And here's two attempts at vines:

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This is basically a layer of green with a bunch of layer effects (bevel and emboss, drop shadow) and a layer mask. Then I drew in a bunch of squiggles with a one-pixel brush on the layer mask. I can't decide which blend mode I like best -- normal or color. The latter feels like a more natural part of the scene, but it's also considerably more subtle.

Either way, doing the whole city is going to take aaaaages.