Oak tree's roots illustrate finely tuned growth system

Oak tree's roots illustrate finely tuned growth system
Date Published: January 20, 2006

Oaks make lots and lots of roots. No matter what, they stand a chance of survival. Within the first year, the taproot of an oak can reach more than a foot in depth. Though the taproot later declines in importance, it spends the first few years thickening and storing as much food as it can.
The root is like an auger, opening the way in the soil. Roots can travel pretty fast, up to 25 millimeters in a day. If you were patient (and able to see through soil) you could watch them grow. Half the total food that the tree makes each year goes to grow new roots.
Roots may circle from necessity, but they try to grow outward in straight lines. The lateral roots of a large, open-grown oak stretch hundreds of yards from their origin. They sense and respond to irritants - rocks, water-saturated zones, poisons - as finely as the human tongue, and they are stronger and more intelligent than a human finger or arm.
If a growing root encounters a stone, it may compress slightly, deflect to one side and return to its straight line once the obstacle has been passed. Or, if it senses the slenderest crack in the rock, it may splay out thin and grow right through the fissure to the other side.
They know where they are. They know how deep they are in the soil, because they test the amount of oxygen and water around them. Where there is more oxygen and sufficient water, there is more growth. Yes, you could describe this as intelligence.
It was once thought that the tree's branches and its roots were mirrors of each other. But this is not so. Botanists found this out when some extremely patient Scandinavians painstakingly scraped away the soil from the root systems of several mature trees.
They had thought they would run out of roots at about the same distance as the dripline. No, the roots kept going - many feet. The roots got smaller and more numerous toward the tip. They gave up when the distance of the root mass from the trunk was nearly three times as wide as the maximum spread of the tree's canopy. And there were still more roots beyond.
Most smaller roots live four years or less, some for as little as a season or even a week. Many of the pencil-lead and thinner roots die and are replaced several times in one year.
Root hairs - the almost microscopic hairs that work with beneficial fungi bringing nutrients and water into the tree - may be replaced every few hours. Yet the average mature red oak has better than 500 million living root tips.
Root growth in oaks is doubly persistent. While the leaves sprout three or four times each year, the roots grow continuously from March to October, and in some climates into November.
The biggest spike of growth occurs between May and late June in the temperate northern hemisphere, with a small spike between late August and early October. In our Mediterranean climate, all tree roots on our property must be deep watered each summer two to three times per month to 12 inches. They do not function in dry soil.
It is not a good thing to risk damaging the roots, for it is these upon which the oak's life depends.
Jean Pliska is a certified arborist.