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Nature does this on its own, given enough time.  Different tree species have evolved different strategies.  Some require a lot of sun, grow fast, and make a lot of seeds before being overshadowed by taller trees.  Others have evolved to tolerate shade, usually in return for being less competitive when there is a lot of light.

Here in the northeast US, the eastern hemlock (<i>Tsuga canadensis</i>) is one such tree.  It is very shade-tolerant, and large trees produce a lot of shade.  About the only tree that can grow underneath a bunch of hemlocks is another hemlock.  In fact, hemlocks require shade.  Like most trees, they do grow faster with more light, but don't utilize high light as well as fast-growing trees like birches.

As a result, hemlocks take a while to establish because they require a good canopy to compete.  Once they take hold, they form exclusive stands with no other seedlings being able to grow.  There are several hemlock groves in my town in north-central MA.  These are still young enough around here that there are tall white pines (<i>Pinus strobus</i>) interspersed with the hemlocks.  These pines are long-living, and left over from when the forest floor had more light.  New pines aren't growing, but the old ones may still be around for many decades.  They are taller than hemlock, so the hemlock don't shade the pines.

You aren't going to get "near total darkness", but hemlock groves do feel considerably darker than other forest types around here.