Flowers Are Blooming Earlier And Earlier Every Year, New Research Using The Meticulous Records Of Thoreau Show

As many people have already noticed, flower seem to be blooming earlier and earlier every year, coinciding with the rather mild winters that seem to be the new norm in many part of the world. And now new research has shown that the trend dates all the way back to at least the days of Henry David Thoreau and Aldo Leopold.


By using the “meticulous phenological records” that these two famous American naturalists left behind, researchers have been able to demonstrate that native plants throughout the eastern states “are flowering as much as a month earlier in response to a warming climate.”

This new research is important because it allows a deeper look into “the black box of ecological change”. It will also be very helpful for predicting the likely effects that a warming climate will have on many very important agricultural crops. Many of these crops are dependent upon flowering in order to produce the food that they provide.

“Compared to the timing of spring flowering in Thoreau’s day, native plants such as serviceberry and nodding trillium are blooming 11 days earlier, on average, in the area around Concord, Mass., where Thoreau famously lived and worked. Nearly a thousand miles away in Wisconsin, where Leopold gathered his records of blooming plants like wild geranium and marsh marigold, the change is even more striking. In 2012, the warmest spring on record for Wisconsin, plants bloomed on average nearly a month earlier than they did just 67 years earlier when Leopold made his last entry.”

“These historical records provide a snapshot in time and a baseline of sorts against which we can compare more recent records from the period in which climate change has accelerated,” explains Stan Temple, one of the co-authors of the study and an emeritus UW-Madison professor of wildlife ecology.

While this study certainly isn’t the first that documents the close relationship “between temperature and flowering dates and the trend toward climate-driven early blooming, it is the first to suggest that the trend in flowering plants may continue beyond what has been observed in controlled studies. The work thus has important implications for predicting plant responses to changing climate, essential for plants such as fruit trees, which are highly susceptible to the vagaries of climate and weather.”

“We used relationships revealed in historical records to predict how 47 species of native plants would respond to unprecedented spring temperatures, but that has only been possible because naturalists, past and present, kept good records of what they observed in nature,” Temple says.

“Importantly, the results give scientists a peek into the subtleties of ecological change in response to climate change. Flowering of native plants, a harbinger of spring in the world’s temperate regions, signals the start of the growing season. Changes in the timing of flowering have broad implications for the animals and insects that depend on the plants.”


“Earlier blooming exposes plants to a greater risk of experiencing cold snaps that can damage blossoms and prevent fruiting,” says Temple. “The Door County (Wisconsin) cherry crop was ruined in 2012 because the trees bloomed very early in response to record-breaking warmth only to be hit by subsequent frost.”

The new research was focused on the very specific and detailed “phenological records of 32 native plant species in Concord, Mass., kept between 1852 and 1858 by Thoreau, a pioneering naturalist best known as the author of ‘Walden,’ as well as later records. A second data set of flowering times for 23 species in southern Wisconsin was compiled by Leopold, a renowned wildlife ecologist at the University of Wisconsin and author of ‘A Sand County Almanac.’ Leopold and his students gathered their data in Dane and Sauk Counties between 1935 and 1945. From 1977 until she died in 2011, Aldo Leopold’s daughter Nina Leopold Bradley resumed the collection of phenological records near the Leopold Shack.”

“Both Thoreau and Leopold were part of the 19th century naturalist movement in which individuals often kept meticulous daily journals recording the things they observed in nature,” says Temple. “Most of those journals have been lost over time, but Thoreau and Leopold were famous writers, and their journals have been preserved, providing us with unparalleled historical data.”

“Comparing modern observations with those gathered by Leopold shows that in 1942, when the mean spring temperature in southern Wisconsin was 48 degrees Fahrenheit, black cherry bloomed on May 31. In 2012, with a mean spring temperature of 54 degrees Fahrenheit, black cherry blooms were observed as early as May 6. In 1942, Leopold’s notes show the woodland wildflower bloodroot blooming on April 12. In 2012, bloodroot was first observed blossoming March 17.”

When taken as one, “these data sets provide a unique record of flowering trends in the eastern United States over a 161-year period.”

“Leopold and Thoreau had no idea their observations would help us understand responses to human-caused climate change,” says Temple. “But Leopold knew his records might be useful in retrospect when he wrote: ‘Keeping records enhances the pleasure of the search, and the chance of finding order and meaning in these events.'”

The trend of earlier flowering times, while not immediately a problem, will likely lead to vast changes in the many forms of agriculture that are dependent upon the plant blooming. It’s difficult to say what the exact effects will be, but none of the likely effects are positive, and will probably lead to lower agricultural output.

The new research was just published online in the journal PLoS One.

Source: University of Wisconsin-Madison

Image Credits: Jeff Miller; Service Berries via Wikimedia Commons

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