Tree Managers : Public Discussion

Whilst the system produces statistical data, I have yet to see research data to support its accuracy. Based on Australian figures, the risk of death or serious injury is extreemely low (less than 1 in a 1,000,000 of population). Given that there are more than 10 trees for every person the odds of a tree causing problems is less than 1 in 10,000,000. How then do we account for the problems we do have? Clearly these are the result of trees that have a lot higher risk of failure that are high trafic areas!

Given that it is these trees that are the subject of risk it would seem that the data on these would need to be extreemely accurate. The concern I have is that the assesment is subjective and not quantataive at this point. Yes the tree does have girdling roots but can I say to what extent that this has impacted on the stability of the tree and the thigmomorphogenic responses. As a result we generally err on the side of caution and assume the risk is higher than it is. (Hence the Wessolley Mattheck debate)

Clearly any program that considers the size of the falling parts, the probable frequency and the target must pick out the more hazardous trees (eg the ISA hazard assesment program) but how is this subjectivity converted into statistical accuracy without reseach data?

If any arborist can tell me the liklihood of a 100mm dead branch falling I would like to know how they do so. Instead we assume that it can fall at any time and it will most certainly fail so we might as well be smart and remove or at least reduce it if we want to keep the habitat. On the other hand what are the actual statistical figures on death or serious injury due to the failure of a dead branch of this size. Again here in Austarlia the odds are very very small.

If 1 in 10,000 is an acceptable risk is there data for 10,000 trees at that risk level to prove or falcify the statistical assertion. Throwing the average tree with a risk factor of less than 1 in 10,000,000 into the data soop is surely poor ststistics.

In short what is the error factor and does the data consider the mean, mode, maximum, minimum or average liklihood of any event. What is the statistical difference between the minimum and maximum (the error factor) and how have these figures been proved? I certainly would hate to find myself in a court case because I acted too quickly or because I did not act quickly enough.

Mark