New Yorkers do things faster than their country cousins. So do our trees, it turns out. According to a new study led by a young Columbia University graduate named Stephanie Y. Searle, red-oak acorns planted in Central Park grow eight times faster than those planted way upstate. Apparently, a phenomenon called the “heat island effect” helps them more than offset the geographic disadvantages of putting down roots here.
Blacktopped areas like ours soak up the sun’s rays by day and release the stored energy overnight, thus making cities a few degrees warmer than the surrounding areas. (Our high concentration of air conditioners, all pouring hot air out their backsides, may also raise the temperature some.) To isolate that variable, Searle and her team set out potted acorns in a variety of environments, from Central Park to the Ashokan reservoir near Woodstock, then repeated the experiment in two identical glass cabinets, one with temperature settings that mimicked New York City’s, the other set to that of a rural area upstate. The New York seedlings took off as if running to catch a G train. Moreover, they put their boosted energy into making extra leaves rather than extra roots. “That’s compound interest,” notes Columbia professor Kevin Griffin, one of the study’s authors. “The more leaves you have, the more photosynthesis you can do, the more leaves you can make.” Eventually, the growth rate slows down, a finding verified by the lack of sequoia-size trees poking through our sidewalks.
If you are environmentally inclined, the study’s results may sound disconcerting—they imply, yet again, that we’re massively screwing up the natural world—but another way to look at them is as Head Start for saplings. Neil Calvanese, the Central Park Conservancy’s vice-president of operations and master of all things arboreal, explains that New York is a hard place to be a tree. “It’s a stressful environment, from drought to low levels of organic matter in the soil,” he says. “You know, in the Park, we have 38 million visitors a year, and the number of people trampling on it is an issue. For a street tree, in a pit, it needs all the benefits it can get. You have dogs urinating on it; the roots are compacted. If the heat-island effect helps it put a little growth on there, it’s probably a good thing.” Calvanese is, as ever, watching his trees with a keen if skeptical eye. “This year, we had a lot of rain, and a long growing season. You know, it’s hard for me to measure whether it’s any faster. I mean, trees do grow.”
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