Predicting how climate change will alter plant growth cycles

On February 2, 1887, residents of Punxsutawney, Pennsylvania turned to a large rodent to predict the arrival of spring, marking the first official Groundhog Day. 

Over 130 years later, according to Rob Guralnick, curator of biodiversity informatics at the Florida Museum of Natural History, we haven’t made much progress in predicting seasonal changes.

“We can’t generate good forecasts for whether spring will arrive early or late next year nearly as well as we can make predictions about the weather,” Guralnick said.

Predicting the climate response of plants

Weather patterns undoubtedly influence the seasons, but how plants and animals respond to those changes – a field called phenology – is equally important. 

While meteorologists can reliably forecast temperatures months ahead, predicting when plants will sprout leaves or flowers remains a challenge. Add climate change into the mix, and the puzzle becomes even harder to solve.

However, a new study published in the journal Communications Earth & Environment offers promising advancements. 

By improving existing methods and incorporating the rate at which springtime temperatures rise, the study accurately predicts how seasonal cycles have shifted over the past 150 years.

Plants bloom earlier in a warmer climate

The breakthrough came after researchers rediscovered a forgotten 19th-century report containing thousands of phenological observations across the eastern United States. 

This report – the earliest citizen science project organized by the Smithsonian Institution – documented when plants and animals became active across regions stretching from Michigan to Florida.

Theresa Crimmins, director of the USA National Phenology Network and co-author of the study, stumbled upon the report while researching for a book chapter. 

“I dug up this old document and realized there was actual data in it. Most of the other reports that had been referenced were just summaries,” said Crimmins.

The team used these historical records as a baseline. By comparing them with modern observations, they uncovered striking shifts.

“All 18 species advanced their leaf growth and flowering phenology,” Crimmins explained. “On average, it’s occurring more than three weeks earlier than it did in the past. There are some species that are flowering more than a month earlier.”

The findings confirm what scientists suspected: global warming has led to earlier springs and longer summers. Yet the study’s use of historical data over such an extensive time period is rare, making the results particularly compelling.

Some regions are changing faster than others

Interestingly, not all areas of the U.S. have experienced the same shifts. Phenology in the Northeast has advanced far more than in the Southeast, highlighting variations in the rate of change across latitudes. 

Traditional models used to predict plant activity focus on two main variables: a plant’s location and the amount of warm weather needed for it to grow. While these models work for specific species in localized areas, they struggle to explain broader trends across diverse ecosystems.

“Not only is there variation across species, there’s variation across latitudes in the rate of global warming. Climate is warming faster at higher latitudes,” said co-author Lindsay Campbell, an assistant professor at the University of Florida’s Florida Medical Entomology Laboratory.

These complexities can result in unexpected patterns. For example, red maples, which typically bloom early in spring, may be outpaced by pink azaleas – traditionally later bloomers – if they grow in an area where temperatures rise quickly.

A missing factor: Warming velocity

To solve these mysteries, Guralnick suspected an overlooked factor: the rate at which temperatures increase in spring, also called “warming velocity.” 

Areas near large bodies of water, for example, warm more slowly because water retains heat longer than air. Such regions tend to experience gradual warming and milder winters.

To test this idea, Michaela Keys and Carolyn Davis, two museum interns, digitized the Smithsonian’s historical data. Co-author Erin Grady, a graduate student at the University of Florida, compiled modern observations from citizen science platforms like iNaturalist and the National Phenology Network.

Once the team ran the numbers, the results were clear: adding warming velocity dramatically improved the accuracy of their predictions. It also provided explanations for anomalies like late-blooming plants flowering ahead of early bloomers under certain conditions.

Complex dance between plants and climate change 

These findings have important implications for conservation. As global temperatures continue to rise, species are not only shifting their seasonal cycles but also changing where they live. For conservationists, being able to predict these changes is vital for protecting ecosystems.

“I’ve always been skeptical about whether we’ll be able to predict what the world will look like in the near future, but I think we’re getting better at it as we take a more holistic view and as we get the underlying processes nailed down,” Guralnick said. “Doing so helps us manage the diversity we have left.”

By combining historical observations with modern data and improved models, scientists are inching closer to understanding the complex dance between plants, temperature, and climate change. 

As the planet warms, tools like these will be crucial for anticipating and mitigating the impacts of a shifting world.

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