The skill presupposes the tree will be able to support the weight of the climber. The answer to the puzzle, how much can a tree limb support, is complicated and can be simplified by allowing any climber to support themselves on any trunk thicker than 2 inches, and any branch thicker than 1 inch. Branches of such a size will naturally run out at some point above the ground. It is suggested that the amount of tree that can be climbed, dependent on species and age, be judged case by case by the DM.
Unskilled Tree ClimbingIn some degree, anyone can climb a tree ~ but unskilled persons tend to climb more slowly, with a greater hazard, as they lack the knowledge of how much a tree limb can bear.
The first obstacle is getting into the tree, the first eight to ten feet of which, depending on the species, may lack branches. An unskilled climber will require 5 action points (AP) per 2 feet of climbing. Some will employ a ladder or the help of a push in order to move above the trunk, to where branches can be used. Once the branches are reached, the speed of climbing can be increased to 1 AP per 1 foot of climbing.
For every 20 feet of climbing through limbs, characters must make an ability check, based upon their intelligence, wisdom or dexterity, whichever is highest. This reflects the character's inability to choose a good footing as they climb. Any missed check is considered a fumble; the individual will fall partway through the tree, suffering 1d4 damage. At this point, a dexterity check must be made; if this fails, the character will fall all the way to the ground, taking damage along the way (see Falling). Falling out of a tree is very dangerous.
As always, rope can be used to support a climb. An unskilled climber, using rope, can increase their pace 25% when climbing a tree.
Skilled Tree ClimbingA skilled tree-climber, when climbing only a trunk, will be able to rise at a rate of 1 1/2 AP per 1 foot of climbing. When moving through tree branches, their speed will naturally be 1 AP per 2 feet of climbing; they will not find rope useful in aiding their climb. Skilled tree climbers will never need to make ability checks, unless fighting in combat (see Fight while Unsteady)