Nearly four decades of cycling race video reveals climate change’s effects


  • A team of ecologists has used video from key locations along the route of the annual Tour of Flanders cycling race to understand how plants are responding to regional rises in temperature.
  • After watching more than 200 hours of footage from 36 years of the race, the team found that trees began producing flowers and sprouting leaves earlier in the season.
  • By 2016, trees were 67 percent more likely to have produced leaves by the time of the race than in the 1980s. By comparison, few if any trees had leaves before 1990.
  • The researchers believe that analyses of video from other cycling races and similar annual events could yield new insights into the ecological changes that temperature changes instigate.

Scientists in Belgium have used 36 years of footage from an annual bicycle race to pinpoint the time each year when leaves and flowers appeared on trees and shrubs, allowing them to chart the effects of climate change.

The data they collected could also help researchers forecast shifts in these patterns if temperatures continue to rise.

“Only by compiling data from the past will we be able to predict the future effects of climate change on species and ecosystems,” Pieter De Frenne, an ecologist at Ghent University in Belgium and the lead author of the study, said in a statement. De Frenne and his colleagues reported their findings July 3 in the journal Methods in Ecology and Evolution.

The researchers counted the leaves and flowers that appeared on individual trees, such as the pear tree in the background of this picture, located at key points along the course. Image © Flanders Classics.

The Tour of Flanders is a famous one-day cycling race, attracting elite riders from around the world to northern Belgium, typically in early April. Average temperatures in the region have risen by about 1.5 degrees Celsius (2.7 degrees Fahrenheit) since 1980. Because the race takes place in the spring every year and covers a similar route each time, De Frenne and his colleagues suspected that video from key locations could help them understand how plants responded to that temperature rise.

They began by pulling together footage from the Flemish television station VRT taken during the race between 1981 and 2016. They then analyzed some 200 hours of it, looking at 46 individual trees and shrubs and calculating a rough estimate of how many leaves and flowers they had at each point in time.

As temperatures rose, trees began producing flowers and sprouting leaves — what ecologists call “flushing” — earlier in the season. In 2006, an individual tree or shrub was almost 20 percent more likely to have flushed during the Tour of Flanders than in the 1980s. That figure rose to 67 percent in 2016. By comparison, few if any trees had leaves before 1990.

The ecologists viewed more than 200 hours of film covering 36 years of the Tour of Flanders. Image © Flanders Classics.

That increase in leaf cover probably represents a mixed bag of knock-on effects, De Frenne said.

“Early-leafing trees can be good news for some species as they grow faster and produce more wood,” he said. “However, their leaves also cast shadows. When trees flush earlier in the year, they shadow for a longer period of time, affecting other animals and plants, and even whole ecosystems.”

The impacts could then ripple through the local ecosystem, De Frenne added.

“Some of the flowers growing under these trees may not be able to receive enough sunlight to bloom,” he said. “As a result, insects can go without nectar and may struggle to find enough spots to sunbathe.”

Similar analyses of other cycling races, along with other events such as concerts and golf tournaments, could enhance scientists’ understanding of the effects of temperature change, the researchers said. Image © Flanders Classics.

The team believes that similar analyses of other cycling races, along with running races, concerts and golf tournaments, could yield new insights into the ecological changes that temperature changes instigate, De Frenne said.

He added, “Our method could also be used to collect data on other aspects important for ecological or evolutionary research, such as tree health, water levels in rivers and lakes, and the spread of invasive species.”

Banner image of a screenshot of archived footage from the Tour of Flanders © Flanders Classics.


De Frenne, P., Van Lagenhove, L., Van Driessche, A., Bertrand, C., Verheyen, K., & Vangansbeke, P. (2018). Using archived television video footage to quantify phenology responses to climate change. Methods in Ecology and Evolution.

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