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Maintenance Pruning of “The Senator” Live Oak

The following is a letter we wrote to a local arborist who is learning proper tree maintenance and was given the job to prune one of St. Augustine’s largest, oldest trees:

Dear JD:

At your request Danny Lippi, an ISA Board Certified Master Arborist, and I agreed to give you some guidance on the pruning and long term care of the well-known tree known as “The Senator,” a veteran live oak (Quercus virginiana). We visited the tree on several occasions to view the wound created by the branch drop and were present on August 28, 2017 on the day you and your crew were pruning.

First we’ll discuss the tree crown and then the tree roots. Most veteran trees like The Senator no longer grow vigorously but instead use much of their energy resources for more limited maintenance growth, for producing defensive chemicals against pathogens in the form of decay fungi and insect pests, and for root growth to locate and utilize soil resources. And the energy to do all these things comes from the leaves where carbohydrates are produced.

The carbohydrates are the fuel that maintains the tree. Loss of too many leaves though excessive pruning can harm a veteran tree more so than similar leaf loss would affect a younger more vigorous tree. Consequently all pruning should be done carefully to avoid too much leaf or crown loss. Experts often say a veteran tree should not have more than 10 percent of its foliage removed in one growing season or one year. This amount of foliage removal can vary depending upon tree health, tree safety and the reason for pruning.

We evaluate a tree’s condition in two ways. First there is the tree’s health and secondly there is the tree’s structural condition. Both are important and both are independent conditions. You can have a tree in very good health that has poor structure that will cause the tree to fall apart or fail. We’ve all seen a tree with green leaves that failed. Likewise you can have a tree with excellent structure but poor health.

The Senator’s health condition is very good which means the foliage is dense with good green color. The Senator’s structural condition is good to fair because of long sprawling branches, some with stress cracks or areas of decay. Areas of decay in an old tree are not unusual and usually not a reason to become overly concerned. It is important to consider the type of decay, its size and location on the trunk or branch. It is important to remember many trees do not die from poor health as they become very old. They die by falling apart to the point they become hazardous or become structurally damaged and have to be removed.

Another consideration is trees very gradually become smaller as they age by dropping branches somewhat randomly. We can assist the tree is this type of natural crown retrenchment by gradually shortening long sprawling limbs. This end weight branch reduction pruning technique helps the tree in three ways. First end weight branch reduction pruning reduces the leverage stress that long limbs produce on the trunk and crotches. Second, this pruning technique reduces vascular pathways which helps the tree cope with an aging, less efficient vascular system. Third, removing end weight instead of removing interior branches, as is the custom with many tree services in our area, increases tree wind resistance. Internal smaller branches provide a damping effect in the wind and help dissipate wind loads. Research at the University of Florida has demonstrated that removing interior and lower branches actually makes the tree more prone to failure. This type of pruning is also called “Lions Tailing” is also prohibited by ANSI A300 Pruning Standards, but unfortunately Lions Tailing is a practice that continues to be widespread by untrained tree cutters.

Danny and I are pleased to see you are following correct pruning procedures utilizing end weight branch reduction techniques and properly evaluating areas of decay or branch damage that can affect tree response to wind events.

Another area of concern for trees but one that receives little attention because it is hidden, is the root system. A tree depends on resources such as water, nutrients and mycorrhizal fungus webs that can only be provided by the root system. A large old tree such as The Senator has mined much of the available resources from its limited root space within the large but still restrictive open area within the parking lot of the motel. The tree roots are far ranging and extend out as far as the pavement on all sides of the tree. Sometimes roots will go under the asphalt pavement and care must be taken when repairing lifted area of driveway or sidewalks to avoid significant root damage. That is why an arborist with experience in root management techniques be consulted whenever any construction or repairs are made within the dripline of the tree. Actually care should be taken a distance from the trunk equal to one and a half times the distance to the dripline.

One way to provide new resources to the root zone of The Senator is through using organic mulch throughout the root zone out as far as the dripline instead of planting turf. Organic mulch such as mini-pine bark chips or wood chips especially those created by grinding up removed branches is the best mulch. The mulch should be placed directly onto the soil without the use of any weed mats which will defeat the purpose of the mulch. We want the mulch to slowly decompose and become organic matter in the soil. This organic matter helps the fungi, bacteria and arthropod biota in the soil which is so important for tree root health. The decomposing organic mulch also provides fertilizer for the tree as the organic material breaks down at a slow rate. Veteran trees do not need additional chemical fertilizer. Decomposing organic mulch is the best slow release fertilizer available. And if wood chip debris from pruning is used, it is free.

Another good reason to get rid of turf within the dripline of the tree is turf requires high levels of nitrogen fertilizer which is way too much fertilizer for veteran trees. It is like giving steroids to grandpa. And also some herbicides used to control weeds and keep the grass looking good are harmful to trees. One of these herbicides is metsulfuron, a common generic herbicide that is unfortunately widely used and has been found to cause problems with live oaks and some other tree species.

The Senator is no doubt one of the oldest and largest live oaks in St. Augustine. Its age is often a question of debate because tree trunk diameter, the common method of comparing tree size and approximate age, can vary significantly among trees because of soil conditions, moisture and other environmental factors that affect growth. Nevertheless, trunk diameter is a useful parameter for comparing trees. And by any measure The Senator is a very special tree.

It was a pleasure working with you on this pruning project of The Senator. If you or the motel owner have any questions about our observations or recommendations, please let us know.

Advanced Tree Care, Inc.
Chuck Lippi, president
ISA Board Certified Master Arborist #FL-0501B
ISA Tree Risk Assessment Qualification (TRAQ)
ASCA Registered Consulting Arborist #443