TreeLife Investigators: Vol. 1 – Tree Root Traffic Jam

There are many forms of investigation in the professional world. Everyone has seen movies with crime scene investigations or read stories derived from investigative journalism. Many people know firsthand about the investigation that occurs when a doctor evaluates a patient. More recently, there are the computer technicians who investigate computer problems. But most people don’t know about the investigation that occurs daily in the little-known world of arboriculture.

This story is about a TreeLife Investigator who was recently called out to a 'tree crime' scene. Most people would be surprised to learn that tree investigations occur regularly in many communities across the country.

This story begins with a population of bottle trees (Brachychiton populneus), planted in a homeowner association parkway ten years ago, that were showing varying degrees of health decline. The management company representing the community’s board of directors wanted to know what was wrong with the trees, and they contacted TreeLife to solve the problem.

An Investigator with TreeLife assessed the population of trees shortly thereafter and observed signs of secondary disorders in most of the trees. Many tree crowns appeared opaque, while others looked sparsely foliated. Leaf size was stunted on some specimens, and leaf tips were distorted and necrotic in others.

The Investigator noted that all of the bottle trees had three or four “breather tubes” (aka “root aeration tubes”) placed within one foot of each trunk. The tubes were arranged in a non-uniform, non-symmetric pattern. Often sold as beneficials, “breather tubes” were known to be ineffective and generally harmful. They don’t improve soil aeration or water distribution as advertised, instead they usually lead to root and trunk damage.

The TreeLife Investigator talked with a landscape maintenance account manager, familiar with the community, about the performance history of the trees. Purportedly their crowns would recover from the aforementioned secondary disorders each year only to decline or defoliate again.

The account manager remarked, “Like they will look good, then bad, then good, and so on. Like a never-ending cycle that is slowing getting worse.” Additionally, he told the Investigator that the soil was extremely compacted and difficult to work with. In his opinion, the “crappy” soil was the cause of the tree problems.

During this initial assessment the TreeLife Investigator observed an exudate coming out of the trunks of several trees. At first glance, he thought this might be signs of the Invasive Shot Hole Borer (ISHB), which attacks a wide variety of tree species by boring into their trunks. He removed pieces of the exudate to reveal the tissue below, but found no specific insect holes. The surrounding tissue was normal. If the tissue under the exudate had been necrotic, this would have been consistent with ISHB. Therefore, ISHB was ruled out as the cause.

The TreeLife Investigator continued with the inspection. He noticed that trunk flare, aka root flare, was apparent only on a small portion of trees. Additionally, dozens of trees had surfacing roots that wrapped around their trunks. Based on his eduction and experience circling roots that girdled trunks tended to restrict the normal flow of nutrients, and prevent the development of normal root growth.

Though not every ailing tree had obvious root defects, the TreeLife Investigator suspected that root problems were the most likely cause of the trunk exudate and other secondary disorders. He selected forty-four out of one hundred and fourteen bottle trees for an advanced assessment process known as root-collar excavation. More information was needed to determine what was really happening with the trees. And by removing the soil around their trunks he could better identify what the nature of the problems were.

Contrary to the landscaper’s opinion, the AirKnife cut right through the dirt like a butter knife would through butter. The soil was a sandy loam with some slight, clay-like striations near the surface. For the record, sandy loam was the ideal soil for tree roots and soil excavators alike.

Aside from discovering the soil was not difficult to work with, the Team uncovered what looked like multiple layers of topsoil. It seemed like the surface level had increased over time, and in multiple occurrences. This variance of soil types indicated multiple stress factors had been put upon the tree roots below — stress factors that were related to water absorption and root transpiration.

The Investigator knew that layers of varying soil types generally affects the movement of water. Soil science was complicated — but simply put, water may not move as expected when layering soil types. One layer may become hydrophobic in the presence of another soil type. When the movement of water is changed, roots may experience water deficit. Roots that stop receiving water generally will die under the right (or wrong) conditions.

And it appeared that the original soil level had changed multiple times around each tree. In support of this supposition, the Investigator and his Team exposed a multitude of root problems six to twelve inches below the surface.

They observed several “orders” of tree roots emanating from the trunk. That is, the size of roots coming out of the trunk varied in width. Some roots were millimeters-thin while other were inches-thick.

The Investigator surmised that each order of root growth emanating from the trunk was likely due to different disturbances. And the size of the roots corresponded to their age, which correlated with the amount of time they had been growing since each disturbance. Smaller roots were more recent, and larger roots were older.

There should be only one order of roots coming out of a tree’s trunk — the buttressing roots that provide mechanical support. These main roots may have branching roots, but the buttress roots themselves should be the only roots emanating from the trunk. There shouldn’t be fine roots coming out of a semi-mature trunk; fine roots on a big trunk indicate a stress factor. Therefore, the varying sizes of roots uncovered suggested several stress factors had been introduced.

The Team also uncovered subsurface irrigation hoses (which the Team later learned were inoperable). These inline drip hoses had been configured around each tree trunk. The drip hoses had been placed on top of the tree roots, then they buried under a few inches of soil.

While excavating another tree, the Team noticed a landscape employee removing lower branches on a section of parkway bottle trees. The TreeLife Investigator approached them, and asked why were they removing lower branches. They said it was for clearance — they had to push their mowers beneath the trees because the community was upset about tire marks on the sidewalks. They could not push the mowers on the sidewalks, and the branches were hitting their heads as they passed by each tree. They needed head space under each tree crown.

The reasons for all the tree problems became apparent to the Investigator, and a sequence of events came to his mind:

• The bottle trees were likely planted with root defects that developed in the nursery. Trees grown in containers often develop circling root systems if not corrected at the time of planting. The root defects were not corrected when the bottle trees were planted.
• The bottle trees were likely planted too deep. This made the trunk grow a new order of roots.
• "Breather tubes” were deflecting roots into a circular pattern.
• Though species was well-suited for dry environments, these bottle trees were planted in grass-covered parkways. Grass requires regular watering, which is essentially the opposite of the subject trees’ water requirements. The trees were getting watered too frequently.
• Soil had been added so the lawn mowers could roll easily past the trunks. This made the trunk grow a new order of roots.
• The trees were being pruned improperly. The injuries compounded the existing stress factors related to all the root problems.

They finished their advanced assessment and went home. The TreeLife Investigator concluded the assignment with a lengthy email to his client. It was not the happy ending he was hoping for. The advanced assessment uncovered several issues that could not be corrected.

It was a miracle the trees were still alive. The problems had begun to pile up when the trees were planted. Each successive year added a new problem. “Breather tubes” could not be removed without significantly injuring roots. Only a few of the circling roots could be pruned, and none of them could be truly corrected. The soil level under every crown could not be reduced; the community favored grass-covered parkways and clean concrete over tree-lined streets. The trees would likely continue to slowly decline.