Converts farnesyl diphosphate to alpha-bisabolene (PubMed:9618485, PubMed:9539701, PubMed:22153510). Involved in defensive oleoresin formation in conifers in response to insect attack or other injury (PubMed:9618485, PubMed:9539701). Involved in sesquiterpene (C15) olefins biosynthesis (PubMed:9618485, PubMed:9539701). (2E,6E)-farnesyl diphosphate = (E,R)-alpha-bisabolene + diphosphate Binds 3 divalent metal cations per subunit (PubMed:22153510). Can use either Mg(2+) or Mn(2+) (PubMed:9618485). Terpene metabolism; oleoresin biosynthesis. By wounding. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). The conserved 25-Arg-Arg-26 motif may play a role in the isomerization step of the terpenoid cyclization reaction sequence. Belongs to the terpene synthase family. Tpsd subfamily.