" There is also a very large, and interesting plantation of them in Maui, not the southeast, but still a really warm humid climate" Nope! Wrong again! The redwoods there are mostly planted above 5000', a climate where dewpoints are always << 60F, thus nights are going to be in the 50s at worse, and even 30s and 40s in winter. Highs probably never hit 80f, even during the worst heatwaves. Not at all a "really warm humid climate". A few are a bit lower, down to 3000', but their growth seems to become abnormal. Even there, summer are as cool or cooler than Boston's!

The tree is small, at under 1 foot fall and 1 foot wide. Up until a month ago, I had it in a half gallon container and under 16 hours per day of artificial light. I transfered it into a 5 gallon pot and under sunlight after I noticed the symptoms described in my original post. When I transplanted, the roots looked OK. The leafs in the picture grew 12 months ago. All leafs on the plant are like this. I see dormant stem buds, but no above soil growth. There may be root growth under the soil. When watering, the topsoil eroded a bit and I noticed a few new, thin and white surface level roots. Should I wait for growth in the spring to see if new growth is infected, before spraying with a fungicide?

Low forking of coast redwoods is frequent this far north. Whether there is a connection or not, coldest winters (example: 1990) here burn them. Although coast redwood, Oregon myrtle and tanoak make large specimens in cultivation here, and the first two even reseed, all three may get singed when temperatures bottom out - showing one of the reasons their northmost wild populations are all well south of our area. An interesting thing about the northernmost wild redwood grove, on the Chetco River is that dense growths of western hemlock seedlings are preventing it from reproducing. A forest ecologist friend seems to think it may be the hemlock rather than the cold that keeps it from occurring farther north, on its own. I'm not sure I buy it.

"Is Coast Redwood hardiness in the east limited by its root system...?" I would say it definitely isn't. The tops of mine have been burned in the past 2 winters, but the roots had no trouble pushing them to a quick recovery in the mid-spring. And that is without heavy mulch, too. The thought some "hardiness life force" will come up from the roots is mistaken. If anything, dawn redwood roots are "used" to getting to shut down in the winter. If that happened on a coast redwood top growth, it would be disastrous. One reason they can grow along the eastern seaboard, within reason, is very dry soil in winter here is statistically highly unlikely, compared with, say, parts of the midwest. cf: http://www.climatesource.com/images/ppt_jan.gif