Forest Finance Tree Shelters: A Multipurpose Forest Management 7 Tool Due to the heavy deer browse in many Post-shelter Stability and Growth Introduction parts of Pennsylvania, some form of Often seedlings are not able to stand seedling protection is almost a necessi- upright as they come out of the “Tree shelter” is a generic name for ty. Other tools to protect seedlings in- unvented shelters. Some research a solid (or mesh) tube that is placed clude repellents and fences. Repellents indicates that vented shelters show the over a seedling to provide favorable are not reliable, except in small areas same diameter growth as unsheltered environmental conditions for seed- and over short periods of time. Cost seedlings. Furthermore, research ling growth. During the early 1980s, of repellent materials and labor for indicates that unsheltered trees do tree shelters were introduced in repeated applications are often prohib- as well as sheltered seedlings a few Pennsylvania primarily to improve the itively high. Deer fencing, discussed in years after emerging from the shelter. survival and growth of newly planted Forest Finance 2, is an economical al- For eastern hardwoods, the seedlings trees. Tree shelters were originally de- ternative in many situations, especially usually take about two to three signed to create a “greenhouse”-type for larger regeneration areas. growing seasons to emerge from the environment by increasing air tem- shelter, but need an additional 2 to 4 perature, humidity, and carbon diox- Tree shelters play an important role years’ support to enable the trees to ide levels. in many situations. this publication strengthen and support themselves. discusses uses, types, and costs of tree Fast-growing trees may require early At first, shelters received much atten- shelters. shelter removal. Alternatively, some tion and were heavily used, but recent shelters have slits that can be opened usage has slowed due to the forestry so that the shelters may be left in community’s concerns about expense Pros and Cons of Tree place after seedlings emerge. Most and success. Over the years, tree shel- Shelters manufacturers recommend leaving the ters have been redesigned a number Early Growth shelter in place until the tree reaches of times. Results differ as new shelters Many studies indicate that in the the diameter of the tube. Once out arrive on the market. early stages of development shelters of the shelter, some species adapt produce seedlings with longer stems well to differing environmental and The reported benefits of tree shelters and fewer branches, but they are competing vegetation conditions and include reduced stresses on seedling smaller in diameter compared to can develop into forest-grown trees. growth and protection from animal unsheltered seedlings. The shade Widely spaced trees may develop damage. Government agencies, pri- acclimation and light reduction— heavily branched crowns rather than vate forest landowners, and farmers along with less wind and fewer vertically growing stems characteristic in Pennsylvania use tree shelters mechanical stresses—allow sheltered of commercial timber trees. to establish trees on old field sites, seedlings to concentrate most of their along streams, and in natural forests. energy on height growth, not on roots Deer Much of the research on shelters in or stem diameter. Research has shown Pennsylvania focuses on the highly Most foresters use tree shelters to pro- that sheltered seedlings’ height growth valuable commercial timber species tect against deer browse. Tree shelters, was almost twice that of unsheltered such as northern red oak (Quercus if tall enough, are usually successful seedlings in the early growing years. rubra) and black walnut (Juglans nig- at protecting seedlings from deer and Height growth will reportedly slow ra). Using shelters around these and other mammalian browse. A 4-foot if the shelter is not well sealed to the other valuable hardwoods in old fields shelter is most common and is said to ground. mimics natural regeneration under prevent most deer browsing. However, shade by lowering light intensities, 5-foot shelters are recommended in increasing humidity, and reducing air deep snow or in areas with severe deer movement. Reforesting riparian areas browse. In addition, deer may eat un- is extremely important for restoring desirable seedlings that are present in water quality and providing other the understory, reducing weeds (com- economic and environmental benefits. petition for the protected seedlings) Shelters are also used on extreme sites and possibly costs associated with the (e.g., reclaimed surface mines) and need to spray unwanted vegetation. areas where seed sources are absent. Bucks may rub against shelters; there-

2 fore shelters need to be securely staked Competing Vegetation Temperature to the ground. In addition, shelters Using tree shelters may not eliminate The high temperatures reached will protect seedlings from bucks rub- the need to control competing in shelters can rise above the bing their antlers on newly established vegetation. Weeds in shelters are optimal growth range of some trees. generally not a major problem, but species. Although touted to provide weeds and grasses surrounding shelters greenhouse conditions, some research Rodents have been shown to decrease seedling has shown that ventilation or use of If well secured to the ground, shelters growth and reduce the shelters’ mesh shelters causes less mortality can prevent small animals such as effectiveness. Roots of sheltered by allowing heat and humidity to rabbits, voles, and mice from girdling trees are smaller in comparison to dissipate. Ventilated shelters, on the the seedlings. However, shelters are its stem (smaller root-to-shoot ratio other hand, reduce the greenhouse also known to harbor rodents that than normal trees) and therefore effect—the beneficial microclimate— seek protection from predators. need to fight harder with competing and may make seedlings more Thick vegetation around shelters vegetation for water and nutrients. favorable to insect attack. Wet and provides excellent rodent habitat. Competing vegetation is often more humid conditions due to higher Research has shown that lighter adapted to a site and is more vigorous temperatures have also been shown to and brighter shelters have less vole and aggressive than the desired cause mold in unvented shelters. damage than dark ones. To minimize seedling. If competing vegetation rodent damage, install the shelter control is necessary, shelters will help Unvented shelters have been known snugly to the ground but not in the protect the seedlings from herbicide to cause dieback or mortality due to ground. Check the inside of shelters application. higher maximum temperatures and periodically for damage or rodent lower minimum temperatures (in win- nests. Remove any nests that you ter). This has been attributed to insuf- Wind find. Bait such as a rodenticide placed ficient “hardening off” of the seedling. inside or around the shelter at regular Wind protection provides reduced Some shelters are designed to slide spacing can be used as a control. transpiration by increasing the relative off or open to reduce this problem. humidity inside the shelters. Although Shelters may also cause seedlings to important to facilitating seedling break bud earlier in the spring, mak- Birds and Insects growth, wind can knock over shelters, ing them susceptible to late frosts. Birds, especially songbirds, are a killing the trees. Stake and support nuisance because they perch on the placement is important­—shelters Natural Regeneration shelters and can damage emerging begin to lean if not well secured. Tree In order to protect natural shoots and inhibit terminal growth of shelters must be inspected periodically regeneration, judiciously select the trees as the shoots reach the tops to ensure that they are straight and potential “crop” tree seedlings that of the shelters. Mesh netting placed secure. look healthy and place shelters over over the shelters prevents birds from them. Tree shelters can also be placed falling into the shelters and dying. over stump sprouts in harvested Plastic Waste Netting also reduces wasp and bee stands. Shelters’ best results come in Many shelter manufacturers claim nests as well as damage from Japanese full- or near-full-sunlight conditions. that their products photodegrade. beetles. Bears may destroy tree Light levels are critical since shaded Regardless of how long the shelters shelters while in search of bee nests seedlings grow slower and often fail to last, when their job is done, they will in the shelters. Removing the netting survive in partial cuttings. Sheltering not simply disappear. They either will is important as the terminal leader natural seedlings eliminates the cost remain, sometimes damaging the tree, emerges to prevent it from getting of planting and protects the seedling or they will fall to the ground. They snagged and deforming the stem. from white-tailed deer. Shelter often break into pieces and, after a few seedlings in natural regeneration after years, can cause quite a litter problem. removing the overstory and prior to The type of shelter used affects ease of spring bud break. removal and cleanup.

3 The diameter of the shelter does not Color Things to Consider When have a large impact on survival. Large Color is discussed often but is not a Purchasing Tree Shelters diameters are more expensive to big concern, especially on sites that construct with no additional growth receive at least 6 hours of sunlight Tree shelters come in many shapes, benefit. In fact, the shelter effect is said a day. Try to plant seedlings in full sizes, and colors. The following dis- to decline as the diameter exceeds 4 sunlight to maximize the greenhouse cusses the range and types of shelters inches. However, reports indicate that effect in the shelters. The thinking to help determine which ones serve shelters less than 3.5 inches in diameter behind colored shelters is to mimic the best purposes. Traditional shelters cause the leaves to bunch up approx- nature, which implies a color between are made of translucent, twin-walled imately one-half to two-thirds of the clear and dark. In shaded areas such polyethylene. Most shelters are ap- way up the tree. As the tree produces as shelterwood harvests, it has been proximately 4 inches in diameter and more leaves, the shelter becomes more shown that seedlings in shelters grow up to 6 feet tall. Some newer shelters crowded, which may lead to mold at lower rates than in open areas, have special colors to reflect or absorb problems. Eventually the tree may stop no matter what the color. However, light, some are made of PVC pipe, producing leaves, affecting growth studies show that sheltered oak growth and some have holes or are made of and stem formation. However, little is best when chlorophyll absorption mesh or wire to provide ventilation. research supports long-term damage to is greatest, implying that nongreen Shelters are generally held in place by the trees. Some shelter producers allow wavelengths are best. Most modern plastic or wire ties fastened to wooden the diameter to expand by attaching shelters are light-brownish pink to stakes. Probably the least-costly ap- a second or third protector using lock provide this effect. White or clear proach in terms of materials is to use ties. One manufacturer produces a con- shelters allow the most light and are construction-grade plastic sheeting ical shelter, which goes from 8 inches at shown in some studies to produce with stakes and staples. the bottom to 4 inches at the top. the greatest height growth. Brown shelters, in the same study, were Shape Strength and Durability shown to reduce photosynthesis and The shape of the shelter whether Climatic conditions and growth. round, square, triangular, or hexagonal environmental factors affect a does not appear to have any significant shelter’s longevity. The ideal shelter Cost effect on seedling growth. The only provides microenvironmental Due to the relatively high cost of problem with nonround, folded needs and support and finally shelters, the first rule is to use only shelters is that they may split. Also, the disintegrates without cost for removal. the minimum number needed. tops of some shelters are modified— Polyethylene, the most common Depending on the management bent outward (flared) at the top—to material used, is strong and not toxic objective, this can range from fewer help reduce stem abrasion. when it decomposes. Ultraviolet than 50 to up to 400 shelters per light inhibitors are added to delay acre. If the site is a mixed planting, photodegradation of polyethylene for Size use shelters on the high-value species, approximately 5 to 8 years. Another There is a tradeoff between tree shelter those that are difficult to establish, material used is solid PVC pipe, height, cost, and release time. If deer or those that are highly preferred by which does not degrade quickly. browse is extensive, the shelter will deer. Often the landowner may plan need to be taller to afford the tree Some shelters have dual walls and are to plant more trees per acre but only more protection for a longer period of corrugated to add strength and rigidi- shelter half of them as insurance. time, thus resulting in a higher cost. ty. The more rigid, however, the better The second rule is that the higher the To determine the optimal height, the chance for stem abrasion, which deer impact, the fewer the plants per consider potential browse impact and may result in stem deformations. The acre and the more those plants need costs. Although 4 feet is the most durability and sturdiness of stakes sheltered protection. common size, shorter shelters are are also important. Iron, fiberglass, effective enough to provide growth plastic, or treated wood stakes are the enhancement, if deer are not a sturdiest. Make sure the stakes are well problem. More research is needed in secured to tree shelters—about 1 foot this area. deep in the ground and extend at least two-thirds of the shelter’s height. 4 costs associated with using shelters Table 1. Tree shelter prices. include material and labor. Labor is a 50 tree 100 tree 200 tree 400 trees variable cost dependent on whether shelters/acre shelters/acre shelters/acre shelters/acre you use a contractor or do the work Acres planted yourself. In addition, seedling, site 1 $150 $300 $540 $1,020 preparation, and planting costs are 5 $750 $1,500 $2,700 $5,100 obviously important to consider, 10 $1,500 $3,000 $5,400 $10,200 although not discussed in this pub- lication. Prices of shelters vary by manufacturer and quantity purchased. You also need to consider installation For example, compounding the pres- the costs of shelters from three ven- and maintenance costs. Labor costs ent value of the tree shelters at a 4 dors in 2004 for 4- and 5-foot-high include time to install the tree shelters percent interest rate shows that in 80 shelters ranged from $1.20 to $3.75 and place them over the seedlings. years the return on using 100 shelters each when a minimum of 50 shelters Some shelters come ready to use, oth- per acre ($300) needs to bring about were purchased. Prices decrease as the ers need to be assembled. Generally, $7,000 per acre in revenue at harvest. quantity increases. Stakes generally shelters are shipped flat to save on Many mature forests in Pennsylvania cost about $1.00 each. Table 1 shows mailing costs. Pre-assembled shelters currently do not provide that amount the cost differentials by quantity used require little on-site assembly and of revenue per acre from a timber har- and acres planted. In the example, the speed up installation. Be sure to read vest, but future stumpage prices are cost per shelter including the stake and follow manufacturers’ recommen- not predictable. is $3.00. Buying shelters in quantity, dations. however, reduces prices. In this ex- Selecting valuable species can make ample, prices are reduced 10 percent Once the shelters are in place, main- the investment more effective. ($2.70) for purchasing 200 or more tenance costs include weeding around Interplanting crops, herbs, fruits, and 15 percent ($2.55) for more than the shelters, straightening leaning shel- nuts, or other products can provide 400. Pooling resources and purchasing ters, and checking for insects, diseases, income while the trees are growing. shelters in bulk can be cost effective dieback, and animal damage. When Some government programs provide for landowners. maintaining, look inside shelters, financial assistance for tree plant- check for shelters and stakes that need ing. For example, up to $10,000 When does it pay to use fencing in- replacing, and remove netting when per year of reforestation costs can be stead of shelters if deer are the primary seedlings reach the tops of the shelters. deducted from federal income tax. concern? You can estimate that deer Reusing tree shelters and stakes can re- Some federal cost-share programs fencing in Pennsylvania—albeit the duce the cost. Nondegradable shelters such as the Conservation Reserve price decreases as acreage increases—is and durable stakes can be reused. Enhancement Program (CREP) and about $300 to $400 per acre, inclusive the Environmental Quality Incentive of installation costs (see Forest Finance The cost of tree shelters can be viewed Program (EQIP) provide cost-share 2). Note that the table of tree shelter as an opportunity cost of not having funding for shelters that provide en- prices does not include installation the seedling survive. Without the shel- vironmental services such as riparian costs. Both fencing and shelters re- ter, you may need to replace and re- buffers. quire periodic maintenance. The table plant new seedlings. Repeated failure shows that sheltering more than 100 and replanting can often exceed the seedlings per acre generally makes cost of the tree shelters. The financial fencing more economical, but fencing benefit of tree shelters is the opportu- generally does not become economi- nity cost of not using the protection. cal until many acres are involved. For In addition to replanting costs, this smaller acreages or if the plantings are benefit includes the value of knowing not adjacent to each other, trees shel- a future forest is regenerating or that ters may be more cost effective than water quality and riparian habitat are fencing. Along riparian areas or where protected. Looking strictly at financial narrow strips are planted, fencing is rates of return, you can argue that tree less cost effective. shelters are not a great investment.

5 Protex Pro/Gro Tube Tree Pro Tree Protector Sources of Tree Shelters Protex tree protectors consist of flat, Tree Pro tree protectors are flat, plastic sheets. The sheets are rolled polyethylene sheets that are formed A variety of shelters are on the market. into a cylinder to create a tube. into tubes using lock ties when placed Only a few manufacturers, however, around the trees. make them in lengths over 4 feet. As Terra Tech, LLC mentioned, most cost effective—but PO Box 2128 Miracle Tube Tree Shelter also most labor intensive—is using Eugene, OR 97405 Miracle Tube tree shelters are poly- plastic construction sheets. This mar- Phone: 800-321-1037 ethylene tubes. Miracle Tube can be ket is ever changing with new suppli- Fax: 800-933-4569 supplied in either vented or unvented ers coming in and old ones leaving. Email: [email protected] styles. New innovations and shelter designs Website: www.terratech.net are continually introduced. The fol- Tree Pro lowing suppliers are currently found Tree Sentry 3180 West 250 North on the Internet and are available for Tree Sentry tree shelters are 18 inches West Lafayette, IN 47906 use in Pennsylvania. You should exam- high and made of a photodegradable Phone: 800-875-8071 ine the different type of shelters each polymer. They have a unique, tapered, Fax: 765-463-3157 vendor provides and discuss situations conical shape and come completely Email: [email protected] with other landowners and natural assembled including integral stakes. Website: www.treepro.com resource professionals before deciding. Optional mesh tube extends browse Tubex Tree shelter protection to 4 feet. Blue-X Tree Shelter The Tubex trees shelter is made The Blue-X shelters are made of Summit Environmental Group, LLC from a chemically nonreactive and rolled, recycled X-ray film inserted PO Box 12267 biologically inert polypropylene. It in a poly sleeve. The inner, blue, 4500 N. Detroit Ave. consists of a seamless, twin-walled, plastic film can be stored for reuse. A Toledo, OH 43612 solid, translucent tube. The top rim replacement sleeve can be purchased 419-720-0185 of the tube is flared to protect the separately in order to reuse the plastic Fax: 419-720-0187 seedling. film. Email: sales@summitenvironmental .net Treessentials Company McKnew Enterprises Website: www.summitenvironmental 60 E Plato Boulevard PO Box 2128 .net Suite 130 Elk Grove, CA 95759 Saint Paul, MN 55107-1827 Phone: 888-472-5839 Phone: 800-248-8239 Fax: 916-683-4780 Fax: 651-681-1951 Email: [email protected] Email: [email protected] Website: www.growtube.com/shelters Website: www.treessentials.com .html

6 Shelters are expensive and their use Conclusion must correspond to management ob- jectives. Other options such as fencing Throughout their brief history, tree are available to control deer damage. shelters have proven to significantly Shelters can be economical, depending increase seedling survival rates. The on acres planted and number of shel- growth-enhancement benefits provided ters used per acre. The benefits of tree by the mini-greenhouse environment shelters help ensure that regeneration was the initial selling point of shelters. objectives are achieved. Through the A number of concerns emerged to use of tree shelters, species diversity highlight caution of wholesale shelter can be broadened, wood products can use. Concerns include shelter stability be grown, and a future food supply and durability, seedling stability after for wildlife, such as acorns for deer emerging from the shelter, and pro- and turkey, can be assured. Protecting tection from insects, diseases, birds, valuable species is important and, if and rodents that may damage or kill conditions warrant, trees shelters play the sheltered seedling. Today, however, an important role in assisting foresters shelters are used more for protection and landowners to achieve their land from deer browse and other nuisance management objectives. wildlife. Enhanced growth and survival have become secondary benefits.

Not enough research has been con- ducted about the impacts of shelters on long-term growth, but they clearly play a role in preventing browse dam- age. Research also continues on the in- teractions and effects of shelters with other established silvicultural practices such as competing vegetation control and fertilization.

Many different shelters are available on the market. Vendors tout different ben- efits in terms of color, durability, shape, and ventilation. No clear consensus as to the preferred type of shelter is avail- able. However, since the early days of shelters when most were dark, brown, and unvented, a shift toward a new generation of lighter-colored and vent- ed shelters has occurred, in part due to the combined effect on rodent damage, dieback, heat stress, and growth. In many cases, site-specific conditions and expected benefits from a shelter affect the choice of shelter. Whichever type of shelter used, it must be monitored and maintained. Without adequate mainte- nance, you can expect a relatively high failure rate.

7 Prepared by Mike Jacobson, assistant professor of forest resources, and Dave Jackson, forest resources extension edu- cator.

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