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New Mexico State University

New Mexico State University

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Unwrap Trunks for Healthier Trees

LAS CRUCES -- Wrapping trees with protective trunk materials can cause more harm than good, said a New Mexico State University forest entomologist.

"Wrapping was thought to protect trees from temperature changes, drying out, and chewing critters, but new research suggests that wrapping trees with protective trunk materials can cause serious injury," said Bob Cain with NMSU's Cooperative Extension Service.

The most common protective material used in the United States is white paper wrap, according to the International Society of Arboriculture (ISA). The material is said to protect tree trunks from drastic changes in bark temperature, which can lead to sunscald and frost cracking. This is the same reason many fruit and nut tree trunks are painted with white latex paint.

"While white materials painted on tree trunks may cause cooler bark temperatures by reflecting heat, studies have shown severe temperature changes have occurred beneath tree wraps," Cain said.

Some people use the wrapping to protect trunks from drying winds. ISA reports that in some cases so much moisture has been held under the wraps that trees actually grew roots along their trunks.

Cain and Jim Freeman, urban forestry coordinator with the State Forestry Division, spent an afternoon in April unwrapping tree trunks covered by paper wrap. The trees had been planted 16 months earlier in Santa Fe.

Despite a very dry winter, the paper wrap retained moisture against the bark of the trees. Cain said freezing and thawing appeared to have caused some bark injury and may have allowed entrance of disease fungi.

Some trunks were infected with fungi commonly found on weakened trees, and the moist conditions provided habitat for many insects. Cain and Freeman also saw abnormally enlarged bark pores, which may serve as entry points for borers or fungi. The trees also were being girdled by the twine used to secure the wrap and by cord used to tie the trees to stakes.

Some trees such as cottonwoods, hybrid poplars and aspen have photosynthetic bark, which needs sunlight. On wrapped trees, the bark chlorophyll breaks down, leaving the trunk discolored, Cain explained.

"It is especially important that tree wraps be removed in early spring before trunks expand," Cain said. "This also is the time to evaluate and probably remove materials used to stake or stabilize trees when they were planted."

Only top-heavy trees transplanted from containers usually require staking, he added. Once the tree is firmly established, wires and similar materials used to tie trees to stakes must be removed. If tie material is not removed, trees may be girdled or constricted. Trees with constriction injuries often break in high winds.