Magnolia Avenue Oak Canopy

Magnolia Avenue Oak Canopy Needs Special Care

Residents along Magnolia Avenue have noticed that since the hurricanes of 2004 the live oak canopy has thinned. In actuality the tree canopy had been thinning for a number of years but became most noticeable after the slow recovery from the partial defoliation caused by the hurricanes. In 2005 the City of St. Augustine gave a small grant to the Magnolia Avenue Neighborhood Association to hire an arborist to investigate the problems and make recommendations. I was hired. After examining each of the 60 trees on the avenue, I made the following report:

Beautiful but mis-named Magnolia Avenue, St. Augustine’s most photographed and impressive street. The 60 live oaks that are between 80 and 100 years old form a canopy over the street. Photo courtesy of Lydia Williams (lwilliams@se.rr.com)

Beautiful but mis-named Magnolia Avenue, St. Augustine’s most photographed and impressive street. The 60 live oaks that are between 80 and 100 years old form a canopy over the street. Photo courtesy of Lydia Williams (lwilliams@se.rr.com)

 

 

Report on Magnolia Avenue Live Oak Canopy

October 16, 2005

Magnolia Avenue in St. Augustine is one of the most beautiful streets in the United States because of the arching live oak canopy and Spanish moss. But all the trees are not in good condition. Near misses by hurricanes last year exacerbated the problem by removing a significant amount of foliage from many trees. Other problems include:

  • Restricted space for roots
  • Soil with low organic matter, high compaction and poor aeration
  • Conflicts with infrastructure such as curbs, sidewalks and streets
  • Competition from turf and other landscape plantings
  • Construction near some the trees
  • Improper pruning by untrained individuals

Each problem by itself is normally not enough to damage a mature live oak. But multiple problems can gradually wear down even the healthiest live oak causing branch dieback, sparse foliage and a general weakened condition which then makes the trees more susceptible to other environmental stresses. Mature trees are more susceptible to the negative effects of these problems. Most of the problems observed are man-made and consequently can be fixed if there is a will to sustain this beautiful street.

Introduction

Background & Assignment

Recently some residents have observed a decline in the amount of foliage of the oak trees along Magnolia Avenue and have expressed their concern to the city. A grant was obtained to hire an ISA [1] Certified Arborist with experience in tree health and maintenance issues. This arborist would assess each tree and make recommendations that would improve the condition and health of the trees. Under that grant Richard French of the Magnolia Avenue Neighborhood Group requested proposals for the work and subsequently contracted me. The assignment was to assess the condition of the 61 oak trees on Magnolia Avenue and make recommendations on treatments that can improve or sustain the health of the trees on this very important street in St. Augustine.  Of the 61 trees, 59 are live oak and the remaining two are water oak and laurel oak respectively. Live oak are by far superior trees to the water oak and laurel oak.

Data Collection

Each tree was evaluated according to current procedures used by certified arborists who are trained in the latest pruning techniques, hazard tree assessment and hazard abatement. Each tree has an identification number, is identified by species and diameter (DBH), is evaluated for problems observed, and finally treatment or mitigation recommendations are made for each tree.

Purpose & Use of the Report

This report is for the use of city officials and staff, residents living along Magnolia Avenue, residents of St. Augustine and anyone who is interested in trees. The purpose of this report is to document the health and condition of each tree and make recommendations, which are based on the latest university research about trees and tree health. Recommendations are made in good faith as the best procedures to follow. However, it is up to the city officials and residents to decide which recommendations they wish to follow.

Observations

The Process of Aging in Trees

Trees don’t live forever. But our own Southern live oak (Quercus virginiana) comes as close as any tree to being nearly immortal with the average age well over 100 years and some specimens living over 400 years or more. Aging trees have to constantly contend with limited resources such as inadequate root space, competition from other organisms for water, nutrients and sunlight, damage to roots to reset a raised curb or install a sidewalk, and the careless removal of food-making foliage and stored carbohydrates by improper pruning. Research [2] shows that photosynthesis, the important biological process of manufacturing food, decreases as a tree ages. Furthermore, as a tree ages it begins uses a higher percentage of the food it manufactures just to respire (stay alive). Urban heat conditions also increase tree respiration. In other words less food is generated for the amount of living tissue maintained by the aging tree.Further complicating the situation, the soil becomes “mined out” of available essential elements and organic matter over time. The tree’s ability to colonize new soil spaces with its root system becomes limited. Other processes become more complex as a tree grows larger and becomes older. Most notably the efficiency to conduct water and nutrients along the transport path from the absorbing roots all the way up to the growing tips of branches is reduced by about 50%. 

Tree Root Growth

Understanding tree root growth is important if we are to maintain healthy, long-living trees in our urban environment. There is a common misperception among people who are unfamiliar with recent research about tree growth and physiology. This misperception is tree roots grow downward and only out as far as the dripline (edge of the canopy). But we now know this is not the case. Tree roots grow outward from the tree often as far as the tree is tall which can extend out two or three times the diameter of the canopy, space permitting. Tree roots also grow mainly in the upper 18 to 24 inches of soil where the oxygen content of the soil is higher. Roots require oxygen to live. Roots are mainly shallow and roots extend far from the trunk outside the canopy when adequate soil space is available.

Tree and Site Problems Observed

Field DataProblems observed in the 61 trees. Each tree usually had two to four problems documented.

dead branches                          89%
previous bad pruning                   34%
vines climbing on trees                 34%
restricted roots                        25%
rubbing branches                       15%
lifting curb                              15%
decay                                    14%
competition from nearby plants        13%
recent construction damage             3%
fill soil added around trunk              3%

Root Restriction

Root restriction is a common problem for many of  the trees along Magnolia Avenue Tree roots are limited in area where they can grow. Many of the trees are much like a containerized plant that has overgrown its container. We are not able to repot the plant in this case but we can revitalize the root area.

Root-Infrastructure Conflicts

Furthermore, construction of sidewalks, driveways and curbs along the street has in all likelihood been done without regard to root protection techniques.  Standard construction and repair techniques involve cutting offending roots that are lifting sidewalks, driveways and curbing. These techniques are not only harmful because they cut destroy large portions of a root system and allow and entry point for decay organisms, but also cutting a large root close to the trunk can make a tree unstable. Alternative methods of working around root-hardscape problems are available [3] and should be implemented whenever street or driveway repair or construction is done.        

Poor Pruning

Another problem is the lack of proper pruning used by city crews and tree services hired by homeowners on the Magnolia Avenue trees. Improper pruning cuts such as heading cuts have been made. These cuts are detrimental to tree health and structural strength. Also, dead branches which should be removed have not been removed. Mature trees require regular monitoring for dead wood that should be removed before it falls. Dead branches can be hazardous. I heard that a city pruning crew worked on Magnolia Avenue in August or September, yet I still see lots of dead branches that should be removed And I see some other recent (fresh) cuts that puzzle me as to the reason they were made. I also see many trees that have been over-lifted through the years by removing interior branches. Over-lifting, otherwise known as lion-tailing, reduces branch girth growth and puts more weight out at the end of a branch making branch failure more likely.The tree industry has established pruning standards [4] that are easy to understand and easy to follow. Allowing untrained people to work on these trees including city crews and tree services without a certified arborist on the staff has been detrimental to tree health and structure. Letting untrained people to prune these trees should no longer be permitted.       

Competing Plants

Another problem observed is the competition in the limited root space with ornamental plants. Not only do these herbaceous ornamental plants compete for resources such as water, nutrition and space but also the soil in these plant beds is kept moist due to supplemental irrigation. This extra moisture can cause root rot problems for the trees especially older trees that are more susceptible to environmental stresses. There are even some raised planting beds with supplemental irrigation right next to the tree trunks. If we really want to protect these trees, planting close to the trunks should be prohibited.

Vines

About 34% of the trees have vines growing up the trunks and into the canopy. On a few of the trees the vines have climbed into the canopy and are beginning to shade the tree foliage. In other cases the vines are thick enough to cover trunk and branch decay problems that may otherwise be evident by inspection from the ground. Vines also increase the moisture level on the bark which is generally not a problem except for stressed, mature trees. Also, vines can compete with trees for limited root space. Vines should be removed.

Fill Soil over Root Flare

Trees should have their root flare, the wide area at the bottom of the trunk exposed. A walk in a natural forest will show that all trees growing in their native habitat have their root flares exposed. Often in urban areas fill soil is added to the base of trees and the root flare is covered making the root flare susceptible to decay. Once root flares decay, the tree can become unstable and can fall over because the roots are no longer supporting it. Fill soil and raised planting beds should be removed. 

Decay

All mature trees have some decay. It is part of aging. It is important to determine how much decay is present and where is the decay located. Sometimes we can see much of the decay. Other times the decay is partially or completely hidden inside the tree. Dead branches should be removed regularly and decay should be monitored.

Recommendations 

Therapy for Old TreesThere are four primary treatments for aging trees. Most are common sense but should be applied and monitored by a professional arborist.

  1. Soil:  Maintain a supply of organic matter which is essential for soil health and mature tree health. Organic mulch will improve aeration, drainage and alleviate compaction and restricted root areas.
  2. Space:  Remove other plants that may be interfering with old trees. Old trees are less able than young trees to effectively compete with surrounding landscape plants. Mulching to gain separation distance and maintaining a clear zone around the trunk is important for old trees.
  3. Improve Tree Structure:  Old trees are burdened by their mass, reach and size. Reduction of tree reach can reduce the risk of structural failure and improve transport path problems. Proper and very careful pruning in small doses is essential. Removing too much leaf surface and stored carbohydrates in sapwood will weaken the tree. Structural problems should be addressed by trained arborists not untrained tree cutters who know nothing about tree physiology and maintenance requirements.
  4. Minimize Stress: Irrigate old trees during periods of drought. Avoid flooding conditions and injury to trunks, branches and roots through careless construction, curb restoration and improper pruning cuts. And finally don’t dump fertilizer on old trees like is done on young trees and lawns.

To accomplish the above therapies for the oak trees on Magnolia Avenue, I recommend the following:

Mulch

Organic mulch without a weed mat should be placed over as wide an area as possible beneath the canopy of each tree. Mulch should be placed up to six inches from the trunk but should not touch the trunk. Mulch should be from two to four inches deep and be supplemented only as needed.

Mulch is probably the most useful and least expensive treatment for tree roots. The larger the mulched area the better. Mulch provides these benefits:

  • replenishes organic matter to the soil
  • improves the microbial activity in the root zone
  • helps aerate the soil
  • breaks down to provide slow release nutrition to the trees
  • buffers the soil from temperature extremes
  • retains soil moisture levels
  • provides a cushion against compaction
  • suppresses weeds and other plants that can compete with the tree for water and nutrients

I recommend that the entire boulevard be mulched on both sides of the street. If such extensive mulching is not acceptable to those who want a lawn all the way to the street, then at a minimum a mulched area with a 15 ft. radius should be maintained around each tree. This mulching can be laid down over the soil and does not require bricks or other hardscape. I do not recommend hardscape of any kind that is inserted into the soil because root damage can occur. Anyone wanting to use hardscape such as edging or concrete curbing commonly used in landscapes, care should be made not to damage surface roots during installation. The cost to transport screened and composted yard waste mulch is approximately $300 to $400 depending on the amount used. If city trucks could be used and county yard waste, the cost could be reduced to near zero.

Soil Aeration and Root Flare Excavation

Arboriculture has some new tools available to available to help soil aeration. One such device is the Air Spade which uses high velocity compressed air to inject air into the soil and also to move soil away from roots for inspection. Areas of compressed soil can be loosened and aerated without harming roots. Root flares that have fill soil on them can be inspected for decay after the excess fill soil has been removed with the Air Spade. I have selected 15 trees for basal flare evaluation which will take approximately one day. Compressor rental for one day is $100. I will donate my time at one third my normal rate which would be $200. Soil aeration and root flare excavation would cost $300.

Growth Regulator Treatments

As a supplement to mulching and soil aeration treatment, we should consider tree growth regulators. There is a product on the market that has been shown to be beneficial in stimulating root growth. This product is not a fertilizer but a plant growth regulator– Cambistat (Paclobutrazol) which was originally used by utility companies to retard tree growth near power lines. Over time it was observed that while top growth slowed, root growth was enhanced. Now Cambistat is used for stimulating root growth on stressed trees.The cost to treat a 30 inch diameter live oak is approximately $200. I suggest we select five trees that could benefit from the Cambistat treatment and treat them. If a positive response is observed during the next two years, we could apply for additional funding to make more treatments.

Decay Evaluation

A Resistograph allows the arborist to examine the extent of decay present in an accessible portion of the tree. Another simple tool, a mallet, can be used to locate hidden decayed areas before the Resistograph is used to measure the decay. I have selected several trees for Resistograph examination. It is estimated the Resistograph examination of four trees at ground level would take one to two hours. I would donate my time and equipment at no charge for this diagnostic procedure. I also recommend that a self-motorized or towable lift be used to examine branches that overhang the street. I estimate a mid-level branch examination for decay would take four hours plus the rental cost of the lift. The estimated cost for a mid-level branch examination over the street would be $300 to $400. If the city has a lift that could be used, then the $200 rental cost could be eliminated.

Fertilization

Generally older trees do not need supplemental fertilization. In fact research has demonstrated again and again that over fertilization is harmful to trees, especially mature trees, making them more susceptible to insect pests and decay organisms. At this time fertilizer is not recommended and would be counter-productive. Future prescription for fertilization should only be made by knowledgeable arborists, especially those who are not selling a fertilizer treatment or regimen.

Limits of the Assignment 

I can only make recommendations based upon problems observed and known remedies. My recommendations are not unlike those of a physician who tells his or her patient that they should eat a low-fat diet, exercise regularly and stop smoking. The patient can adopt all the recommendation or some of them or can ignore them completely. And even if all the recommendations are followed, there are no guarantees that a person will live longer. We are working with percentages and odds. We know if we do certain things, our odds of living longer are increased. The same goes for my recommendations for the trees. There are no guarantees but we know the odds of tree longevity can be increased.

 Definitions 

Air Spade: A diagnostic tool which uses high velocity compressed air to excavate tree roots and root flares for decay, girdling roots and non-biodegradable straps and ropes that are sometimes left in place by tree installers. The Air Spade can also be used for non-invasive trenching or for soil aeration by making vertical aeration holes in compacted soil. The air stream will remove soil from roots without harming the roots.
Certified Arborist: An arborist who has met the qualification requirements of the International Society of Arboriculture, passed a comprehensive exam and maintained his or her certification current by taking the required number continuing education classes. Some certified arborists have more training and experience than others. Certification is a minimum standard.
Dead Branches: Every mature tree disposes of a branch from time to time. Occasional branch dieback is normal. Excessive branch dieback is a sign of root or other problems. In either case these dead branches should be removed periodically before decay and gravity cause them to fall. Mature trees in public areas with people or property within the dripline should be checked for dead branches annually.
Develop sprouts into branch structure: This restoration pruning procedure trains sprouts (epicormic growth) over a period of several years to become larger interior branches on a tree. This procedure is used on trees that have been over pruned or lion tailed to help restore the tree structure.
Diameter: refers to a measurement of a tree’s diameter made at approximately 4½ ft. above the ground. This measurement is also referred to as “diameter at breast height” and is abbreviated as DBH.
Dripline: the outer edge of a tree’s canopy
Epicormic Growth: Sprouts that form when a tree has lost excessive foliage or has been over-pruned. Epicormic growth is often a sign that is tree is stressed or declining.
Lion Tailed Trees: the removal of interior small branches from a larger branch leaving more foliage and branches out at the extreme end of the larger branch. This practice is done by unknowledgeable pruners under the guise of cleaning the tree to reduce wind resistance and improve the appearance. But the practice actually increases the tree’s susceptibility to wind damage by forcing more weight out to the end of the branch. Also, the loss of interior branches decreases the rate of growth in girth of a branch further increasing the susceptibility to wind damage.
Poor Pruning Previously: Pruning procedures that do not follow ANSI A-300 Pruning Standards. Heading cuts, topping, lion tailing, stub cuts, flush cuts are all pruning cuts that are detrimental to tree health and structural integrity and should not be used.
Reduction Pruning: The process of pruning back a long branch by removing weight off the extremity and cutting back to another live branch which is at least 1/3 the diameter of the main branch. Reduction pruning can reduce failure risk and has a low negative impact on the tree
Root Plate: The distance around the trunk of a tree that is three times the diameter of the tree from the outer edge of the tree. See the diagram in Appendix A. Cutting, covering with fill or otherwise damaging the roots within the root plate can make the tree unstable and can also shorten the life of the tree by damaging the root system and allowing an entry point for decay organisms into the root.
Root Flare Exam: The process of removing soil from the base of a tree trunk in a non-invasive manner to assess the root flare for decay or girdling roots. An Air Spade excavation device is usually used for this type of exam.
Resistograph: A diagnostic device made in Germany that allows the arborist to determine the location and size of decay inside a tree trunk or branch. The technique is slightly invasive but worthwhile when a potentially high risk tree is being evaluated for decay.
Thinning or Sparse Foliage: Foliage that is less abundant on a tree than the foliage of nearby healthy trees of the same species. Thinning or sparse foliage is a sign of decline or other abiotic problems.
Topped Trees: hat-racking, stag heading, de-horning, lopping, rounding over, shearing all refer to the damaging practice of cutting a branch back to a stub without regard to the location of other branches or buds. The practice causes exuberant sprout growth. Sprouts are weakly attached and often break off. The stub often decays which increases susceptibility to storm damage.

Endnotes

[1] International Society of Arboriculture, P.O. Box 3129, Champaign, IL 61826, www.isa-arbor.com, 888-472-8733.

[2] Managing Tree Aging by Dr. Kim Coder, professor Univ. of George, Arborist News, June 2005.

[3] Reducing Infrastructure Damage By Tree Roots: A compendium of Strategies, L.R. Costello and K.S. Jones, Western Chapter of the International Society of Arboriculture, 2003.

[4] ANSI A300 Part 1 – 2001  Pruning, American National Standard for Tree Care Operations, Tree Shrub, and Other Woody Plant Maintenance – Standard Practices (Pruning), American National Standards Institute, Inc., 1819 L St. NW, Washington, D.C. 20036