Outstanding stem caliper growth in 2nd year oak planted as
an 18 inch seedling in a 4ft Tubex Combitube Plus Tree Tube.
I divide the history of Tree Tubes in the USA into two distinct eras: Before Venting (B.V.) and After Venting (A.V.). Venting - the seemingly simple act of punching holes in the solid walls of the tree tubes - is the single most important advancement in the development of tree tubes.
By 1989 treeshelters were widely used and accepted in the UK. The largest and best maker of treeshelters was Tubex, Ltd. Tubex Treeshelters were introduced to the USA in 1989 by a small company based in St. Paul, Minnesota.
At that time all tree tubes were unvented - solid translucent corrugated tubes. It was thought at the time that the rapid growth of tree seedlings inside the tree tubes was due to the creation of a "greenhouse effect," and the goal was to create an air-tight growth chamber.
I was there at the beginning. I was the first employee - fresh out of forestry school - of that first company that introduced Tubex Treeshelters to the USA. By and large the results in the field with those unvented tubes were good - excellent survival rates, rapid height growth, and of course "not getting eaten by deer" generally beats the heck out of "getting eaten by deer."
But we also started to get some troubling reports of problems from the field - and not coincidentally those problems were more serious the farther you got away from areas with climates most similar to the UK. Those unvented tubes performed well in the Chesapeake Watershed region, and in coastal California and the Pacific Northwest.
However, get the farther north or south you went, the more frequent and serious the complaints. These complaints fell into three categories:
1) Winter injury. In northern climates seedlings in tree tubes simply didn't harden off properly for winter, and often suffered die back due to cold weather.
2) Spindly stems. Seedlings in tree tubes exhibited rapid height growth, but the trees had very thin stems relative to the height of the trees.
3) Fungal problems, notably in the south, and probably due to excess moisture in the tree tubes.
So by this point - and we're talking about the mid 1990s - the potential of tree tubes to increase survival, shield valuable seedlings from deer browse and accelerate height growth was clear to all. However, it was equally clear that in many cases, and especially the more extreme the climate, the upside of using tree tubes was largely counteracted by the side effects: winter injury, thin stemmed growth, and fungal diseases.
Enter some good ol' Yankee ingenuity! Every software package ever introduced has had 'bugs' that needed to be ironed out with subsequent updates. The first effort at 'de-bugging' tree tubes was a partial recognition that air flow in the tubes can be good; growers in northern climates were advised to elevate their tree tubes in early autumn to allow the trees inside the harden off for winter, and then lower the tubes back to the ground after the first hard frost.
This advice worked as far as it went; elevating the tubes did greatly reduce the incidence of winter injury. It also exposed the base of each seedling to rodent damage at a time of year when rodents are hungrily feeding in preparation for winter.
Then some enterprising landowners applied something that we tree tube peddlers sorely lacked: Common sense.
Landowners started drilling holes in the tubes, and then calling to tell us how well their trees were growing. And we tree tube peddlers did what most 'experts' do: We ignored them. In was only when research done in far away France confirmed - and scientifically explained (more about this below) - the benefits of venting that we finally took notice... and slapped ourselves on the forehead with a loud "d'oh!"
The performance of vented versus unvented tree tubes is night and day. Venting didn't just solve the side effects of those early tubes. It unleashed the full potential of tree tubes to massively increase total biomass growth.
The French researchers figured out that in solid tubes carbon dioxide often becomes a limiting factor - the seedling uses all of the CO2 in the tube then grows very little until the CO2 level recharges. In vented tubes the CO2 level is constantly recharged, and never is a limiting factor.
In addition properly vented tubes (such as the Tubex Combitube Plus) allow dappled sunlight to strike the leaves, and allow a puff of air to gently shake the leaves. In both cases this triggers growth responses in the tree similar to if the tree was growing in full sun in an open field (namely thicker stem caliper growth and better root development) - except that the seedling still enjoys complete deer browse protection and a massive reduction in moisture stress a compared to its un-tubed comrades.
Even though unvented tubes performed well in areas with mild or maritime climates, it is important to understand that there is no climate in which an unvented tube outperforms a vented tube.
So you can see why I divide the history of tree tubes in American into B.V. and A.V:
Before Venting:
Complete deer browse protection
Increased survival
Rapid height growth
* Winter injury in cold climates
* Thin-stemmed growth in all climates
* Fungal diseases in hot/humid climates
After Venting:
Complete deer browse protection
Increased survival
Increased total biomass growth - height, stem caliper and roots
No more winter injury
No more fungal disease issue
In summary, tree tubes as they were developed in the UK were a great idea, but it took some French research and bunch of landowners with cordless drills and common sense, to unleash their full potential!
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