It is well known that the boles and crowns of trees frequently attain massive proportions. The fact that the root system also attain great size, extending vertically into the soil and spreading out laterally, is less generally recognized. As a rule the lateral extention of a tree’s roots is greater than that of its crown. This places an ever increasing strain on the supporting roots since with increasing length of the bole, leverage becomes greater. Further, the higher a tree crown rises above the ground level, the greater are the wind velocities to which it is subjected.
Uprooting of trees by wind is universal in forest regions. Scattered individuals or groups of trees, and even entire stands, are destroyed when air movement becomes sufficiently violent. This fact is confirmed by common experience. In some cases the force exerted on a tree by wind results in breakage in the crown or bole; in other cases the tree Is uprooted. The latter is especially to be expected when the trees are tall and shallow rooted, and when growing in exposed topographic situations and on shallow or wet soils. Even deep rooted trees growing In well drained upland soils are uprooted by strong winds which follow periods of unusually heavy precipitation.
While investigating tree-root distribution in the Yale Demonstration and Research Forest near Keene, Hew Hampshire, the writer was impressed by the extent to which the soil body in certain areas had been disturbed by the uprooting of trees. During the next year the writer undertook an investigation of the morphological features of soil mounds and depressions resulting from windthrow.
As work on the morphology of soil mounds progressed it became evident that disturbance of the soil material had resulted in other equally striking changes. Consequently a number of physical and chemical properties were investigated. The objective was to determine the influence of soil disturbance, by the uprooting of trees, on various soil
properties believed to have ecological and pedological significance.
It has been shown that, as a result of disturbance, horisons may be very Irregular, occasionally with long tongues from the upper layers penetrating deeply into the layers below. Further, horizons may be discontinuous and masses of soil material may be translocated to positions above or below those normally occupied, frequently, material from upper and lower horisons is rather Intimately mixed. The vertical and horisontal movement of rocks two or more feet in diameter evidence of the tremendous forces involved. In short, disturbance of the upper three or four feet of the soil body by tree roots may be manifested in exceedingly diverse ways.
Soil disturbances by tree roots are regarded as important from several points of view. First, and most obvious, is the fact that a variety of microrelief features are created. This variety of micro-relief features should tend to favor variety In vegetation composition. Recent work has emphasized the ecological importance of micro-relief in the establishment and development of forest trees. Further, as a result of disturbance the soil body exhibits greater heterogeneity, both vertically and horizontally, difficulties of soil sampling are increased.
Undisturbed podzols frequently have a considerable accumulation of organic debris overlying the mineral solid. Disturbance of the soil by uprooted trees results in burial of this organic debris or mixture with mineral material.