More than 1 million visitors flock to Washington, D.C. each spring to view the cherry trees. Photo by Rebecca Jacobson.
Every spring in Washington, D.C., the tree paparazzi come out. As the 3,700 ornamental cherry trees along the National Mall and Tidal Basin burst into bloom, more than a million visitors flock to the capital to view the flowering canopies. They cross barriers and climb branches just to capture the perfect shot of the pink and white blossoms. The annual National Cherry Blossom Festival, now in its final week, is a part of Washington tradition.
The iconic trees were a gift from Japan to the United States in 1912 as a symbol of friendship between the two nations. But the stock of original cherry trees is rapidly depleting. Of the original 3,000 gift trees, fewer than 100 still live on the National Mall, said Carol Johnson, a National Mall spokesperson.
Margaret Pooler, research geneticist at the National Arboretum, explains why cloning the trees is necessary. Video by Rebecca Jacobson and Cindy Huang.
Ornamental cherry trees in the United States have an average lifespan of 40 years, made shorter by the stress brought on by the annual flood of visitors, said Dave Kidwell-Slak, a horticulturist at the National Arboretum. Constant traffic compresses the soil around their roots, removing the protective grass and leaving roots exposed. Tourists climb the trees and pluck their branches, scarring the trees, preventing new growth and exposing gaping wounds for bugs and diseases. And Kidwell-Slak fears that warming winters will bring more bugs.
As the trees die, National Parks Service officials sometimes replace them with other cherry trees from U.S. nurseries. But there’s another effort that’s been underway since 1997: cloning the originals.
Japan gave the United States 3,000 ornamental cherry trees as a sign of friendship in 1912. Fewer than 100 of the original trees remain. Photo by Cindy Huang.
In the 1970s Roland Jefferson, a botanist at the National Arboretum and a personal champion of the cherry trees, started taking cuttings of the originals and propagating them himself, fearing that they would be lost forever. By 1979, he had cloned 100 flowering cherry trees. He was also the first person to pen a definitive history of Washington’s cherry trees.
Cloning trees may sound like a major biotech effort, but it’s actually fairly simple, said Margaret Pooler, a geneticist who has been working on cherry trees for the Arboretum. People have been doing it for hundreds of years, she said.
One technique involves cutting “soft wood,” or new tender growths from a late spring branch. Nursery gardeners at the Arboretum wrap the cuttings in wet towels and dip them in a root hormone. Then they incubate them in a warm, moist greenhouse until the stems sprout roots.
Another involves grafting the sapling onto the established roots of another tree, literally highjacking that tree’s roots, Kidwell-Slak said. Genetically, it’s the same tree that was planted in 1912, and it would take generations for trees to see any genetic “drift” between the clones and their original. So scientists could theoretically clone these trees indefinitely, Kidwell-Slak said.
Clones are appealing to horticulturists, Pooler said, for their reliability. The blossoms, the colors, even the bloom times will remain the same from generation to generation.
Cloning the trees isn’t complicated, but it is time and labor intensive. Horticulturists could freeze samples of DNA, but it’s easier to clone the living plant. The saplings have a 70 percent survival rate, and it can take years before they are strong enough to plant outdoors, Pooler said. Since the project began, 500 clones have been created from the gift trees.
But the reasons for cloning the trees are mostly esoteric, Kidwell-Slak said, like keeping a dog’s pedigree. That genetic lineage connects the trees to their past, and allows that heritage to be shared. Kidwell-Slak says the Arboretum has sent clippings of the gift trees to Pittsburgh and North Carolina for cities to plant.
According to Pooler, keeping that lineage preserves a record of the original gift so future horticulturists can keep the line going 40 or 50 years into the future. However, having too many trees of the same family in one park makes the group susceptible to disease. So Pooler has been studying the 1912 trees to create new, resilient hybrids of ornamental cherry trees to strengthen the historic crop.
“Cherry trees are loved,” she said, “We are hanging onto one lineage, but we are also breeding to make wide crosses of species to broaden the base of cherries.”
Charles Birnbaum, founder of the Cultural Landscape Foundation, said there are dozens of other trees and landscapes that need the same preservation and attention as the Tidal Basin cherry trees. Birnbaum calls the cherry blossoms “witness trees,” trees that were a part of history and serve as living reminder of our past. Seeing an inauthentic replica isn’t the same, he said.
“Every tree has a story,” he said. “These are portals to the past. These are like an “Alice in Wonderland” hole that you get to fall into and experience something real.”
Cindy Huang contributed to this report.