In this article, we delve into the importance of tree risk assessments, explaining how they help prevent potential hazards and assist with safety in your community or property. Learn about the latest techniques and best management practices used by arborists to evaluate tree health and stability effectively.
Tree risk assessment used to be called hazard tree assessment. A great book was published by that name back in 1993. Just by changing the wording to risk assessment, arborists were able to focus differently.
Trees are living things. Their structure and form above ground is what we are used to seeing. That goes for measuring and appreciating trees as well. But the below ground portion, the root system, has about as much woody mass as the parts above, and it is essential to understand roots and soil.
Think of soil as a skeleton. When it is dry it holds together great, but when rain or meltwater infiltrate, suddenly, all the solids are lubricated. Little spaces of air and gasses below ground, called pore spaces, fill.
If you have ever seen a tree that fell over, there are two types of roots you may observe. The first is rotted. That means the root structure is small and contains mostly wood. The second is a healthy root system. Healthy roots originate like spokes on a wheel and get smaller as they get farther from the tree. In fact, tiny hairlike roots do most of the uptake of water and other nutrients that trees absorb. The thicker roots are for storage of nutrients (from the crown and the roots) and for holding the tree upright. But in a way all of the root parts do all of the jobs, storage, uptake, and under structure.
The trouble with assessing roots is that they are underground. You can dig them up, use water or air to expose some of the system, but remember, there are many and they make up as much of the tree’s weight as what we see above ground.
In figuring out how well a root system is doing, arborists look for signs and symptoms of root decay or root loss. Sometimes, a trench is dug too near a tree and the tree heaves (falls over or partly over) due to the loss of roots. There are also factors such as the prevailing wind direction and wind speeds. Think of roots like the ropes of a tent. They are holding the tent in the wind only when they are on the windward side.
Above ground portions of the tree, such as stems and branches, can also cause damage if they fall. These are observed and noted. We use a form when we are qualified to do risk assessment. The most popular now in the US is the TRAQ, Tree Risk Assessment Qualification.
The basics of this way of quantifying a tree’s risk are: Can a part fail? Yes, we can answer. There is no safe tree because each will eventually fall. So we have to go deeper: Is it likely to fail? What part? And then; is it likely to strike something if it fails? And last, how is the space near and below the tree or tree part being used? If it is a doorway of a building it rates higher for risk than if it is in an overflow parking lot.
All these risks can be mitigated in some way. A branch can often be removed or cabled to a stronger part. A tree can be shortened so that it is a wildlife habitat tree, rather than a focal point of leaves, flowers and bark. And in many cases the ‘target’ can be moved. Doorways and crosswalks can be relocated in some cases. Trees can be fenced off from recreation areas.
This is a broad view of what tree assessment is and how it may fit into your plans for making your property more useful, beautiful and safe.