[LUM#12] Flora on the Move

[LUM Magazine] - Published on June 2, 2020 in Science and Society

France’s flora is no longer what it was 10 years ago. Researchers have recently shown that the composition and abundance of plant species in France changed between 2009 and 2017. The cause? Global warming.

How are plants affected by global warming? While researchers have long shown that rising temperatures are altering the range of many animals, such as birds and fish, the consequences for plant life remained poorly understood… until now. A recent study examined changes in plant species between 2009 and 2017, and its findings are clear: France’s flora is changing.

Citizen science

“Compelling results: clear, precise, and robust,” notes Vincent Devictor. The researcher fromthe Institute of Evolutionary Sciences in Montpellier participated in this extensive study, which was carried out in large part thanks to the Vigie-Flore citizen science program. Amateur and professional botanists sample wild flora across France and share their observations with the National Museum of Natural History. This provides researchers with a wealth of valuable data. “In total, 320 volunteer observers monitored more than 3,000 sites each year for nine years using a standardized observation protocol, ” explains Vincent Devictor. As a result, 2,500 plant species were monitored in lowland areas across various environments—urban, agricultural, forested, or grassland—out of the 6,000 plant species found in metropolitan France.

To assess changes in the flora, the researchers took into account each plant’s temperature preference. “This is the optimal temperature required for their growth—their preferred temperature,” explains the researcher. They applied this metric to a dataset of 550 species representative of France’s common flora. “We then calculated the average preferred temperature of this collection and observed its evolution over time.” The researchers then realized that this average preferred temperature had increased between 2009 and 2017.

Preferred temperature

In practice? “This means that French vegetation is increasingly composed of species that tolerate high temperatures well, at the expense of species that prefer cooler climates.” Plants with a strong thermal preference are becoming more widespread and are colonizing new areas. This is particularly true of bearded oats and Madrid brome, which seem to be thriving under these conditions. Conversely, species with a low thermal preference have seen their abundance decline and have lost ground, such as false bindweed and wild chervil, which are disappearing from places where they were present just a short time ago. A real transformation of France’s flora in just 8 years.

Could such rapid change be caused by global warming? To investigate this, researchers analyzed temperature records from sites monitored by Vigie-Flore observers and found a significant increase in average temperatures between 2009 and 2017. “This increase appeared to be linked to the changes observed within plant communities, ” explains the ecologist. Indeed, sites with significant temperature variations are also those that have undergone substantial species replacement over time, with less heat-tolerant species giving way to more heat-tolerant ones.

Short-term

It’s a short step from there to saying that global warming is responsible for this change in the flora… “But before taking that step, we had to make sure that other factors—such as plants’ preference for nitrates or CO₂—weren’t responsible for this change,” adds Vincent Devictor. These parameters have not changed significantly over time at the monitored sites. “We can therefore clearly state that global warming is directly responsible for these shifts in wild flora. This is the first time that a response of flora to rising temperatures has been demonstrated on a national scale over such a short period, ” the ecologist emphasizes.

What are the consequences? “One might see this as good news, thinking that the flora is adapting quickly to rising temperatures, but it’s highly unlikely that this thermal adaptation will be perfect,” the researcher cautions. “There will be a delay that could affect all ecosystems, since plants are the foundation for the survival of all other groups, ” Vincent Devictor points out. Something to ponder during a future stroll through the garrigue… in northern France.

Keywords: Climate, Environment, LUM#12, LUM Magazine, Research, Company