What's going on with roots

A few weeks ago I started noticing a phenomenon near the ground level of the trunks. Thin dark hair-like structures were forming extending from the trunk. They looked very much like dead strings, being thin and seemingly dry. Eventually I began to realize that that was not the case - they are very much alive and a part of the growing sequoias.

Here is a close up on the #4, where these hairlike roots clearly started forming a web, which is now extending almost all the way into the soil:

#4 July 28, 2013

And here is even more magnification:

it appears, these are the new roots. They are extremely fragile, but I think in a few weeks they will form into full blown support structures.

All samples in 6" containers are doing fine. Several sequoias became extremely bushy. I decided to do an experiment with one of them by removing lower branches, leaving just a few top branches:

#63 July 28, 2013. Lower branches removed.

#202 is the youngest sample, which grows very well, outgrowing the majority of older samples:

#202 July 28, 2013