How long before the biomass buildup and the catastrophic wildfire?
It depends upon the distribution of proximate seed. My estimates for that successional process in our area (about 15-20 miles from there) are here. Our place can go from bare sand to closed canopy forest in 30 years.
I did have MidPen's cheese biologist (Cindy Roessler, now retired) visit the Wildergarten, twice. When she saw what I had done to bring back an aboriginal patch of blue dicks (Dichelostemma capitatum), she fell to her knees in disbelief. Later in the walk, she asked me, "What do you do to keep Coyote Bush (Baccharis pilularis)under control?" She'd seen a few shrubs here and there, but there weren't many and they surely weren't taking over. I responded without hesitation, "I cull the females." Looking at her shoes she repeated, "...cull the females," knowing that the powers that be at MidPen would never allow such a sexist policy. (snort!) That's how backward that agency really is.
But they do keep the developers and the banks happy building Sustained Development.