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Root systems can reveal underground secrets

  • Roots poke out above the ground in a forest. pixabay.com


Saturday, November 05, 2016

The brilliant autumn leaves of October have faded and are being ripped from their branches by November winds, so this is a perfect time to think about other parts of trees, namely the roots.

Tree roots have several functions. They absorb water and minerals from the soil, essential for tree growth. Some roots provide stability, holding trees in the ground. Roots also provide a place for food storage.

Food storage is important, particularly in our climate. When nutrient-producing leaves die and are shed in the fall, the tree must have a way to jump start growth after winter dormancy. Sugars created in the summer leaves are converted to starch, stored in the roots during winter, then turned back to sugars and sent up to the branches to nourish the buds as they emerge in spring.

The varying roles of roots require different root types. When a seedling begins to grow it produces a tap root that reaches straight down into the soil to anchor the new plant in the ground. As the stem and leaves grow on the surface, additional roots expand underground. Lateral roots branch off the tap root. These form close to the surface of the soil where most of the water and nutrients are found. Thus a wide matt of roots radiates out from the trunk, parallel with the soil, creating a “root plate”.

As the roots branch, they often intertwine and rub against each other. This may enable them to fuse together in a kind of natural graft. These added connections build strength in the root matt and facilitate flow of water and nutrients.

Different trees have various strategies for root growth and that is also influenced by the type of soil in which they grow. Spruce and fir trees which are found primarily in northern and mountainous regions where the soil is shallow, have more surface roots. By contrast, oaks, which grow in richer and deeper soils, have deeper roots.

In general though, the roots of most trees are thick and woody near the trunk and get gradually finer, tapering to string-like fibers as they fan out. As roots grow they follow cracks, worm tunnels, old root channels and the easiest path toward water. The finer roots and tiny root hairs that grow on their tips create innumerable contacts with the soil. Scientists estimate that a mature red oak might have up to 500 million live root tips. If the root tips encounter an obstacle as they are growing, they will fork and grow around it, often encompassing a rock in a tight grasp. This actually helps to anchor the tree into the soil.

The stabilizing role of roots is accomplished by both deep and shallow roots. The breadth of a root system typically exceeds the width of the tree canopy by two to three times. However, in extreme conditions even this massive anchoring system is not enough to hold the tree to the earth. Heavy winds and storms can cause blowdowns of living trees, often (but not always) leading to its death.

The remnants of blowdowns can give us a glimpse of the intricacy of roots and provide a clue to the meteorological history of the area. When a tree blows down, the finer roots will break and stay in the soil but the root plate will rip up from the earth bringing with it soil and rocks.  A large hole will be left in the ground. This is known as a pit.

Over decades the exposed roots will begin to decay, soil will drop from the clump and a mound of debris will form where the root matt was. Long after the downed tree has returned to the soil, this “pit and mound” formation will remain. If you stand on the mound and look over the pit you will be facing the direction from which the tree-toppling wind came.

This directional information can be seasonally diagnostic. Blowdowns from western winds generally occur during summer storms. Northwestern winds are more common with fall and winter storms. Southern and northeast winds are usually associated with fall hurricanes and winter nor’easters.

So the next time you are in the woods and find an uprooted tree, take a closer look to appreciate the configuration, function and history of this important but usually hidden structure.