It's very normal, although fires can start anywhere, often even spontaneously given enough heat and dry static. Trees that have been lightning struck more often than not are struck somewhere between midway up the trunk and the crown and the crown will catch very quickly. No matter where a fire starts, the fire and heat rises so the crown is always going to get hotter and catch fire faster than at any other level on the tree. You know what else is normal - at least here in my province - 10,000 lightning strikes a day in or near places that are already burning because the heat from fires causes it's own weather and creates lightning. Just like the lightning you see directly above actively erupting volcanoes, the heat causes the lightning.Do fires normally start in the crowns of trees?