Embers from wildland fires can enter your house through many different routes, but exterior vegetation is not the only fuel providing those embers. Wildland fires can also be spread from structure to structure or from a structure to wildland vegetation. The most important place to begin preparing defensible space is with your home. Fortifying or retrofitting your home can be your best defense against ember intrusion.
The key to protecting your home and property from fire is to start from the house out. The Wildland Urban Interface Building Standard, also known as Chapter 7A, is a new addition to the California Building Code, and it affects how new homes are built in wildfire-prone areas.