Converts farnesyl diphosphate to alpha-bisabolene (PubMed:28096378). Involved in defensive oleoresin formation in conifers in response to insect attack or other injury (By similarity). Involved in sesquiterpene (C15) olefins biosynthesis (By similarity). (2E,6E)-farnesyl diphosphate = (E,R)-alpha-bisabolene + diphosphate Binds 3 divalent metal cations per subunit. Can use either Mg(2+) or Mn(2+). Terpene metabolism; oleoresin biosynthesis. Expressed in young and mature roots. Belongs to the terpene synthase family. Tpsd subfamily.