Some forms of fire and lightning will anger the animated forest, and some won't. There doesn't seem to be much logical distinction between the two categories.

Things that anger the forest: Fireball, Improved Fireball, Burning Hands, crystal of fire, Chaos Orb of Elemental Fire, Wand of lightning, Wand of ball lightning

Things that don't anger the forest: Fire Bolt, wand of fire, offensive alchemy, Lightning Bolt, Lightning Ball, elemental storm class power