As a matter of fact, the California Division of Forestry has required regular thinning. It's the Bozo tree-hugging faction of Santa Cruz that prevents it.
You must understand that here in California, we have a particular species of moonbat: the Tree Sitter.
These odd creatures have a habit of nesting themselves in trees that they consider "sacred", so as to keep them from being cut down.
Currently, on the UC Berkeley campus, there are several of these Tree Sitters living in oak trees that the university is going to remove for a new building. The Tree Sitters insist on calling these trees by their pagan name: "Mother Oak". "Save the old growth Mother Oaks", they cry.
Sadly, "Mother Oak" was planted by gardners in 1923. These trees will be replaced with over 300 new ones.
You really cannot argue with the Tree Sitter. It's like arguing with a stone.