I was certified years ago by a company. Don't know how else to do it.
Books give you an idea but you really need experienced trainers and practice. In my long career I have seen countless "certified" arborists and such. Those certificates mean little to me. I was a company evaluator for a co. in California. I evaluated all new employees and set their wage and position. Some of these guys would hand me their "papers" and I wouldn't even look at them. I could watch you for an hour and know if you were good or not. Once I was told to evaluate a guy for a foreman job. I took him out with me for the day. At the end of the day I called my boss and recommended the guy be placed no higher than an apprentice climber. The CEO of the company overruled me and gave this guy a crew. A week later he cut himself out of a tree and was killed. It seems he reached around the back of the tree to cut a branch hanging up his flip line and accidentally cut his rope (you can't use steel core ropes on power line jobs). He had all the certificates. Now he has one more, a death certificate.
Rescue from trees is relatively simple. Always lower a guy on his own rope if at all possible. Take an extra rope with you in case you need it. Know how to tie a false crotch. And always carry a knife. Beyond that it's no different than roping out an overhang.
