I'm looking at recipes, and it seems wood is needed to make natural fiber etc, eventually being used to make advanced roboports which require 10 wood each and reactors which require 150. Yet, I also see no way of getting wood aside from destroying trees. Are these buildings intended to be very limited in how many you can build?

To the best of my understanding, yes. And I agree, it's a very odd decision. Iron ore, copper ore, stone? You can get "infinite" amounts of those by stage 2. Wood and coal? That's end-game stuff.

But you also don't need all that much wood, and not perpetually for science. Nuclear reactors generally happen after bots, and once you have bots, 5k wood is pretty easy to grab.