I know all about understory. I own 30 acres in Wisc. that was select cut
about 8-10 years ago and is pretty overgrown, not too bad but its
noticable.
Theres a 70 acre parcel next to me that has never been logged and has
virtually no understory to speak of. Another 40 acre parcel by me was
clear
cut and is overgrown with scrub making it virtually unpenetratable. The
deer
love it though.

Interesting! I'm not sure if this is true for you guys up there, but
back in New England, forests grow up almost spontaneously. If you
leave a field unmowed and uncultivated, it will spring back to an early
successional forest within a few years, and be pretty thick after about
15 or 20. Larger trees like the big hardwoods (rock maple, oaks,
cherries, beech, elms, nut trees) take longer, as do the yellow
pines...but the alders, willows, pussy willows and dry species go
bananas fast. Poplar species do well too. In 50 years, though, the
richness has returned, if not the absolute size of the trees.

The reason, in large part, is that New England gets plenty of rain
during the summer growth season. No such luck here in CA; although
some species grow really fast, getting them established is a very
hands-on proposition.

Bruce Jensen