Last weekend, the air in New York was decidedly crisper than the weekend before. There were more leaves on the sidewalk, and the rain didn't feel so much like it was watering the city's plant life -- as it does throughout the spring and summer -- and more like it was practicing for when it will metamorphosize into snow.

It's fall, and with fall, we're often inspired to think about nature again. We have to recapitulate our relationship with the elements -- we don heavier coats and start wearing sweaters again, we start eating differently, and we might start paying more attention to the few nice days we have left before winter.

Such was the case for me last weekend, during two long runs in Central and Prospect Parks. I relished the cool air and the smell of autumn rain. It not only helped my running; it made me appreciate trees.

But please, I'm not a hippie, I don't have a yoga mat rolled up in the corner, and I don't talk about nature as a force. I'm a bit too cynical for all that.

Nevertheless, these runs reminded me of how central trees are to our well-being, especially those of us who live in urban environments, where trees can be hard to find.

So when I came upon a group of workers from the MillionTreesNYC initiative being sponsored by American Express last week, I had to take a moment to learn more about it.

MillionTreesNYC plans to increase New York City's tree population by 20 percent over the next 10 years. This means one million trees by 2018 -- hence the project's name.

It's a massive undertaking, but very much in line with the city's increasingly "green" agenda. Indeed, the New York Times magazine this weekend was devoted to green issues, and the most recent MTA ads tout the organization's dedication to eco-friendly transportation dating back to 1960.

To learn more about MillionTreesNYC, click here. When you're done with that, I might suggest heading to your local park.

[Image: Jdforrester]