Fire can have some exciting effects on the fertility of forests and ecosystems. Usually, fire results in the deposition of ash into the soil without the soil being burned too much. If a forest has unusually dense and dry humus, this will be burned, too; this can profoundly affect the soil's microbiome.
Deposition of ash chemically changes the soil; if there are pH changes, this can change the amounts of ions available in the soil as organic residues present in the soil will release nutrients during a pH change. This interaction has been known since maybe even before humans fully understood agriculture. Using this method for forest management has consistently resulted in fertile forests for years. This fire can also be seen as a primary function of the nutrient cycle and should not be ignored if we scientifically understand the basis of this fertilization function.