ELi5 How does forest or grassland catch fire, does it always need a spark or can drying out cause spontaneous combustion?

Question

ELi5 How does forest or grassland catch fire, does it always need a spark or can drying out cause spontaneous combustion?

In: 3

Answer 1

Just to add to the others. A peice of broken glass left from years or evan decades earlier can catch the sun just right to cause an ember. Enough to ignite dry grass underneath