Wood stockpiles catch on fire nicely. So do finished good stockpiles that only accept wood, since you can turn 1 log into 3 tiles of fodder by not allowing bins in that pile. Lignite is always a good choice, but you may be using that for other things since it's become relatively rare. I would highly suggest ordering a lot of wood crafts from your manager, and making a large stockpile that takes no bins and only takes wooden finished goods (perhaps clothing too, if you want to get rid of that as well). If needed, have it Take From your main finished goods pile, to ensure that it's always full.
Also, artifacts will burn forever, so if you're feeling sneaky you can set up a trench in front of your entrance, which accepts only wooden and lignite artifacts (let's face it, you've got a ton of stonecrafting moods already). Cover this 1-2 wide trench with hatches, and then surround these hatches with pressure plates, linked to the hatches. The effect of this, is that when an enemy comes near, they'll flip the plates, forcing them to run into the trench. Because they move fairly quickly, they'll probably be able to leave the trench before the hatch closes, but by stepping onto the flaming artifacts, they will catch fire themselves. Or, if you want a more manual route, you could just link the plates to a lever, to expose them to fire when you get the siege warning.
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^This would allow a trench undernearth that would force anyone approaching to travel into, and possibly get trapped in, the trench. For additional security, you can have the trench expanded underground, allowing the invaders to path back towards the right. That way, in case they get stuck and the hatch closes over them, they'll naturally move away from the fire and towards the opening further away. So when your dwarves go to claim their copper and iron weapons, they won't jump into the fire to do so.
Granted, this isn't much about dragons, but you'll be dealing with a lot of fire and this could help.