Interesting points. I wonder, what does a raccoon weigh? at what point does that become a deciding factor? To what extent has decay broken down fibers where the tipping point is that animal landing on the tree. Maybe it's at what point does the moment force exceed the shear strength as it climbs further upward?
Material strength, wood amongst them is a science and one that is applied daily. We are calculating not just at what point will the material, (species) fail but over how long and under what conditions? Look at destructive testing of products, they are put through cycles of typical use to gain an understanding of what it takes to fail and over what period of time. There is always the caveat that there will be other factors and dynamics that will alter the results and thus the estimates give.
Maybe it's the cost in time (=money) that we feel we can't give clear answers. Is it beyond the scope of work most tree services offer yet, we are asked to give some sort of assessment. Even in saying we don't know there are factors we take into consideration that are part of our collected knowledge that gives us expert insight into tree's structural dynamics. Unlike the layman who says, "I dunno" out of ignorance, we say that but enumerate the reasons the answer can't be definitive.
If you had all the time and resources to come up with some sort of answer, what would you do to determine, to some degree of confidence, with the usual disclaimers and limitations, a range of time or maybe even conditions that will determine the outcome?
I would want to:
- determine the integrity of the root system and soil structure (think of that video of the forest floor "breathing"). To what degree has the decay diminished the root system. Has the increased water level adversely affected the soil?
- examine the fungi and the degree of decay at the root plate. Maybe a conversation with a mycologist to gain a better understanding of the impact on the wood by that particular species.
- identify the tree species and cross reference any information on its strength and typical decline under these conditions.
- learn what is the usual rate of decomposition in this area for this species? Are there any available studies that could infer such information?
- review weather conditions historically and forecasted. What over it's life has it been subjected to and consequently reacted to.
- ascertain when the observed defects occurred and to what degree have they reduced the tree's strength.
What else is there?
And I've still not ventured a guess at how long before it falls.
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