Root systems are not perfect circles, they adapt to hardscapes such as structures on deep footings or engineered roads. Simply put, to estimate root system loss, you must know where the roots are.
On most site plans, root systems are shown as perfect circles. This method is unscientific and misleading. The example shows a root zone drawn as a perfect circle, where roots are shown to extend under buildings and hardscapes.
The result is that root system loss is depicted as just 15%. At this low level of root loss, a tree might survive.
When boundaries to root growth are correctly outlined, the Tree Matrix Root Plotter depicts a more accurate root growth pattern. Because of the influence of hardscapes in this example, the Root Plotter predicts the same disruption would damage 38% of the root zone.
Tree Matrix Root Plotter predicts a 38% root loss, which can be highly impactful to most trees.
Our algorithm is derived from over 35 years of tree preservation experience, peer reviews and the most modern research into our 5 factor algorithm. It is validated by world reknowned experts.
The Tree Matrix algorithm has been vetted by leading researchers and experts in the field of arboriculture. While more research is needed in areas such as root growth patterns and the accumulated impact of root loss, the formula represents the most contemporary understanding of construction impacts on trees. The result is a highly accurate assessment of how construction will impact an existing tree.
The root plotter depicts the most accurate root growth patterns based on physical barriers to root expansion. In order to accomplish this the user must identify these barriers.
Critical root zone (CRZ) is a term often used to identify the anticipated full extent of a tree’s root system. At Tree Matrix, we depict this zone by using a formula derived from research published by Susan D. Day, et al. (Arboriculture & Urban Forestry, 2010. 36(4):149-159). We feel that this formula provides the best depiction of root expansion for trees of many sizes and species.
Our ‘Root Plotter’ software depicts the CRZ based on this formula, and in response to boundaries that are likely to deflect root growth. Existing boundaries include structures on deep footings (>30”depth) such as buildings, retaining or privacy walls, or roadways with substrates compacted to a Proctor density of 95%, or greater. If a user does not agree with our depiction, they can manually adjust the CRZ. Adjustments can be made to accommodate for trees on slopes, the existence of features such as wet soils or to reflect species characteristics.
Once trees and their characteristics are added, and the limits of disturbance shown, a survival score is produced. The rooting area that remains is then determined to be the Tree Protection Zone (TPZ). The advantage of the Tree Matrix approach is that we provide a TPZ with a survival score. This is the level of certainty that a practitioner needs in order to then prepare a tree preservation plan.
At its core, tree preservation relies on determining the likelihood that a tree will survive the impacts of construction or development. Unless we can best approximate the spread of a tree’s root system, it is difficult to determine whether a tree will survive root loss. And while nuances of root expansion cannot be anticipated, our formula is conservative, sound and widely accepted by tree protection practitioners.
A tree protection zone (TPZ) is defined within the most current industry best management practices (BMP) as a “defined area within which certain activities are prohibited or restricted to prevent or minimize potential injury to designated trees, especially during construction or development.” Within these BMP’s, there are three different definitions of a TPZ.
At Tree Matrix, we feel that all of these definitions are unscientific and fall well short of what is needed in tree preservation – a calculation of tree survival based on a host of parameters that will determine tree survival. We define the TPZ as the area of root system that is preserved and which is based on the development plans, and in consultation with the project arborist. The difference between Tree Matrix and the BMP’s is that we provide users with a percent likelihood of survival for each tree impacted.
Root protection areas (RPA) are defined in the British Standards (BS-5837) only. They read quite similar to the CRZ definition.
Structural root zone (SRZ) refers to the plate like area around a tree containing the larger diameter roots whose function includes both structural support and transportation of water and photosynthates. This zone is also called the ‘root plate’ or ‘zone of rapid taper.’
We add quantitative definition and survival percentages to the CRZ, TPZ and SRZ because this approach adds certainty to tree preservation planning! Tree preservation, in concert with tree planting, are the foundations of urban forest canopy enhancement. In order to help stem the worst impacts of climate change, we must protect larger, existing trees where much of the pollution is produced. That is in the urban and suburban settings. The arboricultural industry should not limit tree preservation planning only to those with decades of experience but should expand the ranks of practitioners by providing technology to produce tree preservation plans more accurately. Tree Matrix provides this technology.
The Tree Matrix algorithm uses five parameters that affect the long-term survivability of trees following construction. The formula produces a score as a percent likelihood of survival. The range is from 0-100%. Here are the likely results given a particular survival score:
The Tree Matrix algorithm uses five parameters that affect the long-term survivability of trees following construction. The formula produces a score as a percent likelihood of survival. The range is from 0-100%. Here are the likely results given a particular survival score:
0-59% Survival scores in this range suggest that the tree will not survive the typical 3-5-year recovery period after impact. In this range, it is best to remove the tree.
60-64% Survival scores within this range have a low to moderate chance of survival. Pre- and post-construction treatments are essential to best insure survival.
65-69% Survival scores within this range suggest that survival is possible with pre- and post-construction treatments. Supplemental irrigation and insect and disease control will be required.
70-80% Scores in this range suggest that survival is likely, but that pre- and post-construction treatments will be necessary. Supplemental irrigation and insect and disease control is highly recommended.
81-90%, Scores in this range are good, and suggest that survival is likely. Irrigation may be applied based on the amount of natural rainfall, and the general water needs of the specific tree impacted. A permanent irrigation system would not be required. Insect and disease monitoring and control are beneficial.
91-100%, Scores in this range are excellent. It suggests that the tree should not display any signs of stress, or a loss of vigor. A permanent irrigation system would not be required. Insect and disease monitoring and control are beneficial, but not necessary.
Four of the five factors can be altered to increase survivability likelihood. Root zone loss can be reduced, tree condition can be improved, the season of impact altered and the number of 'sides' impacted around the tree can be adjusted.
Users can alter 4 of the 5 parameters used in our formula in order to increase the likelihood of tree survival. The percentage of roots lost can be decreased, season of impact can be directed to the dormant season, the tree’s condition can be improved prior to root pruning, and, finally, the number of sides impacted can be kept to a minimum. All options should be considered in the user’s attempt to reach a survival score of at least 70%. Trees with survival scores below 70% may survive, but it will require a higher degree of pre- and post-construction treatments.
