Final answer:
A ground fire is a type of fire that burns below the forest floor in the humus layer of the soil. It can smolder underground and have significant ecological effects.
Step-by-step explanation:
The type of fire that burns below the forest floor in the humus layer of the soil is known as a ground fire. This type of fire is common in forests and can be challenging to fight because it can smolder underground and spread without being visible on the surface. Ground fires can have serious ecological effects, as they can damage the roots of trees and other vegetation, leading to long-term changes in the ecosystem.