Yeah that's a lot of lichen. It shouldn't concern you beyond the fact it could make things more slippery. The lichen aren't "feeding" on the tree, only using it as a surface to grow on and sponge rainwater from. The extensive covering suggests this tree is in an advantageous micro climate for...
Here is an example: http://www.ebay.com/itm/Take-Five-025-Winter-Warm-Compression-pants-Skinny-pants-Sportswear-Base-layer-/121452362972?pt=US_Mens_Athleticwear&var=&hash=item1c471ffcdc
For me and winter work (Minnesota) its gotta be a moisture-wicking base layer. I buy a brand of long johns (bottom and tops) called Take Five off Ebay. They come straight from the manufacturer in Korea, so you will have to wait 10 days or so for them to arrive. But they are gold, and only cost...
Arborplex was my first climbing line, the price was right. This was with a Weaver buttstrap saddle and tautline hitch; pure ass-busting. Get some XTC or something, it will be worth your while to pay a little more and skip the Arborplex. Like others a have already stated, its a good light...