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Trees benefit from radiant heat and nutrients in urban areas

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April 25, 2012

Seedlings did eight times better in New York City's Central Park than at comparable suburb...

Seedlings did eight times better in New York City's Central Park than at comparable suburban and rural sites (Photo via Shutterstock)

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Many people view urban areas as hostile for plants – concrete stifles root growth, and pollution from vehicles makes it difficult to gain nutrients. A study conducted by The Earth Institute at Columbia University not only discredits those theories, however, but suggests that urban environments have a lot to offer plants to promote growth.

To conduct the research, The Earth Institute researchers planted seedlings in the spring of 2007 and 2008 in three sites around New York. Those locations included an area in northeastern Central Park, near 105th street; in two forest plots in the suburban Hudson Valley; and in more rural surroundings near the Ashokan Reservoir in the Catskill foothills, about 100 miles (161 km) north of Manhattan. Over a five-year period, researchers observed an eight-fold increase in biomass in the urban-grown seedlings.

Researchers attribute the increased growth to high temperatures (particularly at night), carbon dioxide concentrations and atmospheric nitrogen deposition. Saplings planted in Central Park developed a lower root-to-shoot ratio, which reduced below-ground carbon costs to the plant. To compensate for the root development, urban seedlings allocated more growth to leaves than the rural-grown seedlings. This resulted in a ten-fold greater photosynthetic area but the same photosynthetic capacity of foliage as the rural plants.

Barnard College student Acadia Roher counts leaves of experimental red oak seedlings at La...

Barnard College student Acadia Roher counts leaves of experimental red oak seedlings at Lamont-Doherty Earth Observatory (Photo: Alisa Frohman)

The findings mark a step toward understanding how nature and urban environments mix. "With human influence spreading across the globe, nature and urban environments are inseparable. The key is that plants can adapt to these changes in their environments, and in this case, really thrive in a human environment," said Stephanie Searle, lead author on a report of the study. Searle is currently a researcher at the International Council on Clean Transportation in Washington DC.

The report's authors weren't surprised by the results. "Our hypothesis was that the oak seedlings would grow faster in the city due to the higher nighttime temperatures," said Searle. Two previous studies on growth of poplar trees in Biosphere 2 conducted by Principle Investigator Kevin Griffin and co-author Matthew Turnbull, plus a previous study on poplar growth in urban environments by Jill Gregg, laid the groundwork.

The research did uncover new findings, however. "We were surprised at the magnitude of difference in growth between trees at the urban versus rural sites," Searle said. "Also, we had hypothesized that the urban seedlings would grow faster specifically because of their higher photosynthetic capacity boosted by higher temperatures, and this turned out not to be true; these plants got a head start by simply investing more resources in the leaves rather than roots compared to the rural plants."

While the findings reinforce the importance and potential of trees and other plantings in urban environments, many cities including New York City already make great efforts to create green spaces. Central park's 843 acres (341 hectares) are landscaped with trees, though many were knocked down in severe lightening storms in the summer of 2009.

"We believe that the 'urban heat island' effect may help trees in the city grow faster and thrive, but most trees in New York City are planted, so the fact that there are so many trees is really thanks to a great job by the NYC Department of Parks and Recreation," Searle commented.

Now it's up to New York City – as well as other urban areas – to capitalize on the advantages of tree growth, and keep cities green.

The paper on the research was recently published in the journal Tree Physiology.

Source: The Earth Institute at Columbia University

About the Author
Enid Burns Enid began her freelance writing career reviewing video games after spending several hundred dollars upgrading a DOS-based machine to get Syndicate to run. Since then she's added coverage of mobile phones, consumer electronics and online advertising to her writing portfolio. Essentially, she's fascinated by shiny objects and making them light up.   All articles by Enid Burns
6 Comments

And don't forget that trees and agricultural plants benefit from high temps, but also a higher atmoshpheric CO2. The Jurassic period 160 million years ago had a CO2 that was 10x higher than now, and the Earth was a huge Dinosaur filled hot jungle filled with diversity of life...(except human life). These ancient periods were fantastic for plant growth, and of course, what gave us the coal and oil deposits we enjoy now...and we are giving back the CO2 that was locked in those resources millions of years ago... It shouldn't get hotter than 22C, on average over the coming centuries. ;)

Doc

Matt Rings
26th April, 2012 @ 10:20 am PDT

An accelerated increase in canopy biomass combined with slower than normal root development does not make for a healthy tree. It is also a potential liability, especially in an urban environment.

treeguy
26th April, 2012 @ 12:31 pm PDT

Pay no attention to the oil money behind this study... This is hilarious. Next thing you know they will tell us plants love car exhaust. Notice they planted the trees in Central Park, LOFLMAO, the most NON-city part of NYC.

You can tell how plants fair in urban environments by looking at all the dead and sickly vegitation on the side of the roads you drive on.

Charles Michael Couch
26th April, 2012 @ 02:08 pm PDT

A second to treeguy's comment. An anecdote: Years ago, my mother in law started tomato seedlings in jiffy 7 pots. Unfortunately, she forgot to remove the membrane from around the root-balls before transplanting them out in the garden. She was sold on jiffy 7's, those plants grew faster and taller than she could believe...until the first summer thunderstorm. When she went out to clean up the garden, she found all of the tomatoes toppled over: the roots had never grown out of the jiffy 7 pots.

Another issue is that there is a difference between urban temperate and urban mediterranean, subtropical or desert. The heat-island effect becomes a liability rather than a benefit in places like Los Angeles, Miami and Phoenix.

Ryan Gyurkovitz
27th April, 2012 @ 07:11 am PDT

Mr. Gyurkovitz,

You so correctly noted: "The heat-island effect becomes a liability rather than a benefit in places like Los Angeles, Miami and Phoenix." As I've noted many times in the past: "The major selling point of Hydrogen Powered vehicles is? They only emit water vapor! And where do they operate? On concrete or asphalt covered surfaces, acting as heat sinks that create updrafts that send the vapor skyward into the atmosphere, thereby contributing to a further "Warming" of the planet! (Think of L.A. or NYC as a Louisiana Swamp in August. If the alarmists are right, that is."

Myron J. Poltroonian
27th April, 2012 @ 10:52 am PDT

These results cannot be extrapolated to the entire city and they can be misleading. How do trees will grow up along the streets where the environmental contitions and the soil is totally different, for example? It is not the same to plant the seedlings in a park where rain can infiltrate and there are still a viable nutrient cycling.

Vagner L. Camilotti
5th August, 2013 @ 05:25 am PDT
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