My Cypress tree is balding.
How can I promot new brach growth?
If you are in the San Bruno area, there are many types of cypress trees, each one of these have their own set of pests and diseases and possible reasons for decline. The most common are Monterey cypress and Italian cypress. Both are susceptible to fungal canker disease, insect pests and drought stress.
Without photos and more information on the growing conditions, soil and water management, it's impossible to diagnosis remotely.
I suggest that you contact the UC Cooperative Extension office in Half Moon Bay, and specifically Dr Igor Lacan, a highly competant urban forestry specialist. They may provide free inspection and recommendations. http://cesanmateo.ucanr.edu/About/Contact/Half_Moon_Bay_Office_Staff/
Also, Bartlett Tree Service out of SF and Davey Tree in Brisbane.