Treeguy,
One of my uncles was a professional Arborist. When I was 14, I worked with him for a couple of weeks taking down a tree. Even though my job was to haul the limbs and debris away, I did learn to respect the difficult job the Arborist faces each day. The forces generated from catching a falling limb really impressed me. I really don't know much about the systems used for tree work, so it will take me some time to understand the issues and make meaningful comments.
You are welcome to use/post/cut and past/reference all or part of my article as you wish. A copy of the powerpoint presentation that was presented at the International Technical Rescue Symposium (ITRS 99), Fort Collins, Colorado, 1999 can be found at
http://www.attawaygems.com/ITRS2006/Friction_talk.ppt. The paper can be found at
http://www.attawaygems.com/ITRS2006/Friction_ITRS99.pdf. You may use the images in the powerpoint as needed.
A follow up to the friction theory paper was a paper by Tim Manning which tested the theory for rope friction on rock. Tim's report can be found at:
http://www.mra.org/services/grants/ManningPaper.pdf
Some of our latest efforts to understand rope behavior in dynamic falls can be found at
Strike Rescue: Research
Stephen Attaway