The topic is development of single-story housing into apartments. The Bay Area is rife with short houses around transit terminals.
You would have less traffic in the Valley if there were more apartments, so employees could bike and walk to work. They now commute from neighboring cities.
This assumes that all of the houses vacated by currently commuting employees moving into apartments near transit (and thus becoming non-commuters) would be replaced by people who don't commute. But that's extremely unlikely to be the case.
Furthermore, all of the people living near transit would still drive on occasion, so traffic would almost certainly get worse.
Other potential nudges would be to waive parking requirements for such development, thus denying parking places for the residents.
But redwood forests are a distraction. The main problem is SFH which can and would be replaced with duplexes and fourplexes if the market were allowed to work.
Much of the forest land on the peninsula is privately owned, not by individuals, but by conservation organizations.
> The main problem is SFH
Except that people like their yards and pools.
All else being equal, denser housing is better. But all else is rarely equal. Almost invariably, increased density comes with increased population. The SFH it replaces doesn't get turned back into open space, it remains SFH. Or it turns into more MFH, so now you have N times as many people living in the same space. That is the problem.
Immigration is not a problem. It is an opportunity.
N people live in a place. K people want to move there. You can either find ways to accommodate N+K people, or you can choose not to and have the richest people drive out the poorest (or the middle class if you start building affordable housing). Only one of those two options is classist and xenophobic. Take your pick.
I love hiking in redwood forests. I love peace and quiet. I love not having to deal with traffic. So I think undeveloped land is very useful.