Climate cues and tree genes best predictor of leaf burst in spring

Thousands of people await the blooming of cherry trees as a welcome sign of spring every year. Now, thanks to new work by researchers at UBC and Université de Montréal, it may soon be possible to predict more precisely when the first tiny buds will burst forth.

Elizabeth Wolkovich, a forest and conservation sciences professor at UBC, and Simon Joly, a biology professor at Université de Montréal, found that warming temperatures had the strongest influence of the timing of budburst—regardless of the specific species of tree or shrub.

“It’s well-known that budburst is affected by how much time plants have spent in cold and warm temperatures and by the amount of daylight they receive, or daylength,” said Wolkovich, an ecologist who previously taught at Harvard University. “However, this is the first study that compares the strength of these factors relative to each other, within and across different species of plants growing hundreds of miles apart. As climate change continues to reshape our winter and spring temperatures, understanding how all these factors work together to cause budburst each spring will become more critical to managing our forests and parks.”

The researchers collected branches from 10 different tree and shrub species found in both Quebec and Massachusetts—striped maple, American beech, northern red oak and a few types of honeysuckle, poplar and blueberry. The samples were obtained in mid-winter, after the plants had experienced what researchers judged a sufficient number of cold days to allow budburst, given the right conditions.

The branches were then stored in special growth chambers at Harvard, where they were exposed to different combinations of temperatures and daylength (15 or 20 degrees Celsius, and eight or 12 hours of daylight) and monitored until their buds started to produce leaves.

Results showed that branches kept at warmer temperatures burst bud by 20 days earlier compared to branches that were kept in cooler temperatures. “This was true across the Quebec and Massachusetts sites, and on average across all species, although there were significant variations depending on species, with trees like the American beech responding more markedly to warmth and daylength,” said Wolkovich.

Daylength also influenced budburst to some degree—samples that received more daylight burst their leaves about 12 days earlier than specimens that received less—but warmth played a bigger role.

In addition, the researchers found that incorporating DNA information into the analysis enabled them to better predict the day of budburst for all the different species under study.

“We saw that related individuals, when subjected to the same climatic cues, burst bud at similar time. This information may eventually allow us to anticipate trees and plants’ reaction to environmental cues, depending on the behaviours of other members of the same species or genetically related species,” said Simon Joly, who is also a botanical researcher at the Jardin botanique de Montréal.

“These results also suggest that some individuals in tree and shrub species could be better adapted to future climate warming, for instance if they react better to changes in temperature,” Joly added. “This opens many research opportunities.”

For the next stage in this research, Wolkovich and her colleagues plan to study trees and plants in British Columbia to understand how different factors play out at different climate zones.

“We don’t have the complete picture yet—we still don’t know exactly how climate change will affect the timing of spring,” she said. “But this new information points the way forward. It confirms that warming does play a big role, and that genetics can inform adaptation strategies for plants as climate change continues to accelerate.”

The study, funded by William F. Milton Funds at Harvard University, was published today in Methods in Ecology and Evolution.