In the lecture, the professor explains how fires benefit a forest.
First, the professor mentions fires promote the growth of new vegetation. They incinerate the canopy and underbrush. They make sun to penetrate, so new vegetation can grow quickly. Moreover, organic materials are burnt, releasing new nutrient to the soil.
Second, the professor mentions fires eliminate harmful parasites like fungi and insects. Infested forest is drier so it is susceptible to fire. Therefore, fire can completely destroy forest and remove insects.