Purdue News
Purdue News
"I suppose there are some people out there who don't like trees, but I haven't met them," said Rita McKenzie, an urban forestry specialist in the university's Department of Forestry and Natural Resources. "Most people are aware of the benefits of trees."
Still, she said she has seen numerous examples of tree abuse, where people through ignorance or negligence have inflicted grievous injuries on otherwise hardy hardwoods.
The most frequent culprit is a homeowner with a weed whacker who trims right up to, and all around, the base of the trunk. The bark is stripped, tearing off the tree's first line of defense against the vagaries of nature and often interfering with the tree's ability to feed itself.
"Right next to the bark is the phloem, a system of tiny tubes that transports sugar and other food from the leaves to the roots. Cut far enough in and you'll disrupt the xylem, the system that moves water and nutrients from the roots to the rest of the tree" she said.
Head-on collisions with lawn-mowers would accomplish the same thing, as the sharp edge of the mower's metal casing can gouge out significant chunks of bark, she said.
Indiscriminate pruning also can open a tree up to insects, disease and other insults. Cutting a branch flush with the trunk makes a larger wound that takes the tree longer to seal. A more prudent approach would be to make the cut just above the branch collar where branch meets trunk, she said. The branch collar contains chemicals that allow the tree to close off the wound and shut off easy access to invaders, she said. Getting carried away and cutting off more than 50 percent of the crown -- the leafy part of the tree -- can impair the tree's ability to photosynthesize sunlight into tree food.
Other above-ground activities that can harm a tree include allowing broad-leaf herbicides to drift into the leaves, letting salt accumulate from driveway de-icing, and putting mulch right up against the trunk. The mulch can hold water and rot the bark, and too much mulch may trick feeder roots into growing above the soil where they're more vulnerable.
Even if a tree avoids all these above-ground insults, it still can fall victim to abuse, said Paul Pecknold, a tree disease specialist in Purdue's Department of Botany and Plant Pathology. He said the root of most tree decline problems can be found largely in the roots. Tree decline is insidious -- trees gradually lose vigor over years and may show off-color leaves, leaf scorch, poor growth, early leaf drop and dieback of twigs and branches.
He lumped those problems into a category he called "people-pressure diseases," because they often result from human activities. "Tree problems are usually the result of ignorance, those harmful things people do to trees because they don't understand how trees function. The roots catch most of the abuse because anything you don't see, you don't think about," Pecknold said.
Any digging around a tree can have lasting negative effects, because it could interfere with the feeder roots that take up moisture and oxygen from the soil, he said. The feeder roots live in the top six inches of soil, concentrated under the edge of the canopy. "It can take 10, 20, 50 or 100 years for the feeder roots to get established at their optimum level, and 10 minutes with a trencher or a shovel can wipe them out," Pecknold said. He advised homeowners to think about what's under the ground so they might shift a planned sprinkler line or electrical wiring away from the tree.
Soil compaction around the tree is a common root problem, where foot traffic, a parked boat trailer or kids playing can tamp dirt down like concrete, blocking feeder root growth. Moist spring soils are especially vulnerable to compaction.
Adding soil around the tree also can have long-term ill effects, especially for certain species. "There's the old joke that just standing next to a beech tree and talking about adding soil will make it drop leaves," Pecknold said. Putting any amount of soil over the feeder roots would effectively suffocate the tree, cutting off air and water, he said.
The most significant symptom of root decline is die-back of the very top branches, where the weakened tree can't muster the muscle to move the water up to its highest parts.
Pecknold said tree decline is due to a combination of stress factors working together over several years. Damaged or weakened plants are more prone to drought stress, winter temperature extremes, insects and diseases. These secondary problems often can be the final blow that results in tree death: "When people get sick they're more susceptible to other illnesses. It's the same with trees."
Prevention is the best treatment, but for those who have second thoughts about letting the tree wither away, Pecknold said some trees can be rescued. Deep water the tree during extended dry periods, aerate compacted areas, treat major insect infestations, and trim away dead branches so they won't attract wood-boring insects, he advised. Heavy fertilizing would be a mistake, because it would spur the plant into growth it couldn't sustain, Pecknold said.
"Tender loving care will allow the tree to find its own balance," he said.
Sources: Rita McKenzie, (765) 494-3625; e-mail, Rita=McKenzie%GradStudents%fnr@forest1.fnr.purdue.edu
Paul Pecknold, (765) 494-4628; e-mail, pecknold@btny.purdue.edu
Writer: Chris Sigurdson, (765) 494-8415; e-mail, sig@ecn.purdue.edu
Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu
NOTE TO JOURNALISTS: National Arbor Day is April 25.
