Risk of Failure Experiment

[Buzzsurgeon]

I'm interested in the different assessments of risk that people have when looking at the same defect.

 

Take a look at the Oak below. Forget the targets - just ask yourself the following question...

 

Out of 100 trees like this, how many would you expect to see fail due to this defect within an average 12 month period?

 

There's no right answer and I'm not trying to catch anyone out - just interested in the results.

 

Cheers.

 

Average max age oak 300 years; age, pathogen or structural failure

Tree approx age 150 years

Average time remaining 150 years

Minus 50% due to severe stem decay

75 years left divide by 100 trees

0.75 trees lost per year average

 

Just a calculated guess?

[ArbjobsNick]

TOny this is a cheeky little experiment and not really fair Chatsworth have huge anchient oaks with very little crown hollow and rotten and very few have failed. Risk of failure has to be based on the wind sail area and location (protected / unprotected) decay advancement (Matteck) as a "Consultant" you have to protect your liability not just be a tree hugger. Who knows when that tree will fail ? and as you wont get 100 exactly the same you cannot work this out on a percentage scale. Each tree has to be assessed individually a timely and expensive project, good luck.

Nick

[samarb]

I suppose it's all relitive, as conditions per tree during the year may differ, good exercise though.

[Amelanchier]

TOny this is a cheeky little experiment and not really fair Chatsworth have huge anchient oaks with very little crown hollow and rotten and very few have failed. Risk of failure has to be based on the wind sail area and location (protected / unprotected) decay advancement (Matteck) as a "Consultant" you have to protect your liability not just be a tree hugger. Who knows when that tree will fail ? and as you wont get 100 exactly the same you cannot work this out on a percentage scale. Each tree has to be assessed individually a timely and expensive project, good luck.

Nick

 

Ah but Nick, I'm not really interested in the tree - it was an illustration. I'm interested in individual perceptions of likelihood of failure.

 

What I was hoping to find (and the second experiment did kind of get there) was a normal distibution of answers. And if you plot normal distributions you get a phenomena known as the bell curve which I was hoping to see in the poll graph. Now it didn't happen in this poll graph because I failed to break down the lower end of the scale but the second attempt was more successful.

 

Relevance? Well knowing the mid range (i.e., the centre 50%) of the data gives an statistical indication of a baseline for the perception of likelihood of failure. A baseline which might be used to level the arguement playing fields.

 

Another thing which would be nice to look at was if arboricultural knowledge affected the placement of this baseline and if so, to what degree...

 

So anyway - that was the reason behind the experiment not an actual assessment of the tree which is understandably what everyone went with.