MS. REBECCA SHEIR
We turn now to trees. In Washington, D.C., as in a lot of cities, certain kinds of trees tend to be particularly popular. Think American elms or Bradford pear trees. But sometimes these trees aren't the best barriers to all that exhaust, road salt and other pollution that urban life brings. Nor do they necessarily promote biodiversity in their urban eco system.
MS. REBECCA SHEIR
This week the non-profit organization, K.C. Trees, hosted an entire symposium on this very issue. Environment reporter Jonathan Wilson caught up with one of the speakers, National Arboretum research geneticist Richard Olsen.
DR. RICHARD OLSEN
The first thing that comes to mind is people think of establishing a resilient urban forest. The lessons from the past in urban forest has been when you plant a monoculture of species -- and in the case of like American elm, where we were so dependent on American elm -- and then you have an introduction of an exotic pest or a disease that affects that species you have a tremendous loss of the urban forest at one time. So the first thing that comes to mind is resilience. And you need diversity so that one new pest or disease doesn't wipe out a significant portion of your tree canopy.
MR. JONATHAN WILSON
Right now, I mean like in Washington, for example, would you say the city's doing a pretty good job of planting the trees that people in your field would like to see get planted? And, you know, other communities in our region? Do you think that we're doing an okay job of planting the right types of trees?
They're doing a pretty good job, I think, in terms of understanding the need for diversity. It's always a tough lesson. You can only plant what's available in the nursery industry. That's a good lesson. The nursery industry is only going to produce what they can sell. And I think with emerald ash borer and Dutch elm disease that people are certainly learning that diversity is key. And also with the rise of urban ecology, you know, prior to about 15, 20 years ago, ecologists stayed away from the cities.
That was not ecology. That was the urban environment. And people are starting to realize that with urbanization that it is an environment, it is an ecosystem and we have to understand how it functions.
In terms of deciding -- let's say I'm in the urban forestry department, I'm trying to decide what kind of trees get planted -- I imagine that aesthetics is a big part of it, but you've also told me that resistance to things like road salt is a huge issue for cities. Talk about that.
The urban environment -- this is a good winter to explain this. We put down a lot of deicing salts in the winter. And that sort of -- when you get these melts and you get is right about springtime, all that salt has to go somewhere. And it's going into the beds. If you don't have a lot of rain, you don't have a melt, it sits there. It can build up. And then ultimately that is being exposed to the urban trees' roots.
And so you have to look for species that are tolerant. A lot of our urban trees come from the eastern bottomland hardwood forests. So trees that can naturally take low oxygen environments, flooded environments, that's exactly what we have in urban soil. So on top of that you have to throw in, what do we want in society as a tree? And historically we didn't want it to be messy. We want it to have extended appeal. You know, we want it to look good in all four seasons. We want the leaves to just fall off and disappear.
We don't want to have to clean them, you know. We don't want fruit. We don't want slippery flowers. We don't want it to be allergenic. There's all these things we want and then there is the shape. We want them to be tall and narrow because they can't be big and broad anymore. They have to be short, under power lines, so they don't interfere. So we're really asking a lot. And we want it to look good. And that's traditionally what we've asked. You have to be tolerant and you have to look good.
And then sort of the new paradigm, in terms of diversity in the urban forest, is not just the diversity of the tree species itself, but how does it play in the larger ecosystem? Does it contribute value to the urban forest, in terms of these trophic levels? And that's a whole new ballgame. So, in essence, we're saying we want trees to be eaten by insects, so that they support birds and then make the urban environment that much more wonderful. So that's a shift. We've gone from purely ornament, a design feature in the landscape, an aesthetic, to this new aesthetic, which is wouldn't it be great and wonderful if it supported all sorts of wildlife.
That was research geneticist Richard Olsen speaking with Jonathan Wilson, at the National Arboretum's research facility in Beltsville, Md. We have a lot more of their conversation on the web, including the tree species Olsen thinks are on the rise. Just head to metroconnection.org.
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