If anyone is wondering why there are brown/yellow evergreen trees: bark beetles.
I wrote a research paper on this a while ago.
More than [102 million
have died in California since 2010 due to a combination of drought and disease. Normally, disease will only kill sick and old trees. However, unprecedented, extended low levels of winter precipitation throughout all of California has weakened tens of millions of trees. Trees have drought resilience, but can only last so many years. A compromised tree cannot properly defend itself from disease.
The most destructive disease has been [bark beetles](https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5384837.pdf
) (Mountain pine, Jeffrey Pine, Western Pine), which are insects smaller than a dime that bore into the cambia of trees. Bark beetles have ravaged Western US forests in the past two decades. Scientist attribute the bark beetle epidemic to hotter and drier climate, some
whom say it’s a consequence of anthropogenic climate change. The drought and bark beetles have taken the biggest toll in the Central and Southern Sierras. Pine trees (e.g. Grey, Knobcone, Ponderosa, Jeffrey, Lodgepole) have been impacted the greatest.
It’s important to note that of the 102 million dead trees, 62 million died in 2016, marking a 100% increase in mortality from 2015. Additionally, report was published November of 2016; likely many more trees have died since than.
Here’s a tree mortality [map](http://egis.fire.ca.gov/TreeMortalityViewer/
Here’s more information on the