Tree Roots

Trees can grow to a very large size both above and below the ground. The roots of a tree, though not visible, are vital to the functions of a tree. Tree roots have three important functions: they anchor and support the tree, store energy as starch during the winter, and absorb water and soil nutrients during the growing season. Some but not all trees have a tap root, which grows straight down for a number of feet and helps support the tree. Trees with well defined tap roots include hickories, walnut, and white oak. The woody buttress roots grow from the trunk of the tree down a few feet and these roots help support and anchor the tree to the ground. The feeder roots are woody but they have fiberous root hairs as well; and, they typically grow outward from the tree and are rarely deeper than a few inches to a foot below the surface. These feeder roots are involved with the uptake of water and nutrients. Feeder roots are always actively growing unless the soil is frozen during winter; their function is to support the above-ground portion of the tree. Sometimes feeder roots grow well beyond the extent of the crown “drip line” of a tree in search of adequate nourishment. Often times fungi called mycorrhizae will attach to a feeder root, forming a mutually beneficial “symbiotic” relationship whereby the fungi enable the tree to obtain needed nitrogen from the soil and the mycorrhizae live off some of the trees energy reserves in return. In the fall a tree will begin storing excess energy reserves in the form of starch in the buttress roots. This starch will provide the initial flush of energy necessary to allow for bud break and leaf expansion in the spring.

A healthy tree has an innate balance between its roots, trunk, and crown. Damaging roots can make the tree unstable so it can topple over or limit the tree’s ability to obtain needed water or nutrients. Damaging the buttress roots can result in loss of tree stability, or it can permit decay, allowing fungi into the base of the tree which will slowly erode away the main support roots. The feeder roots can be easily damaged since they are smaller and lie in close proximity to the surface. These feeder roots can be damaged by digging, piling additional soil or removing existing soil around the tree, applying herbicides, crushing the roots by moving heavy machinery around the tree or compacting the soil around the tree by regular foot traffic. Damage to significant feeder roots can disrupt the balance between the roots and crown and result in dieback in the canopy. Certain allopathic plants can also harm a tree, usually by producing natural herbicides that could kill feeder roots or harm the symbiotic mycorrhizae that are important for nitrogen uptake in trees. Many of our exotic invasive species out-compete native plants by disrupting the symbiotic mycorrhizae of the native species. When newly transplanted trees receive abundant water, their roots do not have to develop as much to meet their requirements.

If that water source is removed abruptly, the tree may not have adequate feeder roots to support it during severe drought. Sometimes diseases will travel between roots from an infected tree to another tree. Dutch elm disease and oak wilt are examples of diseases that can spread through a root system.

Article by FCFCDB

Nature Notes for 4/14/2013