Well, I was just shooting that blue print out there to see if anyone would give that a green light.
I'm sure of the forces applied there though. It's impossible for trees to fall anyway but to the big truck. The trick is being overly damn sure about the lines' tensil strengths all the way around and the size and power of the truck. A little Dahtsun Love truck might get sucked back into one of these kinds of deals and/or spin out botching the whole operation. A heavy chip truck would just pull it out even at their sizes.
I do agree that there is risk. It's a little like the "what ifs" in explosive demolition where teams are demoliting a building by imploding it with proper sequences of detonation each placed at key points. Ya, if it goes wrong, it can turn critical. When is this work not critical though. When it's done soundly, the quick take down proceedures save major money getting all of those stories of building to find it's way to the ground. "Man Made Marvels"
I have actually seen one of those jobs that was botched. The building just fell over, and actually rolled a half of a block to hit another apt. building. Wow. And you know that even a guy could slip with a part of the tree or a rope could slip or bust. It depends on proper gear, and proper placement.
What does the guy tie a zip line to? On one job I had a tree at the top of a steep gulley. Below the tree was a cactus garden. I planted a few screw in stakes down the hill, and zipped the stuff that way. The cable bowed to much for my likeing though. I'd have been satisfied with a tree down there to put a manual winch on.