In the Trunk Formula method, as I read about it in Guide for Plant Appraisal, it appears that I can derive Unit Tree Cost from wholesale cost, retail cost or installed cost. The resulting valuations are WIDELY different, depending upon which of these I choose. How can I make a principled choice amongst them?

Or am I misunderstanding something?

Bill, I don't think you misunderstand anything. I have the same question. I called ISA and did not get an answer. I have been using the retail because it seems fair. When I used the installed price I had one black walnut tree, nothing special about it, come out to 60 some thousand. I did not feel that was realistic so I used the retail on that one too. It doesn't seem as though we should be using subjective criteria like that but I didn't know how to decide. Everything else seems straight forward except that area. If you want to talk about it - email me personally. dan@treedoctor.org Good luck. Dan