Some counties or cities may require that a tree preservation plan be part of a construction project. Fines may be incurred if the plan is not in accordance with a municipality's requirements.

Tree Preservation is the process in which the tree's Critical Root Zone (CRZ) are protected from potential damage that can occur during the construction phase, such as driving over the tree's root system with heavy machinery, root damage from tearing, and compaction of the soil.

Critical Root Zone (CRZ)

Mature trees can suffer devastating effects if preservation is not performed to protect their root systems.

Because of their extensive root systems, mature trees are more likely to be irreversibly damaged.

The root system of the tree is not the same size as the crown or spread of a tree, for example: a 25" DBH (Diameter at Breast Height) tree has a CRZ of 37.5 feet of area; that should not be disturbed. CRZ may be calculated differently according to some municipalities, always check the requirements.

When grading occurs, the fibrous roots of the trees are damaged by ripping or tearing. This decreases the tree's oxygen intake and changes the water table.

When grading is necessary it is recommended that the tree's roots are pruned.

Root pruning consists of using a special high velocity air tool to remove the dirt. The dirt around the tree's base and within the CRZ is airspaded. The roots are then selectively hand pruned and cut back to prevent tearing of the root systems during grading. Hand pruning will allow for clean cuts rather than tearing of the roots.

The tree preservation plan should include how grading will affect the tree and what procedures should be taken.

Airspading was performed in order to access the roots of the tree. The rooots were hand pruned to avoid ripping or tearing during construction.

Protective Fencing

One of the most important part of protecting the CRZ is to ensure that proper fencing is installed. The fencing serves as a boundary line indicating "TREE PRESERVATION AREA."

Fencing also deters heavy trucks or machinery from entering a critical zone area. Signs should be properly posted so that contractors are aware and to "KEEP OUT".  Certain types of fencing should be used to secure the signs.

Prevent Soil Compaction

Soil compaction can occur when heavy machinery compresses the soil, reducing a tree's oxygen intake and decreases pore space water.

Soil compaction commonly occurs on construction sites and is one of the main causes of decline in the health of trees. 

To avoid soil compaction, proper fencing should be installed with signage to warn that the CRZ is in a protection zone. Where this can not be avoided, wood chips, compaction mats should be installed.

Radial Trenching

If soils become heavily compacted, it may require radial trenching to facilitate natural root growth.

After Care

After completion of a construction project an after care program for the trees should be followed. An after care program usually consists of plant health care such as fertilization and root or soil treatment as well as monitoring.

Plant health care will benefit the tree to increase the tree's vitality and boost the tree's system.