Complex sentence: Because such fires happen annually, there is no great build up of dry fuel in the bush, and so the fires are not usually devastating, but may kill animals, and may damage crops if the rains end early and they happen before harvest.
Split into simpler sentences: Because such fires happen annually, there is no great build up of dry fuel in the bush, and so the fires are not usually devastating. They may kill animals, and damage crops if the rains end early and fires happen before harvest.