329 W. 21ST STREET

When we purchased our small co-op apartment in Chelsea more than 20 years ago, the biggest appeal to us was the deck and garden area that came with it. Hidden behind the main 10-unit building, the dominant feature of the small courtyard was a large, old ailanthus tree. It attracted rare and unusual birds, resting on their migratory paths. It gave us shade in the summer and leaves to sweep in the fall. Its only downside, we thought, was that we had to scoot around its massive, elephantine trunk when bringing food from the building to our outside dining table.

For 20 years, we enjoyed our tree. Then, one day last winter, we noticed something peculiar: The tree's roots were breaking through the ground, coming up and pulling our wooden deck up with them.

When I bought a one-bedroom co-op in Chelsea in 1994, I could feel the doors of affordability close right behind me. Just a year later, my apartment would have sold for twice as much, which would've been way out of my modest price range. Today, it's worth seven or even eight times what I paid. Like a lot of folks who rode the Chelsea real estate wave, I feel like I won the lottery.

But there's a serious downside to all this "wealth" creation, and that is when your longtime neighbor cashes out for retirement in Florida or Panama, and the new buyers — who are genuinely wealthy — begin to move in.