Barkskin

When a priest casts the barkskin spell upon a creature, its skin becomes as tough as bark, increasing its base Armor Class to AC 6, plus 1 AC for every four levels of the priest: Armor Class 5 at 4th level, Armor Class 4 at 8th, and so on. This spell does not function in combination with normal armor or any magical protection. In addition, saving throw rolls vs. all attack forms except magic gain a +1 bonus. This spell can be placed on the caster or on any other creature he touches.

Barkskin Base AC

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Caster Level	Base AC
4	5
8	4
12	3
16	2
20	1
24	0
28	-1
32	-2

[Player's Handbook]

Sphere: Protection, Plant
(Alteration)
Level: 2

Range: Touch
Components: V, S, M
Duration: 4 rounds + 1 round/level
Casting Time: 5
Area of Effect: Creature touched
Saving Throw: None

Material Compnents:
the priest's holy symbol and a handful of bark from an oak (consumed)