Much of California experienced a severe and likely unprecedented drought 2012-2015. The drought, in combination with forests that were vastly more dense than historical or ecological norms (due primarily to a policy of fire suppression for roughly one hundred years), incited widespread tree mortality. While tree mortality occurred statewide, it was centered upon the central and southern Sierra Nevada, and mostly occurred from 2014 to 2016, although elevated mortality is still occurring in some species today. Much of the mortality was executed by bark beetle species whose populations had in many cases reached epidemic levels. This was in large part due to trees that were too stressed—both due to drought and increased competition from overly dense forest stands lacking the natural thinning of fire—to be able to defend themselves from beetle attacks as normal with sufficient pitch. Ponderosa pine and sugar pine were hit especially hard, losing 80-90% of their population in many areas.

In the aftermath, vast expanses of primarily dead forests remain. Trees in their forests are also falling to the forest floor quickly, creating unprecedented levels of forest fire fuels in many areas. Neither mechanical thinning [i.e. logging, masticating (clearing) underbrush/small trees] nor prescribed fire are new concepts in western forests. However, as a result of the tree mortality and devastating fires in California, there has been an increase in the social license to execute these management techniques. There is now also significant political support (and pressure) and oftentimes funding to do so, as to create more healthy and resilient forests that will help mitigate against future fires and drought-driven tree mortality events. Yet many challenges remain in doing so at the scale that is needed, including proximity to, and lack of operational mills, a complex political climate, very limited time windows to safely burn, etc. Additionally, substantial science is ongoing in these forests to better understand exactly what happened, the resulting forest change, and what may happen in/to our future forests.