The Forest Biome has a dark green ground and is heavily populated by trees. It frequently has Spider Dens and Graveyard inside which can be hard to see through the thick foilage. Similarly, it is going to be denseles populated with Trees all over which can both be a danger and a benefit. The trees can make it quite difficult to safely start a fire but it makes it easy to collect plenty of Logs.
Since forests are so heavily wooded, not only is it easy to start a forest fire but it can sweep the entire area quite quickly. If you simply need to get through the area quickly to get to another Biome or location then this can be used to clear it of obstacles and enemies in one move. However, this will get rid of a huge swath of trees that you'll no longer be able to use.