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.

Great Research Study, Great Results!

It's always tempting to focus on the extremely fast growth of many tree species in tree tubes.  It's hard not to focus on it when you see crabapple trees start the year as six inch seedlings and emerge from 4 and 5 foot treeshelters before the end of summer!

But it's important to remember that fast growth in tree tubes is really just a means to an end - and that end is simply the long term survival of the tree.

All too many tree planting projects end in failure due to low seedling survival.  Deer browse, competing vegetation, drought, wind and moisture stress and other factors all play a part.  For most tree planters the bottom line is survival, which simply means: not having to plant that same piece of ground again.  Fast growth is nice, and it's something to brag about to your neighbors and friends, but the main thing is simply success.

That's why this article is so great (follow the link and then click View Document).  This studied tracked survival rates of four species, baldcypress (yes! baldcypress grows great in tree tubes!), water tupelo, swamp blackgum and green ash over five years, in 4 different types of sites and in the face of severe herbivory from beavers.  Some interesting results:

Baldcypress, planted in a willow area,
With tree shelters: 97% survival
Without tree shelters: 45% survival

Green ash, planted in a grassy area,
With tree shelters: 90% survival
Without tree shelters: 8% survival

Green ash, planted in a a willow area,

With tree shelters: 88% survival
Without tree shelters: 2% survival

No, not all of the results were this dramatic, and I'm "cherry picking" the most compelling results the way that all salesmen tend to do. 

But almost across the board the results tell one story:  Success (with tree tubes) versus Replant (without tree tubes).