Personally i think the availability of tower-cap wood is a bit too stifling for it to be used so abundantly in dwarf goods/manufacture. There should be some way to control and help them grow faster/more reliably, especially in more efficient places. The same could go for aboveground trees of course.
So i had the idea of being able to uproot saplings and plant them where you want them to grow, in tree nurseries or orchards or tree gardens or something. You would need a free bag to keep the roots and some dirt in, and you could sell the whole thing as a trade good instead (surely elves wouldn't object to purchasing live trees right? Watch out for the leather bags you have them in though.) and more importantly import these saplings.
Once the saplings are placed in the tree nursery you get the bag back and the saplings will continue to grow as normal, maybe with the option to fertilize them to minimize the chance of them dying and maybe speeding up their growth. Once fully grown, the trees can't be moved in this way and can be chopped down at leisure or allowed to reproduce saplings in the surrounding tiles (maybe including nursery tiles?) which you can individually dig up and replant wherever you want them. Certain problems could be avoided if 'plant sapling' was treaded as a one square building placement instead of a multi-square nursery plot which is no longer a building once placed (like constructions) Or make them work like roads (and constructions in the next version), having to place one sapling per square or something. Would only be viable for small squares or lines, but you don't want a solid square of trees anyways.
This ability would allow wood production to be safely kept away behind your walls. It would also allow hippy aspiring dwarves to make a wall of trees to keep non-firemaking enemies out. These orchards would also come in real handy if/when you can start getting fruit and other non damaging products from trees. Like the elven way of getting wood without killing a tree, feather tree fibers for cloth and stuff, or rubber from rubber trees. Obviously the elf way of getting wood without killing the tree should be a secret kept very closely by elves.