A tree's root system, vital to its health and survival, serves several purposes. Roots collect moisture and nutrients from the soil and transfer them to other parts of the tree. During a tree's dormancy period, the root system serves as a storage area for food the tree will need when it resumes growth.
Woody or Large
Woody roots, also called large roots, typically grow in the top 6 to 24 inches below the surface, although they can extend 3 to 7 feet deep in some cases. Woody roots grow laterally and anchor the tree in the soil. These roots provide the basic framework for a tree's entire root system, according to the University of Iowa Extension. They might extend as far as four to seven times a tree's drip line. Woody roots also create annual growth rings.
The feeder root system grow of out the woody root framework. Feeder roots, much smaller than woody roots, have a diameter of about 1/16 inch and make up the majority of a tree's roots. Feeder roots usually grow close to the surface, since their primary function is to absorb nutrients from the soil and these typically accumulate at a shallow depth.
Taproots, large central roots that grow deep into the soil, might or might not develop as part of a tree's root system. Whether a taproot becomes established depends on the tree's species and the conditions in which it grows. When a tree grows in compacted soil or can obtain sufficient moisture near the surface, it usually does not develop a taproot, reports the University of Florida. Taproots might also diminish as the woody root system becomes more extensive. Taproots rarely appear in trees planted in urban landscape, as the compacted soil of these areas inhibits their development.
Striker roots, roots that grow downward from the main root structure, sometimes occur in certain species growing in dry soils. They continue downward until they hit an obstruction or encounter soil with insufficient oxygen. At this point they might create a second layer of horizontal roots.