Trick or Treat - Below Ground Tree Care
by Liz Riley, Alamance Community College
Halloween is right around the corner and trick-or-treating will take place on many of the streets in North Carolina soon. Have you ever paid attention to the health and structure of the tree canopies that line those streets throughout our communities? Of course you have, because you are all members of the NC Urban Forest Council! Now, let’s turn it upside down, have you ever thought about and envisioned the root system growing underground for those trees?
Roots are a vital plant organ and they directly impact the overall health of the tree. They anchor the plant in the soil and they uptake water and nutrients for plant growth. In order for roots to be healthy and continually provide adequate support to the tree, they need access to oxygen. Our soils in our communities can very easily become compacted due to the use of maintenance equipment, foot traffic, the addition of parking lots or sidewalks near the root zone, etc. and this leads to less available oxygen in the soil and stresses the trees. Root systems of the trees are underground and are unseen and this seems to lead many people to think they are not important. Luckily we are seeing more street trees planted in many communities, but unfortunately their root systems are not always set up for a bright and healthy future.
General rule of thumb for soil volume for a street tree planting is 2 cubic feet of soil is required to support each square foot of canopy area. We need to be thinking about mature tree size when designing an urban tree planting area and selecting tree species. If we really want an urban tree to provide ecosystem services to the community (such as shade, water quality, carbon storage, etc.), then we need to start supporting the trees with deeper soils or larger planting sites. There are site and design modifications that can be used in a project if below ground space is a limiting factor, such has root channels, elevated sidewalks, and structural soils. Below ground considerations should be part of the decision making process early in the design stages of a project.
If our root systems are not properly cared for, the beautiful canopies that line our communities will soon become street monsters with dying canopies that are dropping limbs and leading to the potential for failure on houses or power lines. We need to make sure that we share with our communities as they add more trees and the importance of also providing an adequate environment for their root systems!
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