There are a couple of factors that can contribute to these browning symptoms. To some extent, browning of the foliage is part of the normal growth pattern for Cryptomeria. Like many conifers, they will shed older foliage as they mature. The innermost foliage will be older overall and tends to brown and be retained for a time before shedding, as Cryptomeria foliage doesn't fall off as readily as, say, pine needles. As a species that prefers full sun, plants that receive some shade may shed proportionately more foliage (or do so at an earlier age) than those receiving more light. When you have several Cryptomerias planted this closely like this, as they mature, they will be in competition for sunlight, the larger ones casting shade on portions of the other(s).

There could be other issues at work too. For example, Cryptomeria Scale is a small insect, a type of armored scale, that feeds on the leaf cell contents. This can lead to yellowing, browning, and eventual dieback. These scales are very tiny and difficult to detect (you might need a hand lens to see them). If you want to send us photos of a branch that is starting to show symptoms, we might be able to see if scales are present. 

The pattern of browning on the tree on the left (third) photo suggests there might be a root decline problem as well. 

You can prune out the brown portions of the tree -- those areas will not come back. We would also recommend inspection of the trees by a certified arborist, to check for scale and or evidence of boring insect activity in the trunk. You can find a certified arborist near you using this directory from the International Society of Arboriculture, https://www.treesaregood.org/.

Christa

Joan, yes, the new growth you have there is a great sign! Thank you for sending these additional photos. I failed to be more specific in my first reply: scale insects, if present, would be most visible on the foliage portion, and a good place to look would be at a transition point between brown areas and green -- where you might observe yellowing or spotting of the foliage. We would need to see a closer image of an area like that, rather than the bark of the tree. Maskell scale is the type of scale that can cause troubles for Cryptomeria, if there is a heavy infestation. The photos on this page give examples of the tiny things we are looking for. https://content.ces.ncsu.edu/maskell-scale
If you are willing to send additional, closer photos, we'll take another look.

Christa

We took a close look at your photos with our plant pathologist this morning. We do not see a scale infestation and think the browning areas are more likely due to the crowding, competition, and shading, as noted in our original reply. We do not recommend any treatment for scale at this time.

Christa