A customer asked a very good and well informed question this morning (that's not surprising - our customers are the smartest and best informed tree planters out there!): She had read that trees need to shake and sway in the wind in order to add stem thickness/caliper, and worried that this would not happen in tree tubes.
I gave a three part answer, which this poor customer probably regarded as "20 minutes of her life she'll her life she'll never get back," even though she was kind enough to listen and sound appreciative. To save you the same 20 minute discussion, here's the Reader's Digest condensed version:
1) It's true that while a seedling is growing up through a tree tube and out the top it does not sway or flex as much as an un-tubed tree, and has a thinner stem relative to its height than the un-tubed tree. (On the plus side, the tree is the tree tube is actually alive after the first few years, whereas odds are increasingly against the same being said for the un-tubed tree, due to deer browse and drought.)
2) This is not as true for the new vented Tubex Combitube Tree Tubes we offer here at Wilson Forestry Supply, especially when that vented tree tube is coupled with a PVC stake. Vented tubes have been shown to promote better stem diameter growth than the old, unvented treeshelters used years ago. And using a PVC stake allows the tree tube - and therefore the tree inside - to sway in the wind, triggering the same growth responses you see in an un-tubed tree: increased stem caliper and taper.
3) Even with today's better tree tubes and with PVC stakes, at the point in time the tree emerges from the tree tube it will have a thinner stem relative to its height than would an un-tubed tree. That's OK! That's why our tree tubes are designed to last 5+ years, so that after the tree emerges the tube can continue to support the trunk. Once the emergent tree starts swaying in the wind you will see that it quickly adds stem taper and thickness.