Who is Better Qualified to Opine on Root Damage, Civil Engineer or Certified Arborist?

I was retained by a defendant attorney to determine whether her client’s tree was responsible for lifting the adjacent civil sidewalk that resulted in a plaintiff trip and fall lawsuit.  Based on the photographs and tree species, White mulberry (Morus alba), I was fairly certain her client’s tree was responsible for the sidewalk damage.

The attorney retained me and requested a site inspection and tree root assessment.  I trenched adjacent to the sidewalk and within a short time, encountered a three-inch diameter root growing under the sidewalk.  Further excavation revealed a network of two to four-inch diameter roots that had grown under the sidewalk, lifting a sidewalk panel, creating a hazardous condition resulting in a trip and fall accident.

I informed the attorney that root encroachment from her client’s tree resulted in the sidewalk damage, she said her civil engineer expert claimed it impossible for a tree root to lift a concrete sidewalk.  I questioned the engineers knowledge and experience with trees, was the civil engineer a certified arborist or horticulturist?

Although the answer was no, she felt his qualification as a civil engineer was superior to my qualifications as a certified arborist, tree risk assessor qualified, registered consulting arborist and a college educated horticulturist.  Her dilemma was having two experts who disagreed and she requested I alter my opinion.

I told the attorney altering my opinion to suit her needs was unethical, and I removed myself from the case.

The common myth is trees have tap roots that grow straight down into the soil.  While this may occur in very deep, loam soils, the reality is most containerized nursery grown trees lose their tap root in the container.  Once planted in our poor Southern California soils, when the tap root encounters physical soil obstructions, such as rock, clay or hardpan, the tap root divides and grows multiple roots around the obstacle, forming a fibrous root system.  Tap root grows into fibrous root system.

Trees require a spreading root system to maintain structural stability.  Trees dissipate energy generated during a storm or wind event by transmitting leaf, limb and trunk movement down to the roots.  A spreading root system anchors the tree movement and dissipates the energy far more effectively than a single tap root system.

Most tree roots grow within the top 24-inches of the soil horizon. Roots in top 24″ of soil.  Over time, structural tree roots (2-inch diameter and greater) growing within a shallow soil adjacent to sidewalks, footings, foundations, walls or othersub-surface infrastructure may cause damage.

Just as a twig grows into a branch, and then a limb, roots increase in length and circumference.  Irrigation water, sewer or water service leaks increase subsoil moisture beneath sidewalks or garage slabs, creating a perfect environment for root growth.

Cracked garage slab

As the root circumference increased, it exerts pressure on the concrete slab or footing above the root.  Depending on the species, root diameter might increase 1/8-1/4” annually.

Within five to eight years, a small feeder root may grow to one-inch in diameter or greater.

 

Ficus root cracked the garage slab

The root growth may be compared to the action of a hydraulic jack, as the circumference increases, the upward pressure on the sidewalk or slab may crack and or eventually lift.  Concrete lifting may often occur at an expansion joint between concrete panels

Sidewalk lifted at expansion joint

 

 

 

 

Root network beneath sidewalk.

Roots seek out soil moisture, they can and will grow under walls, footings and garage slabs.  Roots are opportunistic, leaky plumbing, old cast iron sewer lateral or water services contribute to the soil moisture needed for roots to flourish. 

 

 

 

Sewer lateral root damage

Roots may infiltrate pvc, abs and cast-iron pipe through even the smallest of cracks or holes. 

Once inside, the roots expand in size and quantity, eventually completely clogging the utility.

If the tree crown has grown over a sidewalk or adjacent structure, it is a reasonable assumption structural roots (two-inch diameter and greater) have grown under the sidewalk, slab or footing.

Root growing under house footing

Planter areas confined by concrete pose one of the greatest risks for root damage.  City sidewalks often incorporate small, square planters within the sidewalk easement.

Roots lifting water meter and sidewalks

 

Confined planters quickly fill with structural roots, as well as damaging girdling root.  As the tree crown grows, so to do water absorbing feeder roots.  Over time, root mass and size increases, structural roots may begin to grow beneath concrete improvement while seeking out moisture.

Leaking water meter, high soil moisture, confined growing space.

The tree pictured above and to the right had a leaky water meter adjacent to the small sidewalk planter.  The leaky service provided idea soil moisture conditions for the roots to lift the water meter box, adjacent sidewalks and crack the curb and gutter.

Preventative measures to minimize root encroachment include a variety of root barrier methods.  All root barrier systems work best when the tree is installed.  Once roots have enlarged and matured, barrier mitigation is not successful.

In summary, our Southern California poor, shallow soils do not support deep tree tap root systems.  Most trees grow fibrous spreading root systems.  Structural roots emanating from the root collar extend to the edge of the tree crown, (drip line).  Most structural roots growing beneath sidewalks range from two to four inches in diameter, lifting sidewalk panels on average one-two inches. Trees growing in confined planters or adjacent to concrete, utilities or foundations may develop structural roots capable of lifting, cracking or damaging adjacent improvements.

Attorneys should select an expert based on the case criteria, not simply a title, license or certificate. Choose an expert most appropriate to address the cause of the problem and develop opinions based on sound, industry practices.

 

 

 

 

 

Finally, A Turf Block Driveway With Thriving Turf!

Rarely have I seen a successful turf block driveway.  Turf block, turf stone, turf pavers are systems installed as living turf driveway alternatives.  The material provides structural support via plastic or concrete cells that are filled with a soil media for turf installation.  The block is designed to support vehicular traffic on driveways while providing a green alternative to concrete or asphalt driveways.

Turf blocks have been used for decades, but rarely have I seen thriving  turf grass within the block.  Not because of the product, but usually due to turf establishment and failure issues.  Due to reduced soil root area, soil compaction, irrigation infiltration and damaged soil structure result in poor turf establishment.  Soil preparation, drainage and proper irrigation coverage and operation are required to grow turf inside of a turf block system.

Lastly, using vigorous, warm season turf grasses that spread by horizontal solons, rhizomes, and rooting improves the successful establishment of turf grass, such as the Tiff hybrid Bermuda grasses developed for sports fields. Cool season turfs including rye, bluegrass and turf type fescues are clumping turfs that do not spread horizontally, thereby limiting establishment and healthy growth.  Cool season grasses are more susceptible to leaf and soil borne diseases, are easily stressed during hot summer months, nor are they tolerant of vehicular and pedestrian traffic and compaction conditions.  

Tiff hybrid Bermuda is well established within the turf block

Trip, Slip and Fall Hazard: Hidden Depressions in Grade

Successful landscapes require:

  • Proper grading, drainage and amended soil.
  • An automatic irrigation system achieving 100% head to head coverage.
  • Properly installed, high quality plant material.

Each of these functions may require a specific type component, installed at a specific height or location to reduce the potential of creating a site hazard that may result in an accident.  In commercial applications, landscape plans usually include details and specifications dictating type of product and how it should be installed.

Many common landscape products may be improperly installed including:

  • Pop up heads may be incorrectly set to grade against a sidewalk.
  • Valve or drainage boxes set too high or low relative to finish grade.
  • Shrub head installed on a riser adjacent to concrete improvement.
  • Hidden, obscured depressions in grade due to substandard compaction, settlement and subsidence.

    Drainage box set too low.

Improper product selection or substandard installation practices may appear obvious.  A pop up sprinkler head set above the top of  adjacent concrete sidewalk creates a trip hazard.  A drainage structure set well below the turf grade creates a trip slip and fall hazard.  Selecting and installing a spray head on a rigid riser next to a pedestrian sidewalk is a sub-standard industry practice that creates a trip and fall hazard.

Spray head on a riser next to a sidewalk creates a trip hazard.

Not all landscape hazards are visible.  Turf areas may have grade depressions or holes that are hidden by overgrown turf grass.  Depending on the cause and time period, turf grass may completely hide the depth, location and size of the depression or hole, creating a hidden hazard.

A depression, rut or hole may result from several factors.  Repeated mowing on saturated turf may  create ruts.  Overwatering may cause irrigation or utility trench settlement.  A dead tree removed from a turf area may result in a future depression if the grade is not properly backfilled and compacted.

A seven inch deep hole hidden by turf grass.

Bermuda grass is a fast horizontal spreading turf-grass used in parks and recreation facilities throughout the country.  Unless regularly aerated and de-thatched, Bermuda grass in known to grow a  thick layer of thatch.  Over time, the thatch layer can increase the turf grade several inches above adjacent sidewalk and curbs.

The backfill in utility trenches installed across pre-existing turf may settle, creating a depression in the sub-grade.  The photo depicts the edge of a trench cut across an asphalt driveway, across a turf area.  The trench backfill eventually settled, creating a trench sub-grade depression hidden by the Bermuda grass.

Thatch, hidden depression and sanded turf.

The depression resulted in a trip and fall accident.  After the accident, several hidden turf depressions were “sanded” to fill  depressions to proper grade.

Not all landscape hazards are open and obvious.  Even a perfectly installed landscape may develop hazardous conditions if not regularly inspected and maintained.

Irrigation systems should be monitored, inspected, tested and adjusted monthly.  Turf should be trimmed around utility boxes and vaults regularly, aerated and de-thatched annually to maintain optimum performance and minimize grade changes.  Drainage structures should be grade adjusted, repaired or replaced when damaged.  Valve, electrical and junction boxes should be monitored for grade changes and adjusted as required.  Bark mulch thickness should be monitored and supplemented annually to maintain proper coverage and grade.

In summary, a properly installed landscape is composed of several systems and components that require regular ongoing maintenance for optimum performance, efficiency and safety.  Pro-active landscape maintenance may reduce potential hazards, resultant accidents and lawsuits.  These actions demonstrates an Owner’s recognition of protecting the health and safety of the public, pedestrians, friends and family who may visit and use the site and may prove useful in a legal action.

Arborist Online Learning Opportunities in the Covid Era

In a recent blog, I discussed using online media for a site online site inspection involving a Torrey pine tree root conflict with adjacent asphalt paving.  That marked the first time I used an online media tool rather than being physically present at the site.  My client and I used Facetime to conduct the real time inspection.

As the restrictions ease, I believe the use of online media such as Zoom, Hangouts, Facetime etc will increase.  I have already presented this concept to a legal client in Northern California concerning an irrigation inspection.  Do I really need to fly from San Diego to San Francisco, rent a car, drive to the site, observe irrigation defects, then reverse the process returning home or, can I watch the inspection over the web?  The level of scrutiny required depends on the individual case.

A slide from Dr. Smiley’s presentation

Like so many other industries, the tree industry is rapidly adapting to the new Covid – 19 reality.  Today, I attended an online Zoom seminar titled Sidewalks, Urban Plazas and Tree Roots.  This seminar was presented through the ISA Southern Extension.  I believe it was originally going to be part of a “normal” ISA Southern Association Annual meeting that was cancelled due to Covid.

The online presentation occurred through Zoom with over 1000 arborists throughout the U.S. and other countries attending. The topic concerned tree roots damaging sidewalks, presented by Dr. Thomas Smiley.  Once a few technical glitches were adjusted, the presentation was almost identical to what I had experienced attending many seminars.

The slides presented alongside the audio streaming from Dr. Smiley was easy to view.  I became immersed in the content and found myself taking pics of some of the slides.  The topic provided test data results using different techniques designed to reduce root intrusion beneath sidewalks.

Incorporating root growth inhibitor practices

 

The presentation lasted an hour, same amount of time I’m accustomed to when attending a seminar.  Although I already knew a great deal about the topic, I still came away with new information for use in my practice, including a great specification detail incorporating multiple root growth inhibitor practices that may reduce sidewalk damage due to roots.

In the past month, I’ve been able to continue my consulting practice from my home office.  I’ll continue to utilize more online media tools, whether for learning, conducting site inspection work, and client meetings.  I believe these new opportunities are one of the (few) beneficial results from the Covid-19 virus.

I recently provided a client with a proposal to develop landscape maintenance specifications for commercial properties located in several different climatic regions.  The proposal did not include any site visits.  All data collection would occur online through various means.  Using online data collection versus conducting multiple site visits saved the client thousands of dollars.

I’m looking forward to these new opportunities utilizing online media sources as potential replacement for physical presence.  Hopefully it will prove an efficient, effective, cost saving technique without sacrificing product accuracy.