I love learning new botanical and plant physiology terms and understanding how they apply to the science of tree tubes. I have written several posts lately about how today's tree tubes produce saplings that resemble open-grown trees in terms of stem thickness and stem taper, as compared to trees grown in the old, small diameter, unvented tree tubes we used years ago (and, of course, as compared to open-grown trees that get eaten by deer, killed by drought or swarmed under by weeds!).
Three advancements in tree tube design help account for this.
1) Larger diameter tubes - leaves in today's larger tree tubes are able to fully expand and absorb more light; they "think" they are open grown as opposed to compressed in a small diameter tree tube.
2) Vented tree tubes - venting has several advantages, including increased CO2 availability and allowing the tree inside to go dormant for winter to avoid frost damage. Another advantage is that the air flow through the tubes gently shakes the leaves, "telling" them they are growing in an open field while still giving them the protection and moisture stress reduction of a tree tube.
3) Flexible PVC tree tube stakes - our pvc stakes for tree tubes sway in the wind, and that shaking triggers the production of ethylene, which in turn tells the tree to allocate more of its growth resources to stem thickness and taper.
In researching these posts and looking for a way to explain this phenomenon I came across the term "seismo stress." I probably learned that term back in plant physiology in forestry school, but since that was a long time ago (before the evolution of angiosperms), I had forgotten it. In fact I probably forgot it the day after the exam. If not before.
Seismo of course refers to shaking, in the way that a seismograph measures the amplitude of earthquakes. Too much shaking induces stress that inhibits growth. A little bit of shaking (e.g. with a vented tree tube and a pvc stake) encourages a better balance between height growth and stem diameter.