Tree crews can barely open a magazine or attend a trade show/conference without seeing articles, advertisements and/or presentations on hazard trees, risk assessment and tree dynamics, yet there often seems to be some confusion among field personnel about what those topics encompass.

Certainly an important part of a tree care industry professional’s job description is being able to tell a homeowner, landlord or public/private organization which one of their trees might be a “hazard” and why, but equally, and perhaps even more important, is that each and every member of those tree crews, all “field personnel,” recognize what might make a tree a hazard to work on. After all, a tree can certainly be a hazard just “sitting there,” looming over the house or sidewalk, but add in the forces and fun of climbing, rigging and cutting loose large, woody debris, and the hazard potential goes way up, even on a tree that was deemed no threat to life or property.

There are certainly differences between a hazard tree assessment and a tree work assessment, but many elements are the same. The primary difference is what the crew needs to do to the tree to accomplish the task at hand. An introduction to the principles of tree dynamics and risk assessment can go a long way toward helping crews identify trees that require more “care,” keeping themselves, and their pieces/parts, as safe as possible.

A pretty obvious example of a previous lightning strike on the trunk of a tree. Photo: Matt Logan

A pretty obvious example of a previous lightning strike on the trunk of a tree. Photo: Matt Logan

The dynamics of a tree

Tree dynamics is simply a term used to describe how a tree moves. The movement might be in response to everyday factors such as wind, or more tree care-specific forces such as rigging or the removal of a large limb. The natural dynamics of the tree could be the development of different types of wood in particular parts of the trunk in response to prevailing winds, or buttressing roots as a means of support in certain growth situations. These, and many more, are all examples of how the tree as an organism has adapted to its particular environment for survival and stability.

A tree, even in a slight breeze, is hardly a motionless object, rather it uses its entire structure to absorb and dissipate the energy to the wind. In much the same way a tree will use all of its structure to absorb the energy when a climber removes the top or a branch. This movement is generally a positive sign, meaning the tree is functioning as a unit to dissipate the energy. A branch or lead that shows a lack of movement during moments of force may be a red alert that something is keeping that force from being transmitted, perhaps a pocket of decay or some other type of break in structural integrity.

The tree’s “energy absorption” system should definitely be checked out prior to starting work, as it can show problems and may even illustrate how the work will need to be carried out.

Look before you leap

The first, cheapest and often best assessment of the tree is one in which a tree care professional is looking at it, and this needs to start with the salesperson, bidder or company owner. No tree crew should show up to do the job and be the first tree care folks to have “eyes on the target.” That first assessment will make sure the crew has valuable information about what kind of gear and equipment is required, and, even more importantly, what kind of obstacles and hazards they need to be aware of and watch out for.

Even given a thorough prework assessment by a qualified evaluator, the crew needs to do their own on site prior to starting work. Human error is a part of life, but if something was missed the time to discover it is not when the top is falling into the rigging. In addition, depending on the time span between bid and work, any number of factors could have changed that affect the tree’s stability and safety, so a prework hazard/risk assessment should be a part of every tree crew’s routine.

Visually inspecting the tree means going all the way around it, both near and far, beyond the drip line and close to the trunk, as too much can be missed otherwise. All crew members should be a part of this inspection, as they all need to be aware of the hazards the tree might present.

Red flags

These are warning signals that the crew needs to be alert for. They don’t mean the job can’t be done, but they do mean that the crew better look closer at what the red flag is waving from prior to starting up those saws. While the following is a short list of red flag indicators, there are many more that might appear, and crews carrying out risk assessments need to be observant and alert to their presence.

  • Cracks — either horizontal or vertical in any part or parts of the tree’s supporting structure
  • Fruiting bodies — any sign of mushrooms or other fungal fruit aloft or in the rootzone of the tree
  • Codominance — signs of double or multiple leads or branches at the same point of origin with included bark
  • Lightning — any visual evidence of, or homeowner’s testimony of, lightning striking the tree recently or in the distant past
  • Bugs — signs and symptoms of insect presence, both those that are harmful to the tree’s structural integrity or to the crew’s health (bees and wasps)
  • Holes — signs of decay and empty spots in the trunk or tree’s major structural parts (this can include signs of cavity nesting birds and critters)
  • Digging — any signs or verbal reports of recent construction or disturbance (compaction, grade changes, trenching) in the rootzone

Pull testing

This simple process not only shows how well or poorly the tree might deal with climbing and rigging, but it will also show the tree’s “personal” dynamics. The pulling should be done with a throw line rather than a rope, as the goal isn’t to break anything, just to get some movement going in the canopy.

Placing the throw line fairly high in the tree will give the best results and testing. It should be pulled both downwards and sideways to try to mimic the forces that the tree is going to experience during the work process. While the “puller” should certainly be looking at various areas of the tree for cracks opening or areas of no movement, so should the rest of the crew, as the goal is to try to get a picture of the tree’s dynamics from all angles. The rootzone should also be observed during pull testing to watch for any heaving or cracking that might be going on in this vitally important support area.

Quite vivid fruiting bodies in the static relevant zone of a tree. Photo: Michael Tain

Quite vivid fruiting bodies in the static relevant zone of a tree. Photo: Michael Tain

Roots and static relevant zone

Any fruiting bodies on the tree or roots should have been discovered as red flags during the visual inspection, but an area to also check closely both prior to and during pull testing is the static relevant zone. This part of the rootzone has been proven to be very important to tree stability, and is about equal to 150 percent of the tree’s diameter. It extends out from and around the root flare, and may be irregularly shaped depending on the footprint of the tree.

Dividing the tree for evaluation

The accompanying form, developed by Dwayne Neustaeter of Arboriculture Canada Training and Education, is called the Integrated Risk Assessment Guide. It is used by a number of companies and organizations in North America to evaluate trees for risk in general and prior to work. The division of the tree into different sections for assessment may be unfamiliar, so a description of each section follows.

  • The scaffolds are those leaders and branches that make up the structure of the tree’s canopy.
  • The trunk is the continuation of the trunk of the tree beyond its first branches.
  • The pedestal is the lowest portion of the tree’s trunk from the rootzone extending up to its first branches.
  • The roots are the rootzone along with the static relevant zone.

Each section of the tree is checked out visually, and additional evaluation done as needed for red flags and the like. In addition, the form includes sections such as the particular risks of the site; what type of work will be done on the tree; and more in-depth evaluations such as sounding, drilling and pull testing.

This form can be integrated as is into individual companies existing prework process, or parts of it can be added to an existing form; the important thing is that some form of prework risk assessment be done. Additional practice and training in the use of the form is helpful, and users should make sure that they fully understand all the factors that are being scored and evaluated prior to betting their life on it.

While this is only a brief introduction to tree risk assessment, it should give tree crews a better idea of how to look at the tree prior to starting work on it, and with time, training and practice lead to safer and more efficient tree care. If nothing else is taken away from this discussion, readers should at least realize that to not look closely at the tree and its dynamics prior to working on it is a good way to end up wondering what went wrong.