Northern Woodlands

The Root of the Problem

June 01, 2008

by Paul Hetzler

As far as trees are concerned, root damage is the root of all evil. Well, most of it, anyway. No matter what symptoms are visible – early fall color (a sign of stress), sudden death of branches, twig dieback, pale or unusual leaf color, slow growth, even some diseases and insect infestations – the problem is likely belowground.

There’s a lot of tree root apocrypha out there. One myth – call it the Legend of the Big Taproot – maintains that trees grow huge, deep taproots. Oh, there may be a few side roots branching off, but the important part is the Big Taproot. Actually, while some tree species have a taproot when young (such as oaks and walnuts), most mature root systems look more like a pancake than a carrot. About 90 percent of tree roots are in the top 10 inches of soil and they extend, or try to extend, two to three times the branch length. Most of us have seen trees that have blown down, but that monster taproot has yet to be spotted. It’s no coincidence that the flat root system one sees on a windthrown tree is referred to as a root plate.

It’s not just that I like to be right; the Big Taproot Legend has terrible implications for tree health. If we think tree roots are deep and that they like it that way, we won’t hesitate to create nuisances within a tree’s root zone such as trenching, excavating, paving, adding fill, building, driving, parking, or line dancing. Digging-type activities sever tree roots and usually provide a side order of compaction as well. Most other activities mentioned cause compaction and subsequent root death.

What’s wrong with compaction? For roots to survive, they need oxygen, which they get directly from pores in the soil. They don’t get it from those handy vessels in the tree’s bole that carry water, sugars, and nutrients, but can’t transport oxygen. When a tree’s root zone becomes like cement (or becomes cement, as the case may be), pore spaces are mashed shut and roots suffocate. Adding fill has the same effect as compaction: it excludes oxygen. Sometimes this kind of damage will kill a tree outright within a few years, but more commonly, there will be a prolonged decline, with secondary, opportunistic agents often getting the blame.

What happens when only part of a tree’s root system is compromised? Well, you get a stressed-out, cranky tree (not to be confused with a crabby apple), which will be vulnerable to opportunistic Bad Things later on. Trees have complex defense systems, but in order for them to work properly, a tree needs to be happy, with all parts in good working order. A cranky tree with damaged roots won’t be able to manufacture and transport sufficient fungi-resisting chemicals to a wound site, for example, and will be subject to more extensive decay than a happy tree. This also relates to insects.

The problem is often not the problem, if you know what I mean. Let’s say you’re relaxing in the La-Z-Boy looking out the window, when to your shock and dismay, wood chips the size of baseballs rain down from your favorite white pine. You rush outside (with your Kevlar umbrella) and discover an army of Jig Sawflies, their carbide blades freshly sharpened, finishing off the stump at ground level. You rifle through the phone book for an exterminator, knowing how you’ll miss sitting in the pine’s shade, enjoying its yellow foliage. Wait a minute! Yellow foliage? How long was it like that? Maybe there’s something else going on here.

A strong, happy tree will be able to respond to insect feeding by manufacturing chemicals known to scientists as Bad-Tasting Stuff to repel them (the bugs, not the scientists). It will endure some loss due to insect feeding, but it will be able to keep the balance in its favor. Let’s think back on that white 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? Or was that the one the gas company trenched next to seven years ago? The same one the painter kept dumping solvents by? It doesn’t matter. The point is that human activity compromised the root system, resulting in the demise of the tree years later. Sawflies or no, that pine was doomed.

What about those trees in little concrete squares (tree pits) in the sidewalk – how do they survive? The important difference is that those trees were put there as little tykes and haven’t come to depend on a normal root system. Trees grown in tree pits have adapted to available root space and are considered “unhappy.” Trees grown in larger areas that have their roots cut or damaged to the size of tree pits are considered “dead.”

Trees have environmental benefits; that’s no surprise, but there are social and economic benefits as well, particularly trees near our homes and in our communities. In fact, there’s a positive correlation between the presence of trees in one’s life and a reduction in stress symptoms. So let’s keep those trees thriving. Do mulch the root zone – the whole thing if you can. Don’t drive or park within the root zone; don’t add soil to the root zone or create raised bed gardens around trees, and do try to keep line dancing to a minimum. And look down, not up, to find what’s bugging your trees. An event that damages roots may take years to show symptoms – 5 to 10 years is not uncommon. Your job is to keep those trees happy.

Paul Hetzler, a graduate of Paul Smith’s College, has been a practicing arborist since 1992. He lives in Canton, New York.

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© 2008 by the author; this article may not be copied or reproduced without the author's consent.

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