According to this article (Guitar Player Jan. 1976):

For tunings on the electrics and acoustics he uses standard, open E, open D, and a "Bruce Palmer Modal tuning," with the strings E, E,E, E, B, and E, working from the bass strings first. This tuning was used for his interludes on "Suite: Judy Blue Eyes" (Crosby, Stills, and Nash, Atlantic, At S-8229).