Here's a few of my thoughts:
1. Canopy reduction, versus canopy thinning. Both will achieve the desired outcome, which is less weight on the limbs, consequently less forces acting at the point of attachment. Canopy reduction reduces the leverage effect, whilst canopy thinning simply reduces that weight along the limbs, and throughout the tree.
I think a balanced, well-executed thinning would have been better for this tree. However, I think both will be pretty close in end result, in terms of force reduction at the point of attachment. I would say it depends more on what the home-owner wants aesthetically in this situation, open canopy (more light, natural tree structure) versus smaller tree.
2. I'm amazed people still bolt trees and drill holes through them to "help" them. I'm a firm believer in non-invasive cabling and bracing strategies.
With that being said: I don't understand why the arborist used both steel cable and textile cabling ... honestly no idea.
Second, you are right in that he did not install his Cobra lines correctly. There should be additional bracing higher up in the canopy. See image below for 2/3 of the tree's height.
3. I'm glad to see that the homeowner wanted to protect / prolong their tree's life. Where I live, if I had submitted 1x $2400 bid to cable, brace and prune it, and 1x $1800 bid to cut it down, you can bet they'd be asking if I can grind the stump too.
Interesting situation to discuss.
What I think can be very helpful in winning these types of bids, is putting down in writing on the written estimate, that you will be adhering to ANSI 300 Supplemental Support Systems specs. (American National Standards Institute). Are you an ISA Certified Arborist? (Just curious why they chose your competitor instead of you)
Also, make sure to include that inspection is necessary every 3-5 years, or however you want to market it. Call the customer back a week later and ask them if they have any questions.
Explain everything you will be doing. Tell them why it will cost them $2400, and why they should pay you (you specifically) to do that.
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