I've embarked with 7 orcs and a large herd of animals to a temperate forest plateau with a volcano. I wanted to see how far animal-herding would take me, so I bought a lot of animals and pastured them among the trees.
The first year was uneventful. The second caravan comes, a caravan guard fights with something, but my orcs are inside, building the fort, so I'm not too worried. Then suddenly, the FPS drops. Uh-oh. I check the log. The guard was fighting some kind of magma-man. Then I check the surface.
The caravan guard was on fire. The caravan was on fire. The depot was on fire. Soon, the forest was on fire and so was my herd, which represented the better half of my embark points. My orcs could do nothing, as blaze consumed the surface. Of the herd, two boars survived. Of the eight-man caravan, we could only bury three. The rest were never found.
The orcs have switched to hunting.