Natural History Highlight - National Museum of Natural History

Smithsonian Institution National Museum of Natural History, Natural History Highlight

Scientists at the Smithsonian’s National Museum of Natural
History Find Global Warming to be Major Factor in
Early Blossoming Flowers in Washington

NMNH Botanist Stanwyn Shetler and colleagues Mones Abu-Asab, Paul Peterson, and Sylvia Stone Orli have analyzed 30 years of observations about the first dates of blossoming for 100 species of plants common to the Washington, DC area. They have found that the rise in the region's average minimum temperatures is producing earlier flowering in 89 of the 100 species observed. On average, the plants are blossoming 4.5 days earlier in 2000 than in 1970 - and for Washington's famous cherry trees, this means that the cherry blossoms are now arriving a week earlier than 30 years ago.

Houstonia caerulea (Bluets). Photo by Elaine Haug The scientists examined botanical data collected at the Smithsonian's Department of Botany by more than 125 individuals over a 30-year period beginning in 1970 in order to reach their findings. Data were obtained at sites in Washington, D.C.; Arlington, Virginia; Beltsville and Silver Spring, Maryland; and other regional locations.

Prunus X yedoensis (Yoshino Cherry Tree). Photo by S. G. Shetler "This trend of earlier flowering is consistent with what we know about the effects of global warming," said Dr. Stanwyn Shetler. "When we compared the records from the Smithsonian study with local, long-term temperature records we discovered statistically significant correlations. The minimum temperature has been going up over these years and the early arrival of the cherry blossoms appears to be one of the results."

Using data from the National Park Service, Shetler, Abu-Asab, Peterson and Orli also examined two predominant species of Japanese flowering cherries located near the Tidal Basin in Washington, DC, which have been blooming on earlier dates over the past 30 years. The Oriental cherry blossom (Prunus serrulata) and the Yoshino cherry blossom (Prunus x yedoensis) have been reaching peak bloom six and seven days earlier since the 1970s, respectively. This year, the Yoshino variety reached peak bloom on March 20, the second earliest date on record.
The average peak bloom date April 4.

Claytonia virginica (Spring Beauty). Photo by Elaine Haug Analysis of the Smithsonian database infers that early blooming is not a phenomenon isolated to cherry blossoms. Among the 100 plant species (2 cherry + 98 native or naturalized species) analyzed by the scientists, 89 have shown a consistent trend of flowering earlier and earlier each year. Eleven species in the study actually show a reverse trend by blooming later, including the Japanese honeysuckle, which blooms on average 10.4 days later and the Dutchman's-breeches, opening 3.2 days later.

The consequences of the environmental changes indicated by the earlier flowering could be significant, as Shetler explained, "Based on this study, we can expect a gradually expanding growing season, which may be lengthened at both ends if warmer temperatures prolong the end of summers as well. Over a long period the species composition of our local flora could change. Species like the sugar maple that require a long cold period may die out in our region. Invasive alien species, especially from more southern climes, may become more and more of a problem. Weedy species like false-strawberry that can bloom through relatively mild winters could spread. If these trends continue, persons with allergy problems will experience them earlier because some of the first plants to bloom are wind-pollinated trees, such as the American elm and common alder."

Uvularia perfolia (Bellwort). Photo by Elaine Haug NMNH botanists will continue to study the flowering patterns of local plant species in order to contribute to the general understanding of the effects of global warming.

Shetler and Orli are also the authors of the new Annotated Checklist of the Vascular Plants of the Washington-Baltimore Area (Part I - Ferns, Fern Allies, Gymnosperms, and Dicotyledons). Its publication represents the initial step toward providing the first inventory of the vascular flora in the Washington, D.C. area in more than 50 years.

Asimina triloba (Paw Paw). Photo by Elaine Haug

To learn more about Early Blossoming research and Spring Flowering Plants visit these links:

Department of Botany Website
Spring Flowering Records,
from the Department of Botany

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