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Earlier lilac blooms spur local climate change research

UToledo: Common lilac blooming one day earlier every 3 years since 1970s
Published: Apr. 29, 2021 at 9:49 PM EDT
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TOLEDO, Ohio (WTVG) - Stephanie Nummer has taken an unconventional approach to climate change data. The University of Toledo Ph.D student looked at the long-term trends of lilac blooms in North America, and found a trend about a half-century in the making.

“Lilacs are blooming earlier by about a third of a day per year”, she explains. “Year to year, it isn’t a whole lot, but if you think about it over 30 years, that’s 10 days earlier.”

Nummer’s paper, published in November, found May 15th to be the common average date for lilac blooms in North America in the early 1970s, which has now shifted up near the start of the month. She used over 50 locations in the U.S. and Canada to gain a clearer picture, and to make sure it wasn’t just a trend in the Buckeye State. (For reference, Wooster, Ohio -- our closest such station -- averaged May 6th as their bloom start date back in 1974.) Nummer also discovered signs of a shift as far back as the mid-1960s in places like California.

“One really cool thing about lilacs is that because they’re so well-known, people have been recording data on them for a while... because we have that information, we can see long-term trends, and how these flowers are responding to climate change,” says Nummer. “There are locations that have recorded data of when these lilacs first bloomed, year after year after year... so we used locations that have at least 30 years worth of data.”

Even excluding our own very early bloom this year -- Wooster’s was marked as March 13th -- the lilac finding is twice the estimated rate from a similar study on DC cherry blossoms. As Nummer explains it: “They’re going to react a bit differently, but one cool thing about the model we developed is that it can be applied to multiple species in one location as well.”

Of course, any bloom or blossom needs a couple of key ingredients. “The main two components that go into a flower blooming are sunlight and temperature,” she reminds us. “As temperatures warm earlier and earlier in the year, sunlight will start playing a bigger role in that.”

One consequence of that early bloom involves “trophic mismatch”, where some levels of the food chain may peak at different times. Lilac can attract and shelter some migratory birds, for example: “When they stop over, especially in Ohio during Biggest Week... is their food peaking then, or is it peaking earlier, and how do birds react to that?”

There are still many connections to make and verify, though Nummer hopes her research can be built upon with future studies.

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