Replanting the Urban Landscape with Cloned Trees

In cities across the country, governments and nonprofits are spending a lot of time and money adding trees to their urban landscapes. One of the main goals is to plant different types of trees. But many trees being planted are the same genetically--because they're cloned. One scientist says this leaves trees especially susceptible to diseases. The Allegheny Front's Anthony Brino finds, however, that there are two sides to the coin.

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OPEN: In cities across the country, governments and nonprofits are spending a lot of time and money adding trees to their urban landscapes. One of the main goals is to plant different types of trees. But many trees being planted are the same genetically--because theyre cloned. One scientist says this leaves trees especially susceptible to diseases. The Allegheny Frontís Anthony Brino finds, however, that there are two sides to the coin.

ERB: In these pots we probably have eight to ten different species of oak trees, all the acorns collected here in the city.

BRINO: Thatís Matt Erb, of the nonprofit Friends of the Pittsburgh Urban Forest. Heís walking through the nursery on the back porch of the groupís office.

ERB: And you see these are the Chinkapin seedlings, and theyíre growing very well. Chinkapin oak, which is not a very common tree grown by nurseries. We know of a very nice specimen in Allegheny Cemetery as well as Schenley Park. So we collect acorns from those two trees, that we know have thrived in Pittsburghís climate for decades, if not centuries.

BRINO: Over the past two years, Friends of the Pittsburgh Urban Forest has been germinating seeds this way. Theyíre trying to plant 20-thousand trees by 2012. But most trees planted around the country are not grown on back porch nurseries. Theyíre cloned.

Which worries botanist Cynthia Morton.

MORTON: One of the images is right behind you.

BRINO: In her lab at the Carnegie Museum of Natural History, she points to a family tree--of trees.

A few years ago, Morton looked at the DNA of 100-foot-tall London plane sycamores in Pittsburghís Oakland neighborhood. They were planted before World War Two. She found what she calls fabulous genetic diversity. Then, she said she looked at the DNA of young, 20-foot-tall sycamores across the street.

MORTON: And we basically saw that these batches of DNA, these leaf samples from the nurseries from different trees, were all the same. And I said, "Whatís going on here? Somethingís happening."

BRINO: The old sycamores were grown from seed, like the seedlings on Friends of the Pittsburgh Urban Forestís back porch. The young ones came from nurseries, and were cloned. The practice has grown more popular over the past couple decades. Itís relatively simple. You take a cut branch, or whatís called a cutting, and treat it with hormones. Then it grows roots, and you have a seedling physically and genetically identical to the parent.

Morton says nurseries clone because itís cheaper and quicker than growing from seed. They also want to produce trees that look similar, she says. Thatís what customers want. Knowing this, Morton started calling nurseries. She learned that a lot of small, regional nurseries get their trees from just a handful of large nurseries based in the Pacific Northwest.

MORTON: Call them up--Washington and Oregon--and said, "Iím doing a study on genetic diversity." Cling. Would not get any kind of conversation. Called them up again and I said, "I want to plant a bunch of trees in the city of Pittsburgh. Can you tell me, I want to make sure I have nice uniformity in my trees." "Oh, weíve got uniformity for you."

BRINO: In Pennsylvania, the nonprofit TreeVitalize oversees tree planting groups across the state. By 2012, theyíll have spent $7 million, from public and private funding, mostly in Philadelphia and Pittsburgh. And theyíre expanding into 12 other metro areas. A state spokeswoman for TreeVitalize says the reliance on cloning is a little disappointing. Morton says we ignore genetic diversity at our own peril. She compares tree threats in the 1900s among genetically diverse populations to those today.

MORTON: The more we plant these cloned trees, we probably have a problem. If we look at what happened with the chestnut blight and the Dutch elm disease, it took a while for the trees to die. If we look at what happens with the green ash borer, itís five years; itís been widespread from one place to the other. And I think that as we clone more trees and plant them, itís going to be more rapid devastation.

BRINO: But Morton says if nurseries are going to clone, they should at least use DNA from resilient old trees like the London planes in Schenley Park.

MORTON: Weíve got all those old trees out there. Theyíve got fabulous genetic diversity. Theyíve been climbed on. Theyíve been salted on. Theyíve had the worst pollution in the last 100 years. We can take those cuttings and give them more genetic diversity.

BRINO: Back at Friends of the Pittsburgh Urban Forestís office, Erb Dutch elm disease, for instance, is now hitting the West Coast.

ERB: Cities like Seattle and Portland are losing elm trees right now from Dutch elm disease. Fortunately, with genetic diversity of the elm species, there have been a few resistant trees that are now being cloned and incorporated into breeding programs, to help bring that species back as a viable species to plant in streets and parks.

BRINO: So far, Friends of the Pittsburgh Urban Forest has planted close to six-thousand trees. Theyíre also working out a plan with the city government to set up a larger nursery in Point Breeze. You can find them in Pittsburgh Parks almost every week, collecting seeds for their genetic melting pot.

For the Allegheny Front, Iím Anthony Brino.