Answer:
No,it is not important that it must be only fire it may be other source also
It is true that Australia is self sufficient in supplying it's own people with food. Even though the land is semiarid and a desert, they still are one of the world's major exporter of wheat, dairy products, and meat among other things. They are also a major exporter of wool for the world. The country relies on live stock and crop farming for their food supply.
I can give you one:
One of the theories (in which i mostly believe in) is the one when every period of time, the climate changes. Now, we are in the warmth period, but after this period, there will be a cooler climate, and keeps repeating every while (think about the ice age)
Brunei's greatest export was petroleum.