In reply to Scorpio:
What you are describing are fairly standard rope access tasks. When it comes to rope access, normal climbing gear and climbing techniques are generally entirely inappropriate.
For the 'work' tasks you describe, doing anything other using industrial rather than purely recreational equipment and adopting the standard industry practice of using two entirely independent safety ropes is pretty foolhardy. The basics are not rocket science but equally there is vast scope for novices to make a whole variety of errors.
I think anyone giving you any advice other than to get some specialist training or book yourself on an IRATA level 1 training course (see
http://www.irata.org/ ) would be doing you a dis-service.
That said, browsing through the Petzl Professional Catalogue (45MB!) will probably give you a fairly decent idea of the methods and equipment used in industry -
http://www.petzl.com/en/pro/catalogue/login
When it comes to tree surgery, that's a rather different set of skills and techniques yet again. Even as someone who does roped access tasks professionally, I'd prefer to hire a professional tree surgeon rather than mess around up a tree with a chainsaw myself.
PS Working for one employer, we occasionally rig zip-wires and high-ropes courses from mature trees but we will always use long ladders wherever possible. Rope access techniques are always the last resort, not the default.
Post edited at 21:42