https://blogs.scientificamerican.com/observations/fighting-wildfires-with-computer-models/

Many ecosystems in the United States developed in the presence of fire. Over millennia, flames have regularly swept across landscapes, often at smaller scales and with lower intensity than today’s forest fires. They cleared out excess fuels such as smaller trees, fallen wood and leaf litter in a self-regulating process that fragmented the landscape, limiting the size of fires and keeping the forest healthy. In many western forests, this resulted in widely spaced trees, thinner understory and less combustible litter on the ground than we commonly see now.

But human intervention has interrupted that natural process, allowing excess fuels to accumulate—and those fuels have got to go one way or another. For many years in the southeastern United States, land managers have engineered controllable, prescribed burns to remove a majority of the accumulated fuels on the ground; a significant amount in the forest midstory and some in the canopy.