Ecologists have reviewed archive footage of the Tour of Flanders cycling race going back three decades to reveal the effects of climate change on trees.
The Tour takes place on a 267-kilometre route along Belgian roads in early April every year. While he was watching historical clips of the race online, it occurred to Pieter De Frenne from Ghent University, Belgium, that the footage might provide a valuable record of how the timing of leafing and flowering has changed.
鈥淚 noticed that that these past editions are often in very cold weather, and the trees in the landscape never have leaves,鈥� he says.
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So in collaboration with the Belgian broadcaster VRT, De Frenne and his team spent several weeks watching archive footage and gathering data on the trees. 鈥淚t was great fun,鈥� he says.
The data confirmed his suspicions. Before 1990, hardly any trees had grown leaves by the time the Tour took place. After that, more and more trees in the TV footage were already in full leaf, including magnolia, hawthorn, hornbeam and birch trees.
鈥淚t was very remarkable. The differences we observed were more than we expected,鈥� says De Frenne.
This shift coincided with a rise in the average temperatures in the region, by about 1.5掳C since 1980.
Earlier leafing allows trees to grow faster, but this has knock-on effects for other species, says De Frenne. For example, flowers growing beneath the trees may not get enough sunlight to bloom, and this means less nectar is available for insects.
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Methods in Ecology and Evolution
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