Double Rope Technique (DRT)
This is the safest method of roped tree climbing, and utilizes a dynamic climbing rope draped over a large branch so both rope ends descend from the branch together toward the ground. A friction wrap, such as the Blake's hitch, or a prusik, is used as a belay while climbing so the tree climber's harness is held securely to the rope while ascending the tree. A saddle is used to tie between the two rope ends with a set of prusiks which allow the saddle to slide in either direction. However, if weight is suddenly put on the saddle, the saddle's prusiks constrict around the climbing rope, preventing you from falling.
Single Rope Technique (SRT)
Single rope technique utilizes one end of the climbing rope tied to the base of the tree or a branch as an anchor, and uses mechanical ascenders that allow the climber to move up the rope; however, the ascender locks off when weight pulls it in a downward direction, preventing the climber from descending. When lowering from a tree using the single rope technique, it is best to use a belay device with auto-locking capabilities so you can control your descent. Alternatively, if you do not have an auto-locking belay device that can be used for rappelling, you can use a belay device with a friction hitch as a backup in case you let go of the rope while descending.
Safety Considerations
Select a tree to climb that does not have any signs of rot or mold growth, which may weaken the trunk and branches. Only attempt to climb a tree that has live branches and only attach ropes to branches that have buds and new growth. Always inspect your climbing gear and ropes for fraying prior to use. Also inspect the tree's roots and trunk for signs of decay or instability. As a safety precaution, the tree's trunk should be at least 18 inches in girth before attempting to climb it.
Equipment
In addition to using climbing ropes, belay devices and mechanical ascenders, you may also want to use a personal anchor system while you stand on a tree's branches and affix more ropes. A personal anchor system may consist of a cordelette doubled over and passed through the contact points on your harness and tied into a figure-8 knot. Other gear choices may include etriers, pulleys, and other pieces of technical aid climbing gear. Professional arborists may also use specialized climbing boots equipped with spurs to help climb trees more quickly.