Talking trees have been a fixture in folklore and fiction. If you’ve ever watched The Two Towers, the second movie in the Lord of the Rings trilogy, you would have seen the giant tree-like creatures called “Ents.” Talk? The Ents practically wouldn’t shut up.
If trees could really talk to us, it might be a simpler matter to keep them safe and healthy. But they can’t, so, just as with our pets and other animals and plants we tend, it’s up to us to monitor them for signs of ill health.
Most landscape and irrigation contractors are not arborists, nor do they need to be. However, trees are part of the landscapes that they’re being paid to care for, so a little more knowledge about them is certainly in order.
Signs of stress
When you were little and caught a cold, your grandma might have told you that you looked “pekid.” It’s the same with trees. When they feel poorly, they look it.
Deciduous trees signal sickness by leaves that turn “chlorotic”—yellow, at a time of year when they should be green. Or leaves may hang down abnormally, a condition called “leaf wilt.”
Next comes out-of-season leaf drop. “Trees will drop leaves as a means of protecting themselves, to reduce water loss and stress,” said Rob Gorden, director of urban forestry at Arborjet, Woburn, Massachusetts.
Stressed trees may also produce an excessive number of seeds. “It’s like they’re saying, ‘I may be dying, so I’m going to produce a lot of seeds to continue my species.’” Beyond that, as decline progresses, you’ll see dieback of small limbs and then, even smaller limbs. The trees are doing the same thing we humans do when we suffer frostbite. Our bodies shut down the blood flow to our extremities in order to preserve our vital organs. If you wait until you see this woody-tissue dieback, you’ve already gone pretty far down the stress road.
What causes trees to become stressed? Mainly drought, insect infestation, disease, injury and weather.
The Northeast and Midwest just came through one of the worst winters in recent memory. Some trees may not have survived it, unless someone know enough to protect them the previous fall.
Sun scald sounds like something that happens when it's hot. It is, but it can also hurt trees during the winter. It happens when bark heats up on cold winter days, then chills down rapidly when the sun sets or ducks behind a cloud.
Here's how it works. Warmth causes growing tissues near the surface of a tree to 'wake up,' or became active; then, a sudden temperature drop kills them. Sun scald shows up as a sunken, darkened area of bark, usually on a tree's south side. Thin-barked trees are more prone to suffer from this.
Wrapping the bark of susceptible trees during the late fall with treewrap tape, plastic tree guards, or a similar light-colored material can protect against sun scald. Take these coverings off in the spring, after the last frost, or it’ll become a shield for summer insects. New or young trees should be wrapped for at least two winters; thin-barked species for five.
Evergreens can also suffer from cold. The evidence of this is browned leaf tips or needles from loss of moisture by wind or sun. That’s why you should water evergreens well before winter starts, because they can’t draw it up once the ground is frozen.
Expansion and contraction of soil from repeated freeze-and-thaw cycles is called ‘frost heave.’ This can damage roots and even chuck new plantings right out of the ground. Plan your plantings so that new trees will be well-rooted by fall.
“There’s only so much you can do with the part of the tree that’s above ground, to protect it,” said Tim Wright, CEO and co-owner of Carrboro, North Carolina-based Wright Brothers’ Landscaping and Tree Service. “During the winter, most trees are dormant or semi-dormant. What really needs protection are the root zones.”
Those roots need a cozy blanket, whether that’s leaf or wood mulch. Wright says this layering makes a big difference in the soil temperature below. Snow is a good insulator, too. “If it’s ten degrees below zero, the soil temperature will be very different under two feet of snow than in places where someone has plowed all the snow off.”
Native trees that have evolved in cold climates are going to do better, of course. But as we all know, plenty of non-native trees have been planted where Nature never intended. They’ll need extra help.