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Mature trees store a lot of carbon, so they help reduce global warming. And they provide cooling shade, soak up stormwater, and help purify the air.

So it’s important for cities to know how many trees they have, where they are, and how they’re changing.

Tony Giarrusso at the Georgia Institute of Technology has been monitoring tree cover in Atlanta for more than a decade.

He uses satellite imagery and mapping software to estimate the extent of the city’s tree canopy: “the branches and leaves and trees as seen from above, like out of a plane,” he says.

But he also dives deeper to see what’s happening at the neighborhood level.

For example, several years ago, tree cover in some low-income areas appeared to be expanding. But he found that much of the increase was caused by scrubby trees on vacant lots.

Many of those trees were only temporary because the lots would eventually be developed. And they did not provide the same benefits as big, old hardwood trees.

“So a lot of the gain that we saw … it was kind of false gain. Or maybe the quality was not as good,” Giarrusso says.

So he says getting a detailed picture of what’s happening on the ground can determine how a city’s trees are faring and the effects on people nearby.

Reporting credit: Sarah Kennedy/ChavoBart Digital Media