#Go all Roman on them and salt the earth (sort of).

In the world I come from, there are no dragons, and so humans have instead turned their energies towards coming up with nasty ways to kill and torture each other. Some of these creative energies were channeled in what we now call the Third Punic War, where a place called Carthage was pretty much totally destroyed by the Romans. Stories tell that the ground was sowed with salt, essentially in an attempt to make it uninhabitable. Those stories are likely false, but then again, the Romans survived to tell them - not the Carthaginians.

Even if salting the earth actually happened, it probably wouldn't work very well, and at any rate, you probably don't have the massive amounts of salt needed to cover large areas of the planet. However, you're a large, flying beast with fire and apparently a lot of time on your hands. Your problem seems to be that you're not being sufficiently devastating when you destroy entire human settlements. They can come back and start anew.

Therefore, you can go about destroying the means of sustenance in an area, in some interesting ways.

• If humans like an area because it has plenty of wood to make buildings and spears and other things, burn down the forest.
• If animals are plentiful enough in an area so that humans can eat them, disrupt the ecosystem by scaring away the animals. Kill as many as you can, and frighten the living daylights out of the rest.
• If there's arable land for growing crops, burn the crops down when they try to plant any. Or encourage local animals to eat the crops.
• If there's a river nearby that's good for transportation, block the river (note: this works better for small rivers). Stones, trees, and other large objects can make travel inconvenient. You're strong enough to move these things.
• If there's a lake that provides fish and water, destroy any dams (natural or artificial) and try to drain the lake.
• Burn everything. To be honest, half of these suggestions boil down to that. Just light plants on fire. Humans don't want to get on the wrong side of a wildfire, and they probably don't have means of stopping it.

###Notes:

• These work on small scales, not continent-wide ones. Come on, you'll never rid the world of all the humans. But you can keep several small domains in check.
• Side effects may include the total destruction of all ecosystems in your area. Sorry.

Go all Roman on them and salt the earth (sort of).

In the world I come from, there are no dragons, and so humans have instead turned their energies towards coming up with nasty ways to kill and torture each other. Some of these creative energies were channeled in what we now call the Third Punic War, where a place called Carthage was pretty much totally destroyed by the Romans. Stories tell that the ground was sowed with salt, essentially in an attempt to make it uninhabitable. Those stories are likely false, but then again, the Romans survived to tell them - not the Carthaginians.

Even if salting the earth actually happened, it probably wouldn't work very well, and at any rate, you probably don't have the massive amounts of salt needed to cover large areas of the planet. However, you're a large, flying beast with fire and apparently a lot of time on your hands. Your problem seems to be that you're not being sufficiently devastating when you destroy entire human settlements. They can come back and start anew.

Therefore, you can go about destroying the means of sustenance in an area, in some interesting ways.

• If humans like an area because it has plenty of wood to make buildings and spears and other things, burn down the forest.
• If animals are plentiful enough in an area so that humans can eat them, disrupt the ecosystem by scaring away the animals. Kill as many as you can, and frighten the living daylights out of the rest.
• If there's arable land for growing crops, burn the crops down when they try to plant any. Or encourage local animals to eat the crops.
• If there's a river nearby that's good for transportation, block the river (note: this works better for small rivers). Stones, trees, and other large objects can make travel inconvenient. You're strong enough to move these things.
• If there's a lake that provides fish and water, destroy any dams (natural or artificial) and try to drain the lake.
• Burn everything. To be honest, half of these suggestions boil down to that. Just light plants on fire. Humans don't want to get on the wrong side of a wildfire, and they probably don't have means of stopping it.

Notes:

• These work on small scales, not continent-wide ones. Come on, you'll never rid the world of all the humans. But you can keep several small domains in check.
• Side effects may include the total destruction of all ecosystems in your area. Sorry.