I watched the webinar on risk assessment by Dr. Andrew Koeser on Thursday. It was interesting to see his investigation, which was aimed at a worthy goal; finding ways to get more consistency in this practice. 3 points stood out:
Trees fail when load exceeds support. Load is half of the cause of tree failure. But the study showed that only 5% of 'advanced arborists' say that Size aka Load is a major factor to consider. This is not surprising, considering all the attention given to interior decay and "defects". But these conditions are difficult to treat, while one day's pruning treatment can last five or ten years.
Interior decay is important to investigate, with equal time given to tree growth and CODIT. Hollow and damaged trees tested at Biomechanics Week stood stronger than undamaged trees. Load gets excessive and risk gets high when trees and branches get overextended. But Koeser's data showed that overextension or "size" is not considered important by 19 of every 20 assessors, professionals and amateurs. What does that tell us?
"False precision" plagues the process. Ed Gilman pointed out that "We know next to nothing about tree biomechanics". Still it is easy to get carried away, and claim impossible knowledge.
Mitigation and residual risk are not conclusions that follow the assessment process. Looking at A300, the BMP, and the form, mitigation seems more like the result--or an afterthought. But rating residual risk (often Very Low), after specified management, provides vital information. And the expense would not be great for any reasonable treatments.
Reconsideration based on specified work (whether or not it is done) provides a realistic perspective, and a balanced view.
Andrew's work gives us good food for thought. Maybe his next study could address the potential for consistency if balanced attention was given to the (often Very Low) residual risk after mitigation.
