Home Is Where Your Trees Are

Tree Structure. Roots. Part 1

The upper parts of a tree inevitably monopolize our attention. The trunk and crown, the leaves, flowers and fruit, are what we can see and enjoy. When they think about their trees' care, owners are prone to ignore the root systems - out of sight, out of mind. And this imbalance of emphasis is not confined to laymen. The scientific study of roots has lagged far behind other branches of dendrology. A few years ago an important but not widely publicized contribution on root systems was made by Benjamin B. Stout, now on the Rutgers forestry faculty. He and two assistants spent the summers of 1951-52 in Harvard's Black Rock Forest near Cornwall-on-Hudson, N.Y., laboriously exploring trees down under. Mr. Stout selected twenty-five typical specimens representing nine deciduous species, all growing in light, comparatively shallow highland soils, and ranging in age from 17 to 104 years, in height from 21 to 67 feet.

The digging was to be done hydraulically, with strong jets of water to unearth and gentler streams to wash clean every part from deep taproots to the hairy tips of long laterals. So trees on sloping sites were chosen, to let the hose-water and soil drain away. This also made it easier to photograph the naked root systems in profile. (See Photo. 2.) Before its roots were laid bare, each tree was felled and its upper parts laid by for correlative study.

Exposing Root
Exposing Root Systems

Mr. Stout's measurements, ring counts, and other data were illuminating not only to dendrologists. They also contained broad hints for home owners. Most importantly they revealed that the average tree's root-spread is far wider than had been supposed. Instead of approximating their crowns' spread, the roots of Mr. Stout's trees reached out into areas 3.4 to 40.7 times as great as the ground-space under the crowns. (See Photo. 2 and diagrams. Dotted lines show crown areas, as contrasted with root reaches in solid line. Graphs give stem ( - 0 - ) and root ( - x - ) growth data in feet and years. Circles initialed CO, WO, RM, etc., denote neighboring chestnut oak, white oak, red maple, etc.) Eighteen of the trees appeared to have normal root systems; for these, the root-crown ratio averaged 4.5 to 1. Since the Black Rock trees had grown under forest conditions, with their crowns touching, this meant that each tree was competing for sustenance with at least three of its neighbors.

White oak root
White oak root systems
Chestnut oak, red maple root systems
Chestnut oak, red maple, sugar maple root systems