This was never a problem until humans came along and decided to build expensive homes and commercial buildings in forested areas that eventually catch on fire. These "fire zones" would, of course, burn up sooner or later, but people wanted to live there, so they bought fire insurance and built their homes anyway.

The inevitable cycle of fire eventually arrived. Forests catch on fire from lightning or some other cause, but the only reason the fire spreads is because the forests are full of fuel in the form of fallen branches, shrubs and other combustible material. So the fires burn fiercely, as they have always done throughout the history of the planet, "cleaning out" the underbrush and giving many plants and trees a fresh start.