The elves have displeased me.
For many years I had a very agreeable trade situation worked out with the elves. Their caravan would show up every spring laden with precious wood. I would relieve them of the wood, and let them leave with their lives and perhaps a mug or two for their trouble. I had wood for bins and barrels and potash, and they had enough profit to come back the next year. Then something changed. It was about the time that uppity elven diplomat showed up to demand limits on our wood-cutting. Pageslipped is in a treeless desert, so the demand struck me as harmless enough.
Obviously agreeing to their demand was a mistake, for soon afterwards the elves stopped bringing wood and began showing up laden with other goods. Cloth, plants, exotic animals, seeds, and useless wooden weapons and large clothing. The first year I bought some of their new goods, purchasing a breeding pair of grizzly bears. The next year they returned again with more useless goods. Realizing that a steady supply of wood was worth more than another exotic animal or a few berries, I refused to deal with them, hoping they'd get the message.
They left without trading, then the next year returned with the same crap. Obviously the message didn't get through.
This winter I had my dwarves tear down the standard trading depot, and build a new one just for the elves. A wooden trading depot, surrounded by iron walls and doors, and connected by pumps to the magma lake. I do not intend to take their worthless goods. That would imply I placed any worth in them. I will burn elves, pack animals, cloth, useless clothing and weapons, plants, seeds, caged exotic animals, and the trade depot all at once. And I will continue this every year until they start bringing wood again.