Why does this topic matter?

• The survival of urban trees depends critically on the health of the roots.
• Roots and shoots are linked through a kind of circulatory system: what hurts the one, hurts the other.
• Roots supply water and nutrients to the shoots, and get back sugar and other compounds they need to grow and survive.
• Roots also store food, synthesize needed compounds, and provide support.
• Most tree roots lie in the top 6-18" of the soil, and usually extend well beyond the canopy edge.  About 1 of every 5 species (e.g., red oak) typically has a "heartroot" structure, with roots going deeper.  Very few species are actually taprooted.  The actual root structure of a particular tree is highly influenced by local site conditions.

• When something cuts the roots, stops them from growing, or prevents them from breathing, it causes damage and threatens the life of the tree.
• Common urban activities that often damage roots include:

• building construction
• road widening
• utilities repair
• sidewalk replacement
• lawn parking
• patio or paving installation
• grade change
• stockpiling materials on the ground
 
• Damage to the root system can often be detected from discoloration, reduced size, or death of part or all of the tree’s crown.

 

                                                    Root damage on red oak leading to stem failure

• Loss of support.  When the big buttress roots are cut close to the tree, the tree has no support on that side and is prone to windfall.
• Loss of water.  Cutting the roots that supply water makes the tree vulnerable to drought, and also to pests that attack water-stressed trees.
• Loss of nutrients.  Roots must grow to take up many nutrients, and when the soil is compacted by traffic or other loads, roots are unable to penetrate it.
• Loss of food. Roots, like people, must be able to breathe to use the food they get from the leaves. When roots are smothered, they die from starvation.

• Fence off the ground underneath the tree’s crown before construction begins. If traffic must go through that area, first put down 6-12" of gravel or coarse mulch.
• Work with your utility company to tunnel under tree roots, when appropriate.
• When replacing sidewalks, lay them around (or up and over) the roots of older trees.
• Don’t raise the soil grade over roots more than a few inches without special precautions.
• Set paving blocks in sand, and don’t mortar them together.
• Mulch wide and 2-6" deep, especially younger trees trying to establish their roots.

ISA.  1999.  "Avoiding Tree Damage During Construction"  Champaign IL: International Society of Arboriculture.  For other information, advice and help on this topic, call offices of your State Urban Forestry Coordinator or University Extension service, or visit urban forestry websites.