It is general wisdom that you redraw the entire viewport on each frame.

I would like to use partial updates; what are the various ways can do that, and what are their pros, cons and relative performance?

(Using textures, FBOs, the accumulator buffer, any kind of scissors that can affect swapbuffers etc?)

A scenario: a scene with a fair few thousand visible trees; although the textures are mipmapped and they are drawn via VBOs roughly front-to-back with so on, its still a lot of polys. Would streaming a single screen-sized texture be better than throwing them at the screen every frame? You'd have to redraw and recapture them only on camera movement or as often as your wind model updates or whatever, which need not be every frame.