Thanks for writing. The brown stalks you're seeing are the fern's reproductive organs --- and happily, they don't really have any effect on the plants.
Most of the time in your area, the main reason ferns go brown prematurely is hot, dry conditions --- so be sure to keep the soil moist and your ferns should stay green longer. If you don't mulch the soil around them, a topdressing of 1-2 inches of compost in early spring can help a lot.
---Justin, Senior Garden Editor, BHG.com