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Independent Studies

THE SITUATION

Every year people who plant trees install millions of tree protectors. The people who make such purchases often do so after listening to manufacturer claims and little else. While many of these claims are supposedly backed up by data, the data are often presented in a biased or incomplete way.

Nonetheless, it is true that trees with protectors are better off in the vast majority of cases than trees without any protection. It is not true that all protectors and shelters provide equal protection.

As a result of the lack of good, unbiased data, most tree planters are oblivious of the harm being done to their trees. Moreover, in many cases those who do the actual plantings do not return to the site to inspect the trees and are therefore not aware of the harm these protectors do.

 

BACKGROUND

The good that protectors do has been well established. Many studies (not included here) and countless applications attest to their success in protecting trees from animals, stimulating growth, etc.

The problem arises from the fact that not all protectors perform these functions equally well. Some actually harm, even kill the trees they're supposed to protect.

 

PROTECTOR FUNCTIONS

Primary functions are to promote tree health and improve survival. Secondary functions have to do with the growth rate of the tree.

 

HEALTH & SURVIVAL

Deer, mice, voles, and other critters damage and destroy millions of newly planted trees each year. Although many of these trees may cost less than a quarter apiece, the labor and overhead costs can be much higher. The cost of replacing dead trees is higher yet.

According to a study conducted by David Wise of the Chesapeake Bay Foundation, data from 29 CREP sites showed almost four times as many trees protected by Tubex shelters died from vole infestation as did among trees protected by Tree Pro protectors. The actual mortality rate was:  21.4% for Tubex vs. 5.1% for Tree Pro.

Malcolm Olson of Olsen's Tree Farm in northwestern Pennsylvania and southwestern New York found only one solitary mouse in the 80 Miracle Tube shelters he installed. In the other shelters he used, he found that between 50 and 60% were infested with mice, most with families of mice.

It is believed that the higher incidence of rodent infestation has to do with the cozier environment provided by some protectors. Unvented protectors that are pressed down into the ground are the worst offenders in this regard because they provide rodents with a warmer environment.

Tree health and survival have to do with more than protecting the trees from animals. As is shown below, protectors can create an environment that places tree health and survival at risk.

 

GROWTH RATE

It's well-known that tree protectors accelerate growth.

Dan Myer of the Department of Forestry, University of Wisconsin, reported that, "Tree shelters have increased growth in some oak trials in England by as much as 500 percent in three growing seasons; 350 percent is not unusual.  Most U.S. trials report 100 to 200 percent improvement over unsheltered seedlings."

Unfortunately, this growth is vertical only. Although a more rapid vertical growth rate is generally a good thing, there is a downside if the rate is excessive. Rapid vertical growth, without commensurate diameter growth, produces a stem that is sometimes too thin to support the canopy. This sometimes causes the top of the tree to snap off even in moderate winds.

While all protectors stimulate vertical growth, excessive vertical growth is a primarily a problem of the darker unvented shelters. Because they transmit less light, the tree will "concentrate" growth on the vertical in an effort to reach the light entering the top of the shelter.

With lighter colored vented shelters such as Tree Pro and Miracle Tube, enough light enters the protector wall to stimulate diameter growth.

During a study lasting from 1996 to 2002, Purdue University of West Lafayette, Indiana, found the shelter with the lightest color; i.e., Tree Pro, produced a 35 percent improvement in diameter growth in Engelmann spruce seedlings over the shelter with the darkest color; i.e., Tubex.

According to Dr. Hailu Sharew of the Maryland Department of Natural Resources, seedlings protected by Tubex brown protectors attained a height of 53.7 inches and a diameter of .462 inches after three growing seasons. The average Tree Pro seedling attained a height of 65.5 inches and a diameter of .646 inches.

The average Miracle Tube seedling did even better, the best of the five protectors studied. (Tree Pro was second best.) The average Miracle Tube seedling attained a height of over 74 inches and a diameter of .678 inches in that same period of time.

The diameters of trees in Tree Pros outgrew trees in Tubex by more than 37 percent.

The diameters of trees in Miracle Tubes outgrew trees in Tubex by more than 47 percent.

Paul Easley, 1990 Illinois Tree Farmer of the Year, wrote that, "We stuck [Tree Pro] tubes over a couple of acorns as they sprouted out of the ground and, to my amazement, they outgrew some of the nursery stock."

Jim Hissom of the Pennsylvania Forest Stewardship Program said that thanks to 48 and 60-inch Miracle Tube shelters, "The growth [of 16 American Chestnuts and 20 black cherry cultivars] was phenomenal, despite the unusual amount of rain."

 

PROTECTOR FEATURES & CHARACTERISTICS

Features are attributes that are intentionally designed into the protector. Characteristics, at least in this use of the term, include unintended consequences of a given protector design. Since it's sometimes impossible to separate the two, at least without having first-hand knowledge of the intentions of the designers of other protectors, we lump these two together.

For the purposes of this discussion, all attributes fall under the following categories:

 

  • The Greenhouse Effect
  • Interior Temperature
  • Translucence
  • Material
  • Size
  • Color
  • Portability
  • Durability
  • Tree Maintenance
  • Installation
  • Removal & Disposal

GREENHOUSE EFFECT

Tree protectors and shelters create a "mini-greenhouse" inside the tube. Both temperature and humidity are generally higher on the inside than on the outside.

For years, many of us in the industry believed this was beneficial to the tree. Under ideal circumstances, it is. However, conditions are seldom ideal. Under real-world conditions, some tree shelters cause heat to increase inside the protector to such an extent that the tree is harmed and sometimes even destroyed.

A "closed" system; i.e., one in which the only air circulating into the protector is through the opening at the top, is not healthy for the tree. In order for photosynthesis to take place at the optimal rate, there must be a ready supply of fresh air. A closed system also promotes the retention of excessive heat and moisture inside the protector.

In late winter and early spring, some of these protectors; e.g., the darker, unvented type, cause the trees to emerge from dormancy. In direct sunlight over a period of days, even in January, it can get warm enough inside the shelters for the trees to come out of dormancy prematurely. That often results in death and dieback when the temperature drops again.

The reverse happens in the fall when the trees are supposed to go dormant. Instead, some protectors (again, the non-vented kind with darker, less translucent colors) retain heat, which delays the trees from going dormant.

As a result, when the outside temperature drops into the low 20s, dieback and worse often occur because the trees haven't yet gone dormant.

 

TREE PRO & MIRACLE TUBE

TREE PRO (the company) manufactures two different tree protection tubes. One is Tree Pro tree protectors. The other is Miracle Tube tree shelters.

Tree Pro protectors are furnished flat and are formed into tubes when they are installed around the trees. Miracle Tube shelters are solid tubes that are furnished in nested groups of five units, one inside another of a slightly larger diameter.

Both Tree Pro and Miracle Tube designs eliminate the Greenshouse Effect's detrimental impact while retaining its benefits. They have just the right color (hue and value) to prevent the absorption and retention of excessive heat. They have exactly the right amount of translucency to admit the proper amount of light.

In addition, the right number and size of holes have been drilled into the sides of these protectors. This allows the right amount of fresh air to circulate through the protector.

Note: For those applications where the Greenhouse Effect does not produce detrimental effects; e.g., mild summers and winters, both Tree Pro and Miracle Tube can be supplied without holes.

 

UNVENTED TUBES

With unvented tubes, the only way that excessive heat build-up can be dissipated is by lifting them. This labor-intensive exercise requires each lock-tie to be loosened, which after a couple years can cause some of them to break. Worse, if the shelter was pressed down into the ground when it was installed, it must now be twisted back and forth to break loose from the soil compacted around it. When temperatures stabilize, the tube must then be lowered, then raised again to accommodate the change in seasons. 

It should be noted that lifting shelters may not necessarily solve the problem. In certain hot, dry conditions, lifting the shelter produces a "chimney effect," which can cause the leaves to become dessicated. 

 

INTERIOR TEMPERATURE

During the summer, the temperature inside some tree protectors can be more than 30 degrees Fahrenheit higher than ambient temperatures. At that temperature, the trees' leaves turn black and fall off. The trees suffer dieback, lose their disease-resistance and sometimes even die. 

Some tree protectors are worse than others. To overcome this tendency to "trap" heat, both Tree Pro and Miracle Tube are light in color (thereby absorbing less heat) and if specified, can be furnished with ventilation holes to improve the dissipation of heat.

According to research conducted at Pennsylvania State University Forestry Department, [1] "Maximum daily temperatures inside the unventilated brown plastic [Tubex] shelters were consistently 25 to 30 degrees Fahrenheit higher than ambient temperatures.

"The maximum unventilated tree shelter temperature recorded at the site [i.e., inside Tubex tree shelters] was 126 degrees F."

These extreme temperatures are due to the increased absorption and trapping of warm air inside the shelter.

 

TRANSLUCENCE

Translucence refers to the amount of diffused sunlight transmitted through the protector wall and is a function of the opacity and color of the material used. Clear material transmits most of the light while dark-colored opaque material transmits very little.

Anecdotal evidence, trial and error experience, as well as some studies have generally arrived at a consensus that the ideal protector transmits between about 25 and 50 percent of the available light. This mimics the natural habitat in which a seed germinates beneath a forest's canopy.

According to Dr. Hailu Sharew of the Maryland Department of Natural Resources, [2] both Tree Pro and Miracle Tube protectors transmitted significantly more light than both Tubex green and brown shelters. Percent Photosynthetic Flux (PPF) transmission through the protector wall was 12 percent for Tubex brown, 16 percent for Tubex green, 30 percent for Tree Pro and 34 percent for Miracle Tube.

 

MATERIAL

Protectors and shelters are made of materials that are supposed to photodegrade within about five years. That's so they'll break down and become too weak to interfere with continued tree growth; i.e., they won't girdle or strangle the tree. On the other hand, protectors that last less than this length of time aren't doing their jobs.

UV inhibitors are added to the protector material to make sure the protectors last for the prescribed length of time. Unfortunately, some manufacturers add too little to their products and others add too much.

 

SIZE

We won't go so far as to say that bigger is better; however, there is strong evidence that shelters smaller than 3 1/2 inches in diameter are too small and can negatively affect the growth and health of trees. The leaves get bunched up inside the shelter so badly that the trees stop growing. The trees again lose disease-resistance and become vulnerable to all sorts of woodland organisms.

Tree Pro diameter is 3 1/2 inches. Miracle Tube diameters range from 3 1/2 inches to 4 3/4 inches. These diameters are well above the size necessary to promote good growth and avoid dieback and disease. 

And if that's not enough for your application, Tree Pro also offers the Tree Pro SuperWide at 4 1/2 inches in diameter and the DoubleWide at a whopping 7 inches in diameter! 

 

COLOR

The color spectrum of sunlight is modified as the light passes through the protector wall. At a very basic level, two aspects of color (hue and value) are important: One is the extent to which a given color modifies natural light. The second is the degree to which a given color absorbs heat from the sun.

Darker colors absorb more heat than lighter colors and therefore can cause excessive heat to accumulate inside the protector, thereby damaging or destroying the tree. More intense colors cause a greater change in the natural light spectrum and can therefore disrupt photosynthesis to a degree that affects tree health and growth. [Author's note: More studies need to be done to establish optimal light transmission properties.]

Both Tree Pro and Miracle Tube are made of a light beige polyethylene. Heat build-up and retention are negligible as is the distortion of natural light frequencies.

 

DURABILITY

Most shelters, including Miracle Tube, Tree Pro and Tubex, have proven they're durable enough to provide protection until the tree has reached a size adequate to stand on its own. Only one protector, called "Tree Pee," was evaluated as unusable by the MTDC Materials Durability Study [3].

 

TREE MAINTENANCE

There are times when it is advisable to remove or open the protector to perform maintenance on the tree; e.g., pruning, removal of suckers, debris, animals, etc. This is especially true of high-value tree species and varieties. Closed-design  protectors (solid tubes) are unsuitable for these applications. Tree Pro protectors, which are of the open design, are ideal for maintaining trees. 

According to the American Chestnut Cooperative, Tree Pro is the best-designed tree shelter. "In addition to Tree Pro, we've used Tubex and Tree House shelters. Tree Pro is the easiest to install. It's the easiest to open to check seedling progress and the easiest to open in the fall to allow the seedling to harden off." [4]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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