What the hell is a treetrunker?

I joined this forum in the last 2 weeks and all I hear is endless talk about treetrunking and treetrunks? What the hell are you guys on about. Is it an american slang word? Or is it a word used in astrology since its all over the astrology discussions but nowhere else............

I've been trying to figure that one out too..

So what the ---- is a Treetrunkerf——??