Tree Managers : Public Discussion

Through my own experience of dealing with hazard trees over twenty years, it is my carefully considered opinion that QTRA is misleading in its use of the term 'Quanitified'; quantified risk assessment in other fields is based on complex statistical modelling. In comparison, the data we have on probability of failure is very poor. There are powerful factors that remain outside of predictability e.g. the weather and risk of hidden factors would also need quantifying.

In this respect, QTRA is a 'qualitative' assessment, based on broad objective criteria that can be applied to ascertain priority based on reasonable practicability.

The risk is that applying a statistical approach can lure the duty holder into a sense of security. If they percieve the risk to be low, routine tree managment can be neglected. This could offset risks to a later stage at a higher level with reduced options - neglected trees are difficult to safely retain and manage. The scurrent statistics of death may be nothing more than the result of twenty years routine tree maintenance to BS3998:1989.

The world financial crisis is a rude remider of how quantified risk assessment in the banking system failed to assess the net effect of various risks compounding one another to create serius consequences, and failure to act cautiously with such risks because they were perceived to be too remote.

There are parallels with tree risk assessment; just because we don't expect something to happen doesn't mean there isn't a 50% chance that it will. That point needs to be stressed to the duty holder for them to decide if they are prepared for the possible consequences. I feel the name and use of odds of QTRA system doesn't explain the brevity of this issue.

Use of statistics to draw odds, is a little like driving down the motorway looking in the rear view mirror. Climate change and the weather are big variable factors on tree risk assessment (always assuming a target), and that requires caution.

Regards
PDB