Keep Trees Out of the Danger Zone

Have you even seen those little fenced-in areas around trees or palms that are on sites that have or will soon have construction? These little fenced-in areas are supposed to protect the critical root zones of trees or palms from construction activities. 

While the American National Standard for Tree Care Operations and its multiple parts are written into the ordinances of most if not all of our local municipalities, these standards are often ignored by or not closely followed by many if not most municipalities and building departments. The nine standards, better known as ANSI A300, address specific areas of tree care including pruning, root management, tree risk assessment and integrated pest management, and are periodically updated by the pertinent ANSI A300 committees to align with current arboricultural and safety knowledge.

So, what is a critical root zone (CRZ)? This is an area of the root zone around the trunk of the tree, sometimes called the root plate, that cannot be disturbed. No construction activity, no root or soil compaction, no digging, no storage of equipment or supplies, no portable toilet and no parking can occur within this CRZ. That is, if you don’t want the tree or palm to die.

How is the CRZ determined? The municipal arborist or a commercial arborist determines the size of the CRZ. Now there are many different formulas that tell how to determine the size of the CRZ, which typically are a multiple of the diameter at breast height (DBH) of the trunk which is measured at 4.5 feet above grade. This multiple can range from 1 foot of CRZ per 1 inch of DBH up to several feet of CRZ per 1 inch of DBH. You can find references that define the CRZ from the trunk up to the outer edge of the tree canopy. At the end of the day, the CRZ should be based upon the arborist’s knowledge of that tree species, the maturity of the tree, its condition and age, and knowledge of the site conditions before any demolition has taken place. 

Take a look at the photo of the two live oak trees above. Only one of the trees in the photo has any kind of fencing around the trunk. This pitifully constructed fence has some orange plastic fencing attached to it that is already falling down. It is barely a few feet beyond the trunk, and there is absolutely no fencing around the trunk on the other side of the large permanent barrier which is just another fence lined with black fabric. The second live oak tree has no temporary fencing around the CRZ at all.

I was not involved with this project and have never walked the site, but given the sizes of these live oak trees I would put the CRZ to be about an 18-foot radius around the trunk. Who in that municipality reviewed and approved those imaginary tree protection barriers? Obviously, this municipality that is a designated Tree City USA doesn’t follow its own ordinances. These trees have been sentenced to a very slow death.

What does this lack of a sufficiently designated CRZ cause? Slow tree death! Look at the second photo; the one with the two slash pines with the yellowing foliage and small branch die-back. These two pine trees are rapidly dying because of soil compaction and root damage. A public works project in another municipality was just completed next to these pines that never had a CRZ barrier constructed around them so the public works constructors used the CRZ to park equipment and store sand. Now I would expect that this municipality had building inspectors come out to review all the pipes and stuff dug into the ground nearby. It seems the tree protection barrier was certainly not inspected.

Slash pines are very susceptible to soil compaction and disturbance of their root plates. That is why they are becoming rare in our area. They will die much faster than the two live oak trees in the other photo.

The two live oak trees will take some time to die. Live oak trees are a tough resilient species and can take several years to outright drop dead. While our municipalities seem to be allowing the removal of a very large percentage of our mature tree canopy for “progress,” we need to look at the other side of the coin here.

The mature trees that get damaged and stressed due to construction activities often survive long enough to become a part of the now much smaller landscape of a new project or residence. These trees, which eventually die, will have to be removed by the new property owners, at their own expense. They will have to pay for an arborist report, the tree removal permit, the actual tree removal and possibly be required to plant new trees to replace the lost canopy, all because the tree had not been properly cared for during the construction process. Who was responsible for this tree death? 

Jeff Shimonski is an ISA-certified arborist municipal specialist and a retired director of horticulture at Parrot Jungle. Contact him at jeff@tropicaldesigns.com