I would read "under the redwood" to include anything in the soil under tree. Redwood have extensive root systems and most tree's root systems exist in symbiosis

I would read "under the redwood" to include anything in the soil under tree. Redwood have extensive root systems and most tree's root systems exist in symbiosis with bacteria. In addition all the dead plant matter (even coniferous -> acidic) is a massive food source for fungi and insects. "Forest floors are notoriously sterile places" - Not sure where you'd get that idea. In my neck of the woods (pun intended) most forest floors are so covered with ferns and brush you can't go off trail without serious bushwhacking. Older growth, which tend to be more open on the floor, are nevertheless loaded with shade loving plants, fungi, insects, small mammals...