Trees Grow Faster in Cities

can you repost the article url? , it doesnt open.

I see that and will copy and post the entire article.

Trees grow faster in the city
Ozone pollution stunts suburban saplings.
10 July 2003
MICHAEL HOPKIN


Ozone can fall to zero in the heart of a city.
© Corbis



Things really are bigger in New York. Even the trees. Those in the Big Apple's core grow larger than those in the surrounding suburbs, researchers have discovered1. Surprisingly, the difference is down to pollution.

For three years Jillian Gregg of the US Environmental Protection Agency in Corvallis, Oregon and her colleagues tracked the growth of identical eastern cottonwoods (Populus deltoides) planted in New York City and at nearby rural sites on Long Island and the Hudson valley.

"They started about six inches high," recalls Gregg. "The ones in the city ended up taller than me; they were only up to my waist in the country." Variables such as soil composition, temperature and carbon dioxide levels could not account for the difference.

The crucial factor, calculates Gregg's group, is exposure to ozone. Levels of this pollutant frequently fall almost to zero in a city's heart, while remaining higher in the country.

"Ozone is probably the most important plant pollutant in the United States," agrees John Lawrence of the US Department of Agriculture's Forest Service in Corvallis, Oregon. The highly reactive form of oxygen stunts plant growth, and can prevent flowering.

Ironically, ozone is generated when sunlight reacts with pollutants, such as the gases in car exhausts. But because it's so reactive, leftover pollutants can scrub city centres clean of ozone, says Gregg. Oxides of nitrogen, for example, react with ozone, reducing levels to below those in the South Pole's famed ozone hole.

In New York's leafy environs, on the other hand, ozone can climb to high levels. In the absence of other pollutants with which to react, it hangs around for longer.

Tens of kilometres up in the stratosphere, ozone protects us from the Sun's ultraviolet radiation. But ground-level ozone can damage the environment and our health. The gas can exacerbate human respiratory ailments such as asthma, for example.

Any place where
you have lots
of automobiles
generates ozone
Eva Pell
Pennsylvania State University



The US East Coast is a known hotspot for ozone pollution. But will cities elsewhere inflict a similar fate on their suburbs? Not necessarily, says plant physiologist Eva Pell of Pennsylvania State University in Philadelphia.

"Any place where you have lots of automobiles generates ozone, but in some places you will have bigger problems than others," Pell predicts. A city's prevailing air movements can determine whether the local countryside is swamped with its pollutants.

Mountains surrounding Los Angeles, for example, may spare much of southern California the worst ravages of ozone pollution. "Los Angeles' air is hemmed in and tends to stagnate," Pell says.


References
Gregg, J. W., Jones, C. G. & Dawson, T. E. Urbanization effects on tree growth in the vicinity of New York City. Nature, 424, 183 - 187, (2003). |Article|


© Nature News Service / Macmillan Magazines Ltd 2003



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Do people also grow faster, under the same conditions?

It isn't that the trees in the city are any better, it's just that the trees in the country are worn out from the long commute.

Very funny. The links appear to be identical, but I couldn't get it from here either. So try these:

http://www.nature.com/nsu/030707/030707-6.html

http://www.nature.com/nature/

It's the fact that the air is loaded with high levels of radioactive carbon, which makes the trees more "active">

People may grow faster, but they also die faster. c.i.

Im sorry, Ive gotta know how theyve discounted other factors like CO2.

That was one giant city and region around it. Assuming they are right for all trees in all cities, quite an assumption, some trees in cities have quite short lives; in particular street trees planted in small tree wells, surrounded by quite compacted unaerated soil, often with poor drainage, many times getting little water, scarred by various means including sometimes cute iron cages that eventually bind the trunk...and wafted about with various noxious fumes, they deal with a lot of obstacles.

The 'weather specialists' at Environment Canada have been commenting on part of this before - that is, the air quality in the suburbs and outlying towns being worse in Toronto, than it is in Toronto itself. It's hard to understand how it happens, but I can vouch for the breathing being easier here than in the suburbs. I always thought it was because all of the small factories etc. had left the city over the past 30 years. I guess it has to be more complicated than that.

Except for in Santa Ana wind conditions, the Los Angeles basin's smog has historically gone east..to the San Gabriel Valley, east with the prevailing winds, and held in by mountains. Before years and years of efforts to lessen smog, this was all very visible to the nekkid eye.

osso, I remember flying into LAX many times when you could see the black smog covering most of the city, but not lately. c.i.

It was heaviest, I believe, right between the late forties and mid fifties, abating greatly in recent years by various measures.

I used to live in Venice, by the beach. When Santa Ana winds came, the smog stopped for a while by the beach, along with lots of styrofoam cups at the shoreline.

I hadn't thought of it until Lovey mentioned it, but when i get off a plane at Pearson, which is "in the 'burbs" nearer to Mississauga than Tarana, i can hardly breathe the air. I don't like the air in the city, but is not as bad as it is at the airport, and her remark may explain that . (I acknowledge that smoking two packs of Camels a day doesn't help, but i don't have the shortness of breath in the small town where i reside that i do in Tarana.)

Trees in the city have to be bigger and tougher and meaner or they'll get trampled on. Gotta be the meanest tree in the 'wood'.