Is This a Hazardous Tree

Basic Tree Risk Assessment

Here is a Douglas Fir or Pseudostuga menziesii leaning towards a child's play set and a family home.

Every Tree Is Hazardous

Every tree has the potential to cause harm. It's true, in fact just the other day I was walking down the street minding my own business when bam!@#$!. The side of my head glanced off the stem of a Magnolia stellata. I walked into it knocking my head. Stupid hazardous pretty little tree.

Every tree has the potential to cause harm to a degree. To avoid all chance of harm  we would need to remove all trees. I don't hear anybody supporting that idea. This is where the ISA, Certified Tree Risk Assessor comes in. Every tree is hazardous, but exactly how hazardous is it? 

Tree Risk Assessment Basics

3 basic questions to consider when determining if a tree is hazardous. 

1. Target    What will be smashed if a failure occurs?

2. Size of Part    How big is it?

3. Probability   How likely is this failure?

Consider the leaning Douglas Fir...

1. Target: The tree is leaning over a child's backyard play swing set. If it falls we can be pretty sure about the location it will smash. The swing set would be obliterated and the Doug's top will strike the family's house

2. Size: Big enough. Based on the lean lets consider the possibility of full tree failure. This guy is about 65 cm diameter at breast height, and pretty tall. Full marks for size.

 That takes care of points 1 and 2. Now comes the tricky part.

3. Probability: Keep in mind that determining probability of failure must be based on fact. Though the picture doesn't show it there had not been any recent digging near the roots, nor was there sign of root heaving. We can see the lean. We can see the dead stunted branch pointing upwards. No other defects are visible. Looking up the stem the lean actually self corrects, the tree straightens up.

Should We Cut Leaning Doug Down?

Put yourself in the shoes of the arborist whose job is to determine whether this tree remains or is destroyed. What would you do?