The wording actually says "increased yields," not "doubled." I farmed nodes of various types earlier today on a low-level alt and was definitely getting increased yields, but I don't know whether they were doubled.
Surveys are never doubled, because I guess that would be abused.
Extras like heartwood, bast, viridian dust, and even worms do not appear to be doubled, either-- although I did get a few nodes where the bast or heartwood was doubled, but most nodes had only 1 (if any) of those.