It’s much more comfortable and enticing to get outdoors and walk to work or to the store if you’re walking under a canopy of street trees. The tree canopy not only shades you from the sun, but the trees themselves transpire, which means that they emit moisture into the air, keeping you even cooler. They also clean stale air, replenishing it with oxygen. Trees are also more interesting than just a barren sidewalk, and street trees on your street (especially if one is in front of your house) raise the value of your house.