To understand how construction harms trees, we have to dispel a common myth about how roots grow. Many people picture a tree’s root system as a mirror image of its canopy—a deep, carrot-like structure reaching far into the earth. In reality, a tree’s root system looks much more like a pancake.
Because tree roots require oxygen to survive, about 90% of a tree’s fine, water-absorbing feeder roots are located in the top 12 to 18 inches of soil. Furthermore, these roots stretch out horizontally, often extending two to three times the width of the tree’s drip line (the outer edge of the branches). This wide, shallow, and highly vulnerable area is known as the Critical Root Zone (CRZ).
When home additions are built, or landscaping is aggressively overhauled, rubber-tracked CAT excavators, skid steers, and heavy material delivery trucks frequently park or drive over this CRZ. This causes two major, life-threatening issues for the tree:
Severe Soil Compaction: Soil is not just dirt; a healthy soil profile consists of about 50% solid particles and 50% pore space (filled with air and water). The heavy weight of machinery literally crushes these macropores, increasing the soil’s bulk density. Without these microscopic air pockets, oxygen can no longer reach the root system, and carbon dioxide cannot escape. The roots essentially asphyxiate, leading to rapid canopy decline, dieback, and eventual tree death.
Root Severing: Trenching for new utilities, sprinkler irrigation lines, or retaining walls cuts directly through major structural roots. Severing just one major root can instantly remove 20-30% of the tree’s water and nutrient supply, while severely compromising its physical anchoring, turning a healthy tree into an immediate fall hazard.
According to the ANSI A300 Part 5 standards for Management of Trees and Shrubs During Construction, protecting a tree requires establishing a Tree Protection Zone (TPZ) long before a single shovel hits the dirt. This involves erecting highly visible physical barriers, like chain-link fencing, around the CRZ to keep machinery, foot traffic, and chemical runoff (like concrete washout) far away from the root system.
If trenching is absolutely unavoidable, modern arboriculture offers alternatives. Techniques like air spading (using high-velocity air to blow away dirt without harming roots) or directional boring (drilling utility lines underneath the root system) can save the tree’s structural integrity.
If your property is undergoing development, or if you are seeing signs of decline on a post-construction lot, the team at Arborman Tree Care can help develop a root remediation plan. Contact us at 208.286.6875 or visit arbormantreecare.net.
Fast emergency response available anytime for emergency tree services.
Fill out the form below and we’ll take care Of the rest.
