2 literature references:

Author: Liu, T.S.
Year: 1971
Title: A monograph of the genus Abies
Source: Dept. of Forestry, National Taiwan University, Taipei
Author: Krüssmann, G.
Year: 1983
Title: Handbuch der Nadelgehölze, 2. Auflage
Source: Paul Parey, Berlin & Hamburg