SRD:Liveoak

This spell turns an oak tree into a protector or guardian. The spell can be cast on only a single tree at a time; while liveoak is in effect, you can’t cast it again on another tree. The tree on which the spell is cast must be within 10 feet of your dwelling place, within a place sacred to you, or within 300 feet of something that you wish to guard or protect.

Liveoak must be cast on a healthy, Huge oak. A triggering phrase of up to one word per caster level is placed on the targeted oak. The liveoak spell triggers the tree into animating as a treant.

If liveoak is dispelled, the tree takes root immediately, wherever it happens to be. If released by you, the tree tries to return to its original location before taking root.