1. Tree Type
The user will choose from a list of hundreds of trees listed by Common name. The trees in our database are rated by their tolerance to root loss.
2. Tree Condition
Condition ratings can be obtained by one of several scales in use within the arboricultural industry. The International Society of Arboriculture (ISA) published an excellent scale in 1978 that still in use today (Journal of Arboriculture 4(11), November, 1978). Ratings within the PAE are to be: Excellent, Good, Good to Fair, Fair or Poor. Each is assigned a numerical value within the formula.
3. Season of root loss
The user will have to identify the season of impact based upon their geographical location. Impact is based upon climactic season when root loss occurs from root pruning, trenching, excavation or grading.
4. Critical Root zone (CRZ) Loss
The PAE calculates the square footage of CRZ, which is based upon the tree diameter and the resulting area of a circle.
Critical Root zone Loss Calculation
Once the CRZ is expressed, the user can manipulate the CRZ shape to account for existing boundaries that the user has identified on the site map.
Boundaries that can redirect root growth include buildings with full footings ( generally 30” of depth, or more), parking lots, retaining walls or privacy walls that are built on full foundational footings, roadways (with the exception of dirt roads that will allow for root expansion), and any driveway or walkway that has been built on a thick sub-base of material (18”, or greater) that could inhibit root growth. In some cases, when no boundaries exist that can redirect root expansion, then the CRZ can remain a circle.
Determining the exact dimensions of the CRZ may be initially challenging. However, with frequency of use, the dimensions will become increasingly recognizable. User should not be frustrated, or confused since even in the arboricultural profession there is not agreement as to what features redirect root growth. However, there is agreement as to what conditions attract root growth and those include soil that is not highly compacted, well aerated soils with good structure, and soils that contain adequate moisture.
Scientific Accuracy vs Conventional Wisdom
It is also conventional thinking that roots can extend 2-3 times beyond the limits of the tree drip line. TREE ROOTS ARE NOT RESTRICTED TO THE AREA UNDER THE DRIPLINE! This is a misconception, and one that must be dispelled. To help the user track the CRZ, the PAE will “dock” the original CRZ to the right of the screen and will keep track of the new CRZ as it is being manipulated. Ideally, the manipulated CRZ would equal the calculated amount, but in the urban and suburban environment the CRZ is rarely fully expressed. Do not try to force the CRZ to match that which was calculated. It is not unusual for a tree’s CRZ to be less than optimal. This is often why the tree condition may be lower than expected.
5. Root Quadrants
Root quadrants affected by root cutting: The user will enter this parameter from the drop down menu used for the other parameters. The first root pruning (or cut, excavation, etc.) will define the first “side” of impact. Any other cuts made in a 90 degree angle from the first, or parallel will be another side.
When a tree grows in a situation where one, or more, sides are restricted by boundaries such as roadways or walls, then this may be a situation where there are only “3” or “2” sides. The drop down menu accounts for these situations.