What is a Tree Protection Zone
The Tree Protection Zone (TPZ) is the means by which we protect trees on development sites and should protect both roots and crown spread simultaneously. The TPZ should be considered as sacrosanct, that is it should be isolated from any construction disturbance unless previously agreed with the Project Arborist. The dimensions of the TPZ are determined from the Diameter of the Tree at Breast Height (DBH)
What is the Structural Root Zone
The Structural Root Zone (SRZ) is an area considered essential for tree stability: loss of roots in this area are likely to cause the tree to become unstable in the ground. The SRZ should only be calculated if major disturbance of the TPZ is being considered. The dimensions of the SRZ are determined from the Diameter of the Tree taken above the root flare.