the plant has photosynthesised during night hours because of lighting.
There are currently around 326 million streetlights in the world, and the number will rise to 361 million by 2029, which is a major problem for energy consumption. While a solution may be the use of LED streetlights, it is necessary to understand their effects on trees, as this technology has a different light spectrum, peaking in the blue and red regions, from, for example, the old street lamps, which peak in the yellow-red region.
“Our study,” concludes Prof. Remorini, “represents a first step in this direction, the aim being to provide useful indications in terms of sustainability and of the livableness of our cities for all living organisms.”