09/26/2014

Sprouting a Forest in the City

5:43 minutes

Rich Hallett’s job today is collecting leaves from the tops of trees—and he has an unusual way of doing it.

He has an eight-foot-tall sling shot. He’s shooting a bean bag connected to a nylon string 30 feet in the air towards the branches of a Willow oak tree. But he keeps missing his target.

When he finally nails it—if he finally nails it—the bag will dangle over a branch.

He pulls on the string and sends a clump of leaves falling down.

It’s his first shot of the season. He’s still working out the kinks. “Hopefully we’ll get back on our game,” Hallett says.

Hallett is a research ecologist with the U.S. Forest Service. He needs the leaves to test chloropyhll levels. He wants to measure the tree’s photosynthetic capacity—how much energy it’s producing. It’ll give him an idea about how healthy this tree is.

Today, he’s testing leaves at the Frank M. Charles Memorial Park. It’s just a 10-minute walk from JFK airport in Queens. You can watch the planes take off from just across the bay.

Hallett used to study rural forests. He’d hike through the backcountry, sampling trees in remote places like Alaska’s Tongass National Park and the Green Mountains in Vermont. The trees there can get much taller than this 61-foot willow oak. Sampling those leaves requires a little more precision.

“The most efficient way method is a shotgun. So we used a 12-gauge shotgun. We used No. 4 birdshot. And we used steel shot and never lead,” Hallett says. “And obviously, the shotgun is not appropriate for Queens.”

Queens might seem like an unlikely place for a forester, but Hallett says trees in the city are fascinating because they have to outperform their country counterparts.

“Working with trees in the city and realizing we expect more from the trees,” he says. “They have to be harder working than the trees in our forests and mountains. They have to put up with soils that are man-made that they didn’t evolve growing in, they have harsh conditions—chemistry, exhaust from cars, and just a lot of stress.”

Hallett’s goal is to create an urban forest, getting trees to grow among the concrete and skyscrapers of New York City. In the past, the city had two different categories for trees: it was either dead or alive. Hallett and fellow ecologist Nancy Sonti are collecting detailed data to get a clear picture of how tough city living is impacting these trees.

“We’re working to quantify that information to truly understand how trees interact with air quality with greenhouse gas emissions, storm water capture in tree pits, and just general hydrology,” says Sonti.

New York City officials are also interested in that data. Trees soak up harmful greenhouse gas emissions and help offset the “urban heat island” effect.

You might have experienced this effect. On a summer night, have you ever stepped onto the pavement and felt like the air is warmer? That warmth comes from the heat that streets, buildings,and sidewalks have soaked up during the day. At night, all those structures release the heat. That leads to warmer temperatures, higher air pollution levels and increased energy use.

It’s one reason for the city-wide campaign to plant one million trees over the next decade.

Hallett and Sonti are studying “street trees”—that’s the technical name for the trees you see growing out of the sidewalks. Oak, maple, black cherry and gingko are some of the common species in the city.

We’re standing at the base of a red maple that was flooded by Hurricane Sandy. It looks like it’s in good shape. But to really find out how stessed this tree is, they need to look at different indicators like leaf discoloration, twig growth and photosynthetic capacity.

That’s brings us back to the leaves that Hallett was pulling off of the trees.

“Based upon these numbers so far, this tree is not performing very well,” he says. “This is surprising. I would have expected it to be better. I’m still leaning towards a recovery scenario for that tree, but maybe that’s because I’m an optimist.”

They’re not sure exactly why this tree isn’t doing better. It could be that they’re measuring it a few months earlier than last year or maybe the harsh winter weather took its toll. They’ll keep measuring it each year to find out.

And even if this tree doesn’t make it, but there’s a bigger vision beyond individual street trees. New York City still has 100,000 more trees to plant to reach that million-tree goal.

“It’s nice to have some more equality on the distribution of our street tree population at least,” says Sonti. “A lot of those trees are still very small and as they mature i think it really will change the face of our urban forest.”

Ecologists like Rich Hallett and Nancy Sonti are just piecing together how complicated that urban forest ecosystem really is. And what they learn today, could help change the concrete jungle into something…a little greener.

Segment Guests

Rich Hallett

Rich Hallett is a research ecologist at the NYC Urban Field Station at the U.S. Forest Service in New York, New York.

Nancy Sonti

Nancy Sonti is an ecologist at the NYC Urban Field Station at the U.S. Forest Service in New York, New York.

Meet the Producer

About Alexa Lim

Alexa Lim is a producer for Science Friday. Her favorite stories involve space, sound, and strange animal discoveries.