I'm talking about the ones in the picture. They're quite large but have almost no exposed dirt above them. So they're relying on roots to ground water. Trees that size struggle in Boston. See the larger trees that regularly fail on beacon Hill or the ones that die regularly in city hall plaza.

Boston actually waters new trees, but not nearly enough. We had a new tree put in out front mid summer. I watered it regularly in addition to Boston's contractor watering it every week or two and managed to get it to survive the dry as hell summer we had. The gallon of dog urine that it gets doused with daily doesn't help things either.