Smithsonian Scientists Find Global Warming to be Major Factor in Early Blossoming Flowers in Washington

Cherry blossoms now arrive a week earlier than 30 years ago

WASHINGTON, D.C. - Smithsonian scientists have evidence that Washington's famous cherry trees are blooming on the average seven days earlier than 30 years ago, apparently due to global warming. The Smithsonian's National Museum of Natural History released today background on the results of a 30-year study of flowering plant species common in the Washington, D.C. metro area. The study conducted by the museum's Department of Botany indicates that the rise in the region's average minimum temperatures is producing earlier flowering in 89 of the 100 common plant species investigated. On average, flowering plants are blossoming 4.5 days earlier in 2000 than in 1970. The study suggests that the trend toward earlier blooming of flowering plants may be a result of global warming.

Smithsonian scientists Stanwyn Shetler, Mones Abu-Asab, Paul Peterson, and Sylvia Stone Orli examined botanical data collected by more than 125 individuals over a 30-year period beginning in 1970 in order to reach their findings. Data was obtained at sites in Washington, D.C., Arlington, Virginia, Beltsville, and Silver Spring, Maryland and other regional locations.

"This trend of earlier flowering is consistent with what we know about the effects of global warming," said Dr. Stanwyn Shetler, botanist with the Smithsonian's National Museum of Natural History. "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."

Utilizing data from the National Park Service, Smithsonian scientists examined two predominant species of Japanese flowering cherries located near the Tidal Basin in Washington, D.C. which have been blooming on earlier dates over the past 30 years. The Oriental cherry blossom (Prunus serrulata) and the Yoshino cherry blossom (Prunus 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 date to bloom is April 4.

Analysis of the database infers that early blooming is not a phenomenon isolated to cherry blossoms. Among the 100 native and naturalized plant species analyzed by the researchers, 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 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 the warmer temperatures prolong the end of summer 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 throughout 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."

Smithsonian 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 the authors of the new Annotated Checklist of the Vascular Plants of the Washington-Baltimore Area (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. Shetler has been responsible for the taxonomy and nomenclature and Orli for the database. The publication will be of vital interest to botanists, as well as, horticulturists and naturalists. A Web site for the Flora of the Washington-Baltimore Area is maintained where the database can be searched at

The National Museum of Natural History, located at 10th Street and Constitution Avenue, N.W., is open daily from 10 a.m. to 5:30 p.m. Admission is free. For further information, call (202) 357-2700, TTY (202) 357-1729, or visit the museum's home page on the World Wide Web at For recorded information in Spanish, call (202) 633-9126.