Black Dragon Cryptomeria

I am having some trouble with my black dragon evergreens and wonder if anyone else has had the same problem? They brown out in areas many times at the bottom of the plant. They are planted with various exposures from part sun to full sun. We live in the mountains of Western North Carolina.

I only have one - here in the piedmont of NC - and no problems like that.
The black dragon is only around 5 feet tall. It isn't surrounded by other shrubs so it gets enough ventilation. I don't water - (it has been in ground about 3 years) and it has to survive on what nature provides. As you know we had a drought pretty significant last year and I maybe watered three times. So I don't think it needs a lot of water once established. It is facing west but there is a lot of tree shade.

My only problem w/ Black Dragon are the occasional revertants which need to be pruned out.
It does surprisingly well, since it is supposedly only marginally hardy here.

WeeR
What should I be looking for with revertants??
Are you describing what sometimes happens with japanese maple trees?

Thank you so much for your responses. Since they are only about 3' tall maybe lack of water until they are larger is the problem or maybe I have a little critter that I am not aware of. And I too would like to know what you mean by revertants?

A landscaper told me that if you suddenly have a branch or a part of an evergreen go brown... it is water issues. Either lack or too much (I know this seems unhelpful and ambiguous) but all I really had to do after that is figure out which it was.... I know how much I water or how much rain we've had and I know when we've had drought conditions and I haven't watered like I should.. ....so there is really no guessing. But I did understand him to say that this isn't a general uniform browning but when suddenly a part (limb/branch) goes brown.

Black dragon is a very compact cultivar of cryptomeria.
I have 2 Black dragon cryptomerias.
Each have occasionally developed exuberant growth of a revertant branch manifest by less congested foliage.
It clearly stands out from the typical foliage of Black Dragon.
It's easily managed by selective pruning.
Unfortunately, I never bothered to take a photo of typical revertant foliage.
It's quite distinct from the congested Black Dragon foliage.

Thank you all for your help. Sounds like a watering problem to me. With all the mature trees we have these little guys are probably being cheated out of their share of water. Thanks again.