![\"Contrary](\"http:\/\/blogs.northcountrypublicradio.org\/allin\/files\/2015\/05\/rootsystem.jpg\")
<\/a>Contrary to popular belief, 98% of a tree’s root system is in the top 18 inches of soil, and extends out well beyond the canopy in a “root plate”. Image: UCDavis<\/p><\/div>\n
Part of the issue stems from a flawed understanding of tree biology. There is a lot of tree-root apocrypha floating around the public consciousness. One myth \u2014 let\u2019s call it the Legend of the Big Taproot\u2014 maintains that trees make enormous deep taproots. While the legend allows that a few side roots may branch off, the key element is the Big Taproot.<\/p>\n
It\u2019s true that trees such as oaks and walnuts have a significant taproot when they\u2019re young, but in maturity their root systems look like a pancake, not a carrot, the same as other tree species. Most of us have seen trees that have blown down, but that monster taproot has yet to be spotted. It\u2019s no coincidence that the flat root system one sees on a windthrown tree is referred to as a root plate<\/em>.<\/p>\n About 90% of tree roots are in the top ten inches of soil, and 98% are in the top eighteen inches. A tree\u2019s roots extend, unless there\u2019s an obstacle like a road or building, at least twice the length of its branches. This is a tree\u2019s root zone, a broad, shallow, vulnerable mass of roots.<\/p>\n Sadly, the Big Taproot Legend has dreadful health implications. For trees, at least \u2014 who knows what it portends for our well-being. If we believe tree roots like it deep, we won\u2019t think twice about adding soil or fill, or even paving some of the root zone.<\/p>\n What\u2019s wrong with that? To survive, roots need oxygen, which they get directly from soil pores. Even though they make oxygen when they photosynthesize, trees can\u2019t transport it through their vascular tissues that work so nicely for carrying water, sugars, and nutrients.<\/p>\n Soil compaction from operating vehicles or equipment within the root zone causes the same problems. In wet soil conditions, even excessive foot traffic can cause enough compaction to mash soil pores shut and exclude oxygen. In these cases, roots slowly suffocate, and the tree will eventually show symptoms of decline.<\/p>\n Excavating or trenching within a root zone severs some tree roots and usually compacts the rest. Sometimes root damage will kill a tree outright within a few years, but more commonly there will be a prolonged decline over five to ten years or more. Because of the time lag, secondary, opportunistic agents often get the blame.<\/p>\n As with relationships, where trees are concerned the problem at hand is often not the real issue. Imagine glancing out the window one day to see wood chips the size of baseballs raining 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, power-sawing their way down the trunk. As they smirk at you atop the mound of pine chips, you search the Internet for an exterminator, knowing you\u2019ll miss sitting under the pine\u2019s yellow foliage.<\/p>\n Wait a minute! Yellow foliage? How long was it like that? Maybe there\u2019s 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 (bugs, not scientists). It will endure some loss due to insect feeding, but it will be able to keep the balance in its favor.<\/p>\n Let\u2019s think back on your white pine. Wasn’t that the one that you worked so hard not to hit with the backhoe when the septic went in six years ago? Or was that the one the gas company trenched near ten years ago? It doesn’t matter. Human activity compromised the root system and resulted in the demise of the tree years later. Sawflies or no, that pine was doomed.<\/p>\n By now you may be thinking, I could sure use another coffee, or, how do trees in those little concrete squares (tree pits) in the sidewalk survive? The difference is that they are put there as little tykes and never come to depend on a normal root system. They’ve adapted to available root space and are considered \u201cunhappy.\u201d Mature trees that have a large root system suddenly cut or damaged to the size of tree pits are considered \u201cdead.\u201d<\/p>\n You can preserve trees in a construction site by cordoning off the root zone at least to the tree’s drip line (branch length) with snow fence before the project begins. Keep in mind that even stockpiling material under trees causes root damage. If driving near trees is unavoidable, adding four to six inches of wood chips or gravel (two-inch or larger) to the traffic pathway will help.<\/p>\n