By PAUL HETZLER
They might all be right: for Hindus and Buddhists, the cause of suffering is desire, while Christians believe the origin of all evil is the love of money. And as far as trees are concerned, root damage is the root of all problems. Well, most of them, anyway.
Whether it’s early fall color (a sign of stress), twig and branch dieback, pale foliage, slow growth, or even some diseases and insect infestations, the problem is usually below ground.
If the next Google Glass offers ground-penetrating radar, it’ll be a lot easier to find buried treasure. And we’d be able see that about 90 percent of tree roots reside in the top ten inches of soil, and that they extend (unless there’s a barrier) two to three times the branch length. In profile, the root system of any tree—even “deep-rooted” ones like oaks—is pretty flat. It’s no coincidence that arborists refer to root systems as root plates.
Because we can’t see into the ground, treasure-hunting is out and we have to keep our day jobs. And also, we’re likely to assume that tree roots are generally deep and that they like it that way. So it’s not surprising we don’t think twice when it’s time for trenching, excavating, adding fill, building, or even driving within a tree’s root zone.
Damage is obvious when an excavator cuts tree roots, but many other events cause compaction, a less visible problem. For roots to survive they need oxygen, which they get from soil pores. (Vessels in wood that transport water, sugars, and nutrients don’t carry oxygen.) When soil gets compacted, pores disappear and roots suffocate. Adding fill has the same effect; it excludes air. Such damage may kill a tree within a few years, but more often there will be a prolonged decline. In these cases, opportunistic diseases and insects may be the proverbial last straw.
Trees have complex and effective defenses, but for them to work well, trees need to be happy, with all systems in good working order. A strong tree can respond to insect feeding by making chemicals known to scientists as “bad-tasting stuff” to repel them (insects, that is, not scientists). It will endure some loss from insects, but will keep the balance in its favor. A crabby tree with damaged roots, though, won’t be able to make sufficient antifungal chemicals at a wound site, or create enough insect-repelling compounds the way a healthy one can.
So the problem you see may not be the real problem. Let’s say you look out the window one day and to your horror, notice a torrent of sawdust raining down from your favorite white pine. Umbrella in hand, you rush outside and find a swarm of Jig Sawflies (cordless, naturally), their carbide blades freshly sharpened, chewing your pine to bits.
As you rifle the phone book for an exterminator, you think how you’ll miss sitting in the tree’s shade, enjoying its yellow foliage. Wait—yellow foliage? How long had it been like that?
Let’s think back on that pine. Wasn’t that the one that you worked so hard not to hit with the backhoe when the septic went in five years ago? The one the gas company trenched near ten years ago? Human activity can compromise a tree’s root system, resulting in its demise much later. An event that damages roots may take 5 to 10 years to show symptoms. Because insects are attracted to a declining or dying tree, they’re often assumed to be the culprits.
Right now you may be wondering, “What’s on TV?” or, “Will this guy get to the point?” or maybe, “How do trees in little concrete tree pits in the sidewalk survive, then?” Those trees were put there when young and have adapted to available root space. In technical parlance, they’re “unhappy.” Trees grown in the open that suddenly have their roots cut or damaged to the size of tree pits are considered “dead.”
We all know trees have environmental benefits, but they have social and economic value as well. There’s a positive correlation between access to trees in one’s life and a reduction in stress symptoms. Planting trees in a neighborhood leads to a reduction in crime. Trees add substantially to property values. So let’s help them thrive. Don’t drive, park, or add soil within the root zone. Mulch the area about four inches deep, and water during dry spells.
Keep those trees happy, and they’ll keep you healthy.
Paul Hetzler is a forester and Cornell Cooperative Extension of St. Lawrence County horticulture and natural resources educator.