This isn't universally true, especially in climates where trees grow naturally. Oftentimes, the poorest neighborhoods in a city are among the oldest, and thus the trees have had the most times to mature and grow.
For example, look at
<a href="https://maps.google.com/maps?ll=40.684543,-73.948116&spn.... Bedford-Stuyvesant is one of the oldest neighborhoods, and was once wealthy. Now it is one of the poorest neighborhoods in inner Brooklyn, but the trees have grown large with age, and that makes it one of the greenest neighborhoods from above. Vacant lots even grow verdant with age.
Bed-Stuy is also one of the neighborhoods currently going through the most gentrification in NYC. Other tree-lined, brownstone neighborhoods, closer to Manhattan may have been first (Fort Greene, Park Slope, Clinton Hill, etc), but Bed-Stuy is the place currently dealing with it.
Sure, neighborhoods that don't have trees and brownstones get targeted -- look at what happened to Williamsburg -- but that's largely due to proximity to the city. Trees get planted after the fact in this case.
If Bed-Stuy wasn't beautiful, it'd be a lot harder of a sell for the gentrifiers.
Bushwick and Williamsburg don't have particularly beautiful architecture-- just lots of vinyl-sided wood frame tenements. Williamsburg is already as expensive as parts of Manhattan while Bushwick is gentrifying rapidly too. Just about all of Brooklyn within close range of Manhattan is either already very expensive or moving in that direction.
For example, look at <a href="https://maps.google.com/maps?ll=40.684543,-73.948116&spn.... Bedford-Stuyvesant is one of the oldest neighborhoods, and was once wealthy. Now it is one of the poorest neighborhoods in inner Brooklyn, but the trees have grown large with age, and that makes it one of the greenest neighborhoods from above. Vacant lots even grow verdant with age.