I really like your thoughtful last sentence.
I am surprised no one called the tree out on a less than optimum cut at the point of infection (which appears to be saprophitic ?). About 10 years ago I was called to this residence with this (at the cut) giant limb laying on the roof. There was a good 6 to 8 inches of melting snow on the roof and the roof was broke wide open. The tree trunk was encased in ice...completely. I brought in my crane sub with a 50 tonner and I rode the ball, he injected me into the top of the canopy and I tied in, rappelled onto the roof, choked the leader, went back up and cut off the leader and boomed it off the house so the water flooding into the house could be dealt with.
Hadn't heard from this person for 10 years and then a second time about the maple after a call about the oak re pruning and cabling. I also entered a lattice work door under the deck and tree to check the buttress on the maple and found what appeared to be degraded Ganoderma lucidum between the buttresses. Varnished mahogany appearance and still identifiable. This tree is fully budded for next year.
My analogy to human cancer and alarming people extends to the point that if people are diagnosed with cancer do they end their lives immediately. Can dying/infected trees be made lower risk with pruning treatments and wring the most years possible from them until the time comes and the HO is ready for the loss? It is all very perplexing.
If I am called re a tree in obvious decline from whatever reason I often consider the feelings of the homeowner and try to deadwood the tree, make it as safe as possible...and continue to reduce and prune it as the deadwood dictates ...if I feel the risk level is low....until it isn't.
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