As you look at big, majestic trees, realize that you’re only viewing half of the tree. The rest is below ground – the root system. Without the below ground portion, the above ground beauty that we enjoy so much couldn’t exist. So, don’t be surprised when our arborist recommends a root excavation.
Contrary to popular belief, most trees don’t have a giant tap root that descend deeply into the ground. Rather, most roots are concentrated within the first few feet below the surface. And they spread out to the dripline (the extreme edge of the crown) or beyond. The job of some roots is to stabilize the tree while others have the task of seeking out and absorbing water and nutrients.
Roots share the subsurface world with a host of microbial organisms. Most of these are beneficial but a few are not. The latter can be lethal. I’m thinking specifically of fungi that cause root rot. If left unchecked, these microscopic organisms can, eventually, cause the tree to topple.
Beneficial soil borne organisms range in size from earthworms to microscopic fungi, called mycorrhizae, that colonize the roots, extending their reach. Worm waste, called castings, is rich in organic matter, which is returned to the soil. It’s like nature’s fertilizer. Some organic gardeners buy worms to raise in a controlled environment. They harvest the castings and work them into the soil around the base of their plants to provide natural fertilizer. It’s called vermiculture.
As fungi, mycorrhizae have no chlorophyl to manufacture food. Also, they’re below ground and have no access to the sun, needed to manufacture food by photosynthesis. So, they enter into a symbiotic relationship with the roots. The mycorrhizae extend the length of the roots and help them find water and nutrients and the tree allows them to partake of a portion of the food stored in the roots.
Much of the time when arborists diagnose stress in the crown, it’s associated with a root problem. The cause is mechanical, or abiotic. Girdling root is by far the major culprit. This condition is caused by the roots outgrowing the nursery pot or the planter not checking the roots to make sure they’re growing outward instead of around the tree. It’s very visible as one root grows over another, virtually choking it to death.
A girdling root can be corrected by a simple surgical procedure. However, it used to be more time consuming than it is today. We used to have to dig into the root zone with a trowel, being careful not to sever the many feeder roots. Today, we use a device called an air spade. This tool uses high pressure air to blow the soil on to a tarp, leaving the root structure intact. The soil is then put back in place after the procedure.