"Brierier" is not a correct spelling of the word "brier," which means a prickly bush. The correct spelling is "brier." The phonetic transcription of "brier" is /ˈbraɪər/. The "b" is pronounced like "br," the "ie" is pronounced like "ai," and the "r" is rolled. Adding an extra "i" and "e" to the word does not change its pronunciation, and therefore, it is unnecessary and incorrect. Always double-check your spellings to avoid errors like this.