Here is a good view of a stand that has almost fully transitioned from a black oak forest to a Douglas-fir stand. Encroachment began in this stand in the 1960s and finally the last of the taller oaks are reaching the end of their lives. Over then next ten or so years the oak stems will loose all of their limbs and begin to feel the pull of gravity as their root masses die. Many species of insects and fungus will invade these trees and speed up the fall. Once on the ground, the boles will persist for decades as the forest recyclers slowly and consistently do their work.
Meanwhile the Douglas-fir canopy will close in around the space previously occupied by the oaks and the little remaining areas of filtered light on the forest floor will become dark. This will also effect the shrub and ground cover component of the forest, severely limiting what can grow there in the absence of light.
Its interesting how the full encroachment cycle changes the bio-diversity of stand over time. It would seem that during the last phases of transition, like in the photo, the diversity is highest. This is in part due to the vertical structure offered by the overstory conifer, the decaying oak trees in the mid canopy, and the collection of downed wood on the forest floor. There are also pockets of shrubs that still receive light where the fir canopy has not closed in. Oak snags make potential cavities for numerous birds and mammals. The fallen trees become home to hosts of insects that in turn are feasted on by many of the locals.
While I generally speak of this encroachment as a negative, there is certainly a positive, or at least productive element to this process from a forest health prospective. In a truly “natural” setting, there would be recruitment of oak woodlands somewhere near-by while this process was occurring, creating the balance of habitats over the landscape. However in our fire starved environment, Douglas-fir encroachment is occurring much more frequently than the rate oak stands are developing. In fact, very little oak stands are developing at all in Humboldt County. This is why, I believe, that there is an urgency to prevent encroachment into woodlands.
Nooks and Crannies 
I would suggest a call to the forest activists among our local citizenry to rally behind this effort. Perhaps a few tree sits are due to create awareness. Oh, wait, there’s no timber company to sue for their efforts. Ask any Humboldt oldtimer and they’ll tell you the oak stands of the past in our back country are all but gone. Sadly, nature bats last and white oak is just not sexy enough. I must ask, are there any measures humans can take to slow this encroachment?
Perhaps my inner snarkiness came out there a bit. There are forest preservationists who do care about our natural environs and there are others in it for the sheer showmanship. I didn’t mean to demean those who do the good environmental work, but I will hold onto my words for those who don’t.
I get it. Although I would say its not activism we need to solve this problem, at least not in the woods. Dealing with fire is #1 and that is very complicated. Is it even possible to restore fire to the landscape at large?
As of now, people who have this problem need to get their asses out there with chainsaws and remove the fir from under the oaks when they are still young. Many of the people I work with are hiring hand crews to go in and cut out the fir in 20-40 acre blocks at a time. Its allot of work though, and not really ideal. Hopefully in the next 10 years we will have a better mechanism for controlled fire.
Fire as a tool is difficult. Even if you have an area appropriate for burning, unless your acreage is huge, and the fire can be contained easily, the liability is too great (unless you’re Red Emmerson/AB1492). So it’s chainsaw work. I’ve slaughtered 1000’s of young Douglas Fir seedlings under the Oaks (Oregon White and Canyon Live Oak. Taller Firs I girdle, habitat or firewood after they die and dry out. This of course contrary to conventional forestry, which favors a monoculture Conifer plantation. But, the CDF is starting to accommodate this approach, and NRCS really is on board (monies available).
If you need a recommendation for a hand crew, I’d give John-Luis at the Bridgeville fire-safe group a thumbs up.