Transmutation
Level: Druid 2, Incarnate 2, Mystic Ranger 2, Ranger 2, Plant 2, Urban Druid 2
Components: V, S, DF
Casting Time: 1 standard action
Range: Touch
Target: Living creature touched
Duration: 10 minutes/level
Saving Throw: None
Spell Resistance: Yes (harmless)
Barkskin toughens a creature’s skin. The effect grants a +2 enhancement bonus to the creature’s existing natural armour bonus. This enhancement bonus increases by 1 for every three caster levels above 3rd, to a maximum of +5 at caster level 12th.
The enhancement bonus provided by barkskin stacks with the target’s natural armour bonus, but not with other enhancement bonuses to natural armour. A creature without natural armour has an effective natural armour bonus of +0, much as a character wearing only normal clothing has an armour bonus of +0.
Source: Player’s Handbook (Page 203)