Happy oak in a Wilson Tree Tube

(Click to enlarge)

Last week at this time this little bur oak seedling was happy to be safe inside this Tree Tube, rather than exposed to 30 to 40mph wind gusts that would have dried it out.

Today the seedling is just as happy not to be exposed to a blistering sun - it's over 90 degrees here in Minnesota. 

I'll be photographing this bur oak every Monday, to put together a time lapse sequence as the growing season goes on.  This is a really fun thing to do, in part because it's always fun to see how fast your trees are growing in their tree tubes (some guys supercharge their cars to see how fast they can go, I supercharge my trees to see how fast they'll grow!), and in part because making a weekly visit to your trees really makes you appreciate how stressful growing conditions are for unsheltered trees, and how much tree tubes function to reduce stress.

Stress is to tree growth what friction is to motion.  Low stress = Fast growth!

Tree Tubes spell relief from wind & moisture stress

(Click to enlarge)

Looking at this photo you can practically hear the little bur oak seedling sighing, "Ahhhh."  I took this photo yesterday.  Nice sunny day, but the wind was howling with gusts up to 35mph and more.

 

An un-tubed bur oak seedling - or any seedling - would have been under severe moisture stress as the wind continually stripped away the moist envelope of air surrounding the leaves. Not this guy.  All he "felt" was the gentle swaying of the tree tube thanks to its PVC tree tube stake.  No wind.  No stress.  Just perfect conditions for growth. 

Why do trees grow so much faster in tree tubes?  Two reasons (well it's a lot more than two reasons, but we'll concentrate on two for today).  One a windy day like yesterday the leaves on un-tubed trees close their stomata - the pores through which they exchange gases and transpire moisture.  This is a good strategy for conserving limited moisture resources, but it's a bad strategy for photosynthesis, which slows dramatically.  In other words, it's a survival strategy, not a growth strategy.  By contrast the leaves of a seedling in a tree tube keep their stomata open and photosynthesis continues full bore.

Since the leaves of the seedling in a tree tube are not exposed to stressful, windy conditions they can optimize their morphology and structure for growth:  High surface to weight ratio to optimize light absorption and gas exchange, bright glossy surface.  The leaves of a seedling outside a tree tube are smaller, thicker, darker and duller.  They are survival leaves, not growth leaves.

To put it another way (and to use a Memorial Weekend analogy), the leaves in a tree tube are an Indy car, while the leaves of an un-tubed seedling are a 1974 Pinto.