On February 2, 1887, the people of Punxsutawney, Pennsylvania, sought the advice of a groundhog to anticipate the coming of spring, which marked the very first official Groundhog Day celebration. Although our skills in seasonal prediction remain limited, recent research promises to enhance the reliability of seasonal forecasting significantly.
On February 2, 1887, in Punxsutawney, Pennsylvania, locals turned to a large rodent to predict when spring would arrive, signaling the inaugural Groundhog Day celebration. Rob Guralnick, curator of biodiversity informatics at the Florida Museum of Natural History, believes our ability to forecast seasonal changes has not notably advanced since that time.
“We can’t accurately predict if spring will come early or late nearly as well as we forecast the weather,” he stated.
Weather influences the initiation and conclusion of seasons, but it’s equally critical to understand how plants and animals respond to these shifts, a field known as phenology. While meteorologists can reliably forecast temperatures months ahead, predicting when trees will begin to sprout leaves across their various habitats often leaves scientists puzzled.
The complexity of issues like climate change further complicates these predictions.
However, a recent study in the journal Communications Earth & Environment aims to make seasonal forecasts less daunting and more reliable. The researchers refined existing phenology prediction methods and incorporated a metric for how quickly spring temperatures rise in specific areas. This advancement allowed them to forecast how the timing of leaf and flower growth has shifted over the last 150 years.
Plant species in the U.S. are now blooming three to four weeks earlier than they did a century and a half ago.
This significant discovery was sparked by the rediscovery of an outdated 19th-century report with extensive phenological data on various plants and animals in the eastern U.S. This collection represents an early attempt organized by the Smithsonian Institution to track biological patterns in the U.S. through volunteer contributions, making it the nation’s first phenology-based citizen science project.
Using historical growth data as a baseline, the authors validated their equations by predicting the changes in plant growth timing from the 1850s to 17 years later. They then compared these predictions with contemporary data to assess their accuracy.
Theresa Crimmins, director of the USA National Phenology Network and co-author of the study, discovered the old report while working on a chapter about phenology. “I found this old document rich in data. Most referenced reports were only summaries,” she said.
The report stemmed from a brief citizen science initiative set up by the Smithsonian Institution aimed at observing seasonal changes and was released in two volumes by the U.S. Patent Office. The second volume, detailing plant and animal data, faced publication delays due to the extensive number of official documents produced during the Civil War. Once published, it included information on plant growth from Michigan to Florida and as far west as California.
“This is the oldest dataset we have for large-scale phenology, and the difference from then to now is remarkable,” Guralnick noted.
To verify their findings, the authors began by analyzing growth cycles from the historical dataset against observations of 18 plant species made in the last decade. They expected changes caused by climate change but were shocked by the extent of the differences observed.
“All 18 species showcased earlier leaf growth and flowering patterns,” Crimmins explained. “On average, these events are occurring over three weeks sooner than they did in the past, with some species blooming more than a month earlier.”
It is well-recognized that global warming has resulted in earlier springs and prolonged summers, but confirming this over such an extended period is uncommon due to the lack of historical data.
The rate of warming in spring affects when plants develop leaves and flowers.
However, not every region or species in the eastern U.S. has seen the same level of change in the past 175 years. For instance, phenology has advanced more significantly in the northeastern U.S. compared to the Southeast. Traditional equations used to forecast leaf growth and blooming have struggled to account for these varying trends.
Typically, scientists utilize two key factors to predict phenology: the geographical location of the plant and its warm weather requirements for becoming active. While effective for specific species in confined areas, this method is less useful for broad changes, such as when spring arrives for an entire forest.
This challenge is often blamed on substantial variability both within and between species.
For example, a maple tree will react differently than an oak, and even an oak will respond diversely depending on its location.
Climate change introduces further complexities.
“There’s not only variation across species but also differences in warming rates at various latitudes. Higher latitudes are experiencing faster warming,” noted co-author Lindsay Campbell, assistant professor at the University of Florida’s Florida Medical Entomology Laboratory.
Nevertheless, even when accounting for these differences in warming rates, some patterns remain perplexing. For instance, red maples, typically among the earliest blooming plants in eastern North America, produce vibrant crimson flowers in late winter and early spring, while pink azaleas bloom later in mid-spring. Yet, under certain conditions, it is not uncommon for the usually later-blooming azaleas to flower before early-blooming maples when growing in the same latitude.
Guralnick theorized there might be a missing element that could clarify these trends. He proposed adding a measurement for “warming velocity,” indicating how quickly spring temperatures rise, to the location and temperature needs of the plants. Areas adjacent to large bodies of water tend to warm more slowly in spring because water heats up more slowly than air, and retains heat longer, often leading to milder winters. Guralnick generated initial ideas on paper and collaborated with Crimmins and Campbell to refine this concept and develop a model that integrates warming velocity with warm requirements as predictors for phenology.
To validate this concept, two interns, Michaela Keys and Carolyn Davis, digitized the historical data from the Smithsonian report. Co-author Erin Grady, a graduate student in the UF biology department, compiled modern data collected by citizen scientists available through iNaturalist and the National Phenology Network.
After analyzing the data, their hunch was validated. Including warming velocity led to predictions aligning well with the observed patterns.
Furthermore, this approach provided a rationale for previously inexplicable patterns, such as later-blooming plants surpassing early bloomers. In rapidly warming regions, a typically late-blooming pink azalea may produce flowers before a maple in an area where temperatures rise more slowly.
The enhanced precision in forecasting ecosystem cycles could aid conservationists in their planning efforts. With continuing global temperature increases due to climate change, plant and animal species are not only adjusting their timing but are also changing their geographical distributions, according to Guralnick.
“I used to be doubtful about our capacity to predict what our world will look like shortly, but I believe we are making progress by adopting a more comprehensive approach and understanding the underlying processes. Doing so will help us better manage the biodiversity we still have,” he concluded.
