Firebreak

The firebreak spell renders all living vegetation in the area, including plant like monsters and animated plant life, immune to normal fire, and cuts all damage to such plants from magical fire in half Dead plant matter in the area of effect can still burn, as can living plants moved outside the area. The spell does not function indoors or underground. The caster can cover an area of 800 square feet per level (for example, a 10-foot wide firebreak, 80 feet long per level).

The material component is a bit of charred wood.