I'm not sure if the goal of "restoring New York to what it once was" can ever be physically perceptible, but the virtual restoration on themannahattaproject.org is fascinating. There is something very small and poetic about reintroducing native plant species to an environment like New York, and something very elegiac about seeing the same seasonal changes that were once happening on the island 400 years ago. For an introduction to the project, see the Restoring Mannahatta article in the Home and Garden section of the New York Times.
